APL-UW Website - Profile - Kristin Laidre

First abundance estimate for the east Greenland polar bear subpopulation

Laidre, K.L., T.A. Marques, B. Cohen, R.G. Hansen, E.V. Regehr, M.J. Zahn, J. Aars, J. Ware, H.L. Stern, and F. Ugarte, "First abundance estimate for the east Greenland polar bear subpopulation," Endang. Species Res., 59, doi:10.3354/esr01479, 2026.

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12 Mar 2026

Evaluating the demographic status of large mammals in dynamic habitats is challenging. The east Greenland (EG) polar bear (Ursus maritimus) subpopulation ranges over approximately 1.5 million km² of sea ice and 18° of latitude along a mostly uninhabited coastline, making it the most expansive of the world's 20 polar bear subpopulations. We report on a distance-sampling aerial survey that provided the first estimate of abundance for EG polar bears. We used a density surface model (DSM) that corrected for incomplete detection on the transect line using mark-recapture methods, accounted for overall detectability via distance-sampling methods, and modeled bear density as a function of environmental covariates with a generalized additive model. Our study design was informed by Indigenous Knowledge surveys and 3 decades of polar bear movement data obtained from satellite telemetry. During March–May 2023, we flew 106.5 h on-effort over 26 survey days and sighted 84 groups of bears (108 individuals). Mean observed litter size was 1.6 (95% CI = 1.2–2.0) for cubs-of-the-year and 1.6 (95% CI = 1.3–1.8) for yearlings. Polar bear density was higher closer to land and along the continental shelf break offshore, where bathymetry deepens from 300 to 1000 m. Polar bear density was approximately 5 times lower within 50 km of subsistence hunting communities (0.06 bears 100 km^-2) compared to the rest to the study area (0.31 bears 100 km^-2). The best estimate of abundance for the EG subpopulation, adjusted for animals located outside the sampling area, was 2275 bears (CV = 0.27, 95% CI = 1360–3807). This estimate can be used to identify a sustainable level of subsistence harvest, manage human–bear conflicts, and monitor the effects of climate warming on EG polar bears. Our methods also provide a template for designing and conducting aerial surveys for wildlife populations inhabiting vast and remote regions.

Vulnerability of marine megafauna to global at-sea anthropogenic threats

VanCompernolle, M., and many others, including K. Laidre, "Vulnerability of marine megafauna to global at-sea anthropogenic threats," Conserv. Biol., 40, doi:10.1111/cobi.70147, 2026.

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1 Feb 2026

Marine megafauna species are affected by a wide range of anthropogenic threats. To evaluate the risk of such threats, species' vulnerability to each threat must first be determined. We build on the existing threats classification scheme and ranking system of the International Union for Conservation of Nature (IUCN) Red List of Threatened Species by assessing the vulnerability of 256 marine megafauna species to 23 at-sea threats. The threats we considered included individual fishing gear types, climate-change-related subthreats not previously assessed, and threats associated with coastal impacts and maritime disturbances. Our ratings resulted in 70 species having high vulnerability (v > 0.778 out of 1) to at least 1 threat, primarily drifting longlines, temperature extremes, or fixed gear. These 3 threats were also considered to have the most severe effects (i.e., steepest population declines). Overall, temperature extremes and plastics and other solid waste were rated as affecting the largest proportion of populations. Penguins, pinnipeds, and polar bears had the highest vulnerability to temperature extremes. Bony fishes had the highest vulnerability to drifting longlines and plastics and other solid waste; pelagic cetaceans to 4 maritime disturbance threats; elasmobranchs to 5 fishing threats; and flying birds to drifting longlines and 2 maritime disturbance threats. Sirenians and turtles had the highest vulnerability to at least one threat from all 4 categories. Despite not necessarily having severe effects for most taxonomic groups, temperature extremes were rated among the top threats for all taxa except bony fishes. The vulnerability scores we provide are an important first step in estimating the risk of threats to marine megafauna. Importantly, they help differentiate scope from severity, which is key to identifying threats that should be prioritized for mitigation.

Ringed seal (Pusa hispida) haul-out behavior and emergence timing in the Bering, Chukchi, and Beaurfort seas

Lindsay, J.M., P.B. Conn, P.L. Boveng, J.A. Crawford, L.T. Quakenbush, A.L. Von Duyke, and K.L. Laidre, "Ringed seal (Pusa hispida) haul-out behavior and emergence timing in the Bering, Chukchi, and Beaurfort seas," Ecol. Evol., 16, doi:10.1002/ece3.72948, 2026.

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25 Jan 2026

Ringed seals are ice-associated marine mammals that excavate lairs in snowdrifts on sea ice during winter for resting and pupping. Before lairs melt in the spring, seals shift from predominantly hauling out in lairs to predominantly hauling out on the surface of the ice to bask and molt, a transition we refer to as "emergence." Emergence timing is poorly understood, which hinders planning and interpretation of aerial surveys for population monitoring. We used hidden Markov models (HMMs) to analyze haul-out timelines from satellite-linked transmitters to estimate emergence dates of ringed seals from 2005 to 2021 in the Bering, Chukchi, and Beaufort seas. Our HMMs were fit separately for adults and subadults and included a lair state and an emerged state, characterized by differences in diel behavior and the daily proportion of time seals spent hauled out. We explored covariates of the transition probability between states, including day of year, daylength, sea-ice concentration, air temperature, and indices of snow melt progression. Emergence probability for adults was associated with longer daylengths and warmer temperatures. Median emergence date was 12 May (within 3 days of previous estimates from aerial surveys) and emergence date was positively associated with latitude. Subadults showed weaker seasonal changes in haul-out behavior, potentially making HMMs more suitable for adults than subadults. Our results contribute to our understanding of ringed seal behavioral ecology, provide useful information for aerial surveys, and demonstrate the value of haul-out data from tagged ringed seals for monitoring emergence timing in a warming Arctic.

Hair growth rate estimation in North American ursids

Stern, J.H., and 12 others including K.L. Laidre, "Hair growth rate estimation in North American ursids," Conserv. Physiol., 13, doi:10.1093/conphys/coaf075, 2025.

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1 Dec 2025

The feeding ecology of wildlife populations has important implications for individual health, population productivity and distribution patterns. For ursids (bears), food resources and feeding behaviour primarily affect population dynamics via effects on cub production and survival. Much of what is known about the feeding ecology of bears is based on analyses of tissues collected from capture-based research efforts, harvested animals or non-invasive approaches. However, inference about diet from hair has been limited by a lack of quantitative data on the timing of the moult and hair growth rates. We conducted a study to develop and test two methods of quantifying hair growth rates of three species in the family Ursidae (n = 1 polar bear, Ursus maritimus; n = 3 black bears, Ursus americanus; n = 3 grizzly bears, Ursus arctos horribilis). We implemented visual and biochemical approaches, proven safe for humans and other mammals, in a zoo setting. These methods relied on voluntary bear behaviours trained using positive reinforcement. The two methods were: (i) applying a small patch of hair dye (or bleach) on the rump or foreleg, and (ii) feeding an isotopically labelled amino acid (glycine) capsule that 'marks' time at a particular location as it is incorporated within the hair. We collected hair at regular intervals (every 1–2 weeks) for five months from body locations on the bear consistent with commonly sampled collection points in wild-caught bears. We found that both methods effectively identified periods of hair growth and detected individual and seasonal variation in hair growth rates. Average guard hair growth rates ranged between 0.10 and 1.05 mm day^-1 across the three species. This study provides the first step for developing a foundation for incorporating seasonality in wild-collected bear hair samples by assessing growth over an annual cycle.

This paper evaluates two methods for quantifying the rate and timing of hair growth in bears and provides hair growth rate estimates for three species. We developed a method to measure seasonal hair growth rates and can accurately incorporate seasonality in the interpretation of ecological data from wild-collected bear hair samples.

Migratory Arctic char (Salvelinus alpinus) as a prey pulse for Arctic marine predators

Gilbert, M.J.H., L.N. Harris, A.L. Vail, K.L. Laidre, M.L. Mallory, and D.J. Yurkowski, "Migratory Arctic char (Salvelinus alpinus) as a prey pulse for Arctic marine predators," Ecology, 106, doi:10.1002/ecy.70177, 2025.

10 Aug 2025

Hemoglobin A1c is a retrospective indicator of denning in polar bears (Ursus maritimus)

Teman, S.J., T.C. Atwood, K.L. Laidre, E.E. Virgin, K.D. Rode, L.A. Rispoli, and E. Curry, "Hemoglobin A1c is a retrospective indicator of denning in polar bears (Ursus maritimus)," J. Mammal., EOR, doi:10.1093/jmammal/gyaf033, 2025.

27 Jun 2025

Measuring polar bear health using allostatic load

Teman, S.J., T.C. Atwood, S.J. Converse, T.L. Fry, and K.L. Laidre, "Measuring polar bear health using allostatic load," Conserv. Physiol., 13, doi:10.1093/conphys/coaf013, 2025.

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5 Mar 2025

The southern Beaufort Sea polar bear sub-population (Ursus maritimus) has been adversely affected by climate change and loss of sea ice habitat. Even though the sub-population is likely decreasing, it remains difficult to link individual polar bear health and physiological change to sub-population effects. We developed an index of allostatic load, which represents potential physiological dysregulation. The allostatic load index included blood- and hair-based analytes measured in physically captured southern Beaufort bears in spring. We examined allostatic load in relation to bear body condition, age, terrestrial habitat use and, over time, for bear demographic groups. Overall, allostatic load had no relationship with body condition. However, allostatic load was higher in adult females without cubs that used terrestrial habitats the prior year, indicating potential physiological dysregulation with land use. Allostatic load declined with age in adult females without cubs. Sub-adult males demonstrated decreased allostatic load over time. Our study is one of the first attempts to develop a health scoring system for free-ranging polar bears, and our findings highlight the complexity of using allostatic load as an index of health in a wild species. Establishing links between individual bear health and population dynamics is important for advancing conservation efforts.

Characterizing southeast Greenland fjord surface ice and freshwater flux to support biological applications

Moon, T.A., B. Cohen, T.E. Black, K.L. Laidre, H.L. Stern, and I. Joughin, "Characterizing southeast Greenland fjord surface ice and freshwater flux to support biological applications," Cryosphere, 18, 4845-4872, doi:10.5194/tc-18-4845-2024, 2024.

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29 Oct 2024

Southeast Greenland (SEG) is characterized by complex morphology and environmental processes that create dynamic habitats for top marine predators. Active glaciers producing solid-ice discharge, freshwater flux, offshore sea ice transport, and seasonal landfast-ice formation all contribute to a variable, transient environment within SEG fjord systems. Here, we investigate a selection of physical processes in SEG to provide a regional characterization that reveals physical system processes and supports biological research. SEG fjords exhibit high fjord-to-fjord variability regarding bathymetry, size, shape, and glacial setting, influencing some processes more than others. For example, during fall, the timing of offshore sea ice formation near SEG fjords progresses temporally when moving southward across latitudes, while the timing of offshore sea ice disappearance is less dependent on latitude. The rates of annual freshwater flux into fjords, however, are highly variable across SEG, with annual average input values ranging from ~1 x 10⁸ to ~1.25 x 10¹⁰ m³ (~0.1–12.5 Gt) for individual fjords. Similarly, the rates of solid-ice discharge in SEG fjords vary widely — partly due to the irregular distribution of active glaciers across the study area (60–70°N). Landfast sea ice, assessed for eight focus fjords, is seasonal and has a spatial distribution highly dependent on individual fjord topography. Conversely, glacial ice is deposited into fjord systems year-round, with the spatial distribution of glacier-derived ice depending on the location of glacier termini. As climate change continues to affect SEG, the evolution of these metrics will vary individually in their response, and next steps should include moving from characterization to system projection. Due to the projected regional ice sheet persistence that will continue to feed glacial ice into fjords, it is possible that SEG could remain a long-term refugium for polar bears and other ice-dependent species on a centennial to millennial scale, demonstrating a need for continued research into the SEG physical environment.

Icing-related injuries in polar bears (Ursus maritimus) at high latitudes

Laidre, K.L., and S.N. Atkinson, "Icing-related injuries in polar bears (Ursus maritimus) at high latitudes," Ecology, EOR, doi:, 2024.

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22 Oct 2024

We report on icing-related lesions observed in wild polar bears during live-capture research in two high-latitude subpopulations, Kane Basin (KB) and East Greenland (EG), between 2012 and 2022. We observed ice buildup, hair loss (alopecia), and skin ulcerations primarily affecting the feet of adult bears as well as other parts of the body. The most severely affected individuals had blocks of ice up to 30â€‰cm in diameter adhered to the foot pads, deep, bleeding ulcerations of foot pads, and exhibited lameness. These injuries have not been observed during previous research in these areas or reported in the scientific literature. To further document this phenomenon, we conducted interviews with Indigenous polar bear subsistence hunters in West and East Greenland and Nunavut regarding the frequency and potential causes of icing-related injuries.

The acoustic presence and migration timing of subarctic baleen whales in the Bering Strait in relation to environmental factors

Escajeda, E.D., K.M. Stafford, R.A. Woodgate, and K.L. Laidre, "The acoustic presence and migration timing of subarctic baleen whales in the Bering Strait in relation to environmental factors," Polar Bio., EOR, doi:10.1007/s00300-024-03314-0, 2024.

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17 Oct 2024

Subarctic baleen whales, including humpback (Megaptera novaeangliae), fin (Balaenoptera physalus), and gray whales (Eschrichtius robustus), migrate through the Bering Strait every summer to feed in the Chukchi Sea. When and where the whales are found in the region likely reflects environmental conditions. Using recordings collected between 2009 and 2018 from a hydrophone similar to 35 km north of the strait, we identified whale calls during the open-water season (May–December), examined migration timing, and investigated potential drivers of whale presence. The acoustic presence of fin and humpback whales varied across the years, while gray whales were consistently detected each year. We compared detection rates for October and November since these months had recordings each year. We observed the highest proportion of recordings with humpback whale calls for October–November in 2009, 2017, and 2018 (66–80% of recordings); the highest proportion of recordings with fin whale calls in 2015, 2017, and 2018 (75–79% of recordings); and the highest proportion of recordings with gray whale calls in 2013 and 2015 (46 and 51% of recordings, respectively). Fin and humpback whales departed the Bering Strait similar to 3 and 2 days later per year over the study period (p < 0.04). Both fin and humpback whales delayed their southward migration in years with warmer water temperatures (Pearson r >= 0.73, p < 0.02). Generalized additive models of location, shape, and scale identified day of the year, water temperatures, and the lagged presence of a thermal front the previous month as drivers of acoustic presence for all three species during the open-water season.

Narwhal (Monodon monoceros) associations with Greenland summer meltwater release

Laidre, K.L. M.J. Zahn, M. Simon, M. Ladegaard, K.M. Stafford, E. Phillips, T. Moon, H.L. Stern, and B. Cohen, "Narwhal (Monodon monoceros) associations with Greenland summer meltwater release," Ecosphere, 15, doi:10.1002/ecs2.70024, 2024.

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14 Oct 2024

Climate change is rapidly transforming the coastal margins of Greenland. At the same time, there is increasing recognition that marine-terminating glaciers provide unique and critical habitats to ice-associated top predators. We investigated the connection between a top predator occupying glacial fjord systems in Northwest Greenland and the properties of Atlantic-origin water and marine-terminating glaciers through a multiyear interdisciplinary project. Using passive acoustic monitoring, we quantified the summer presence and autumn departure of narwhals (Monodon monoceros) at glacier fronts in Melville Bay and modeled what glacier fjord physical attributes are associated with narwhal occurrence. We found that narwhals are present at glacier fronts after Greenland Ice Sheet peak summer runoff and they remain there during the period when the water column is becoming colder and fresher. Narwhals occupied glacier fronts when ocean temperatures ranged from –0.6 to 0.8°C and salinities between 33.2 and 34.0â€‰psu at around 200â€‰m depth and they departed on their southbound migration between October and November. Narwhals' departure was approximately 4â€‰weeks later in 2019 than in 2018, after an extreme 2019 summer heatwave event that also delayed sea ice formation by 2â€‰months. Our study provides further support for the niche conservative narwhal's preference for cold ocean temperatures. These results may inform projections about how future changes will impact narwhal subpopulations, especially those occupying Greenland glacial fjords.

Consistent seasonal hydrography from moorings at northwest Greenland glacier fronts

Zahn, M.J., K.L. Laidre, M. Simon, K.M. Stafford, M. Wood, J.K. Willis, E.M. Phillips, and I. Fenty, "Consistent seasonal hydrography from moorings at northwest Greenland glacier fronts," J. Geophys. Res., 129, doi:10.1029/2024JC021046, 2024.

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1 Sep 2024

Greenland's marine-terminating glaciers connect the ice sheet to the ocean and provide a critical boundary where heat, freshwater, and nutrient exchanges take place. Buoyant freshwater runoff from inland ice sheet melt is discharged at the base of marine-terminating glaciers, forming vigorous upwelling plumes. It is understood that subglacial plumes modify waters near glacier fronts and increase submarine glacier melt by entraining warm ambient waters at depth. However, ocean observations along Greenland's coastal margins remain biased toward summer months which limits accurate estimation of ocean forcing on glacier retreat and acceleration. Here, we fill a key observational gap in northwest Greenland by describing seasonal hydrographic variation at glacier fronts in Melville Bay using in situ observations from moorings deployed year-round, CTDs, and profiling floats. We evaluated local and remote forcing using remote sensing and reanalysis data products alongside a high-resolution ocean model. Analysis of the year-round hydrographic data revealed consistent above-sill seasonality in temperature and salinity. The warmest, saltiest waters occurred in spring (April–May) and primed glaciers for enhanced submarine melt in summer when meltwater plumes entrain deep waters. Waters were coldest and freshest in early winter (November–December) after summer melt from sea ice, glacier ice, and icebergs provided cold freshwater along the shelf. Ocean variability was greatest in the summer and fall, coincident with increased freshwater runoff and large wind events before winter sea ice formation. Results increase our mechanistic understanding of Greenland ice-ocean interactions and enable improvements in ocean model parameterization.

Assessing the risk of climate maladaptation for Canadian polar bears

Rivkin, L.R., and 17 others including K.L. Laidre, "Assessing the risk of climate maladaptation for Canadian polar bears," Ecol. Lett., 27, doi:10.1111/ele.14486, 2024.

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1 Aug 2024

The Arctic is warming four times faster than the rest of the world, threatening the persistence of many Arctic species. It is uncertain if Arctic wildlife will have sufficient time to adapt to such rapidly warming environments. We used genetic forecasting to measure the risk of maladaptation to warming temperatures and sea ice loss in polar bears (Ursus maritimus) sampled across the Canadian Arctic. We found evidence for local adaptation to sea ice conditions and temperature. Forecasting of genome-environment mismatches for predicted climate scenarios suggested that polar bears in the Canadian high Arctic had the greatest risk of becoming maladapted to climate warming. While Canadian high Arctic bears may be the most likely to become maladapted, all polar bears face potentially negative outcomes to climate change. Given the importance of the sea ice habitat to polar bears, we expect that maladaptation to future warming is already widespread across Canada.

Nursing behavior of wild polar bears in the Canadian High Arctic

Stirling, I., L.E. Burns, E.V. Regehr, K.L. Laidre, and C. Spencer, "Nursing behavior of wild polar bears in the Canadian High Arctic," Can. J. Zool., 102, 663-672, doi:10.1139/cjz-2024-0001, 2024.

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19 Jul 2024

During 17 spring and summer field seasons between 1973 and 1999, we documented 220 bouts of nursing by dependent polar bear (Ursus maritimus Phipps, 1774) cubs at Radstock Bay, Nunavut, Canada. The overall mean duration of nursing bouts for cubs-of-the-year (COY) and yearlings (YRLG) litters was 7.1 min (standard deviation (SD) = 3.3, range = 1–23). Mean nursing bout durations of one- and two-cub litters of COY and YRLG in spring and summer seasons ranged from 6.09 to 7.78 min and from 5.00 to 9.18 min, respectively. The overall mean duration of inter-nursing intervals for COY and YRLG litters was 5.7 h (SD = 4.9, range = 0.0–35.0). The mean inter-nursing interval for one-cub litters was 6.4 h (SD = 4.6, range = 0.0–20.2) and for two-cub litters was 5.1 h (SD = 5.1, range = 0.0–35.0). We found no evidence for effects of season or cub age class on nursing behavior. We found weak evidence that two-cub litters nurse slightly longer than one-cub litters, potentially reflecting reduced nursing efficiency due to sibling rivalry. There was neither evidence for diel patterns in nursing behavior nor a detectable relationship between the cessation of nursing and the onset of hunting or sleeping by the adult female.

Development of an 8K SNP chip to assess adaptive diversity and hybridization in polar bears

Miller, J.M., and 11 others including K.L. Laidre, "Development of an 8K SNP chip to assess adaptive diversity and hybridization in polar bears," Conserv. Genet. Resour., 16, 237-249, doi:10.1007/s12686-024-01359-1, 2024.

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13 Jun 2024

The polar bear (Ursus maritimus) is a species particularly vulnerable to the effects of climate change. As the climate warms, polar bears will be forced to move to more suitable habitats which are likely to shrink, adapt to the new conditions, or decline in population size. However, the genomic diversity within and among all 19 subpopulations of polar bears, and therefore their adaptive potential, is currently unknown. In addition, warmer climates are likely to result in more frequent contact between polar bears and grizzly bears (U. arctos), with which they can hybridize. Here we describe the development, quality control, and application of the Ursus maritimus V2 SNP chip. This 8 K SNP chip contains loci explicitly selected to assess both RAD-derived and transcriptome-derived loci, as well as SNPs to detect hybridization between species. A total of 7,239 loci (90.3% of those printed) were successfully genotyped, with over 99% genotype concordance for individuals typed in duplicate on this chip, and between individuals typed here and on the Ursus maritimus V1 SNP chip. Using simulations, we demonstrate that the markers have high accuracy and efficiency to detect hybridization and backcrosses between polar bears and grizzly bears. However, empirical analysis of 371 polar bears, 440 grizzly bears, and 8 known hybrids found no novel instances of recent hybridization. The Ursus maritimus V2 SNP chip provides a powerful tool for monitoring the adaptive potential of this species along with assessing population structure, quantitative genomics, and hybridization in polar bears.

An examination of the Wrangel Island sea ice thickness dipole

Ross, S., G.W.K. Moore, and K.L. Laidre, "An examination of the Wrangel Island sea ice thickness dipole," J. Geophys. Res., 129, doi:10.1029/2023JC020425, 2024.

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1 Jun 2024

The Beaufort Sea High is a high-pressure system located in the Beaufort Sea that influences ocean circulation in the western Arctic known as the Beaufort Gyre. Wrangel Island, located in the western Chukchi Sea, typically experiences easterly sea ice motion due to the Beaufort Gyre. We find that under these climatological conditions, moving ice is blocked by the island and accumulates on its eastern side, while ice on its western side continues to drift leaving an area of open water and reduced ice thickness along the western side of the island. This results in an ice thickness dipole across the island. A reversal in the atmospheric circulation across the western Arctic results in a dipole with the opposing sign. We find the dipole is present throughout the year and is strongest in January when the difference in ice thickness between the eastern and western sides of the island is approximately 1 m. During the spring, it is associated with the transient opening of a polynya to the west of the island. The dipole is the result of opposing ice divergence and convergence across the western Arctic and may impact ocean circulation and ecosystems within the Chukchi Sea.

Space-use strategies drive diet composition of Baffin Bay polar bears

Stern, J.H., K.L. Laidre, E.W. Born, O. Wiig, and M.A. Mckinney, "Space-use strategies drive diet composition of Baffin Bay polar bears," Ecosphere, 15, doi:10.1002/ecs2.4826, 2024.

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25 Apr 2024

Polar bears (Ursus maritimus) depend on sea ice to hunt their ice-associated prey. However, climate-induced sea ice loss is leading to changes in space-use strategies of polar bears, with bears in some subpopulations spending more time on land or selecting alternative habitats. One such documented alternative habitat is glacier ice, which provides year-round access to prey, although the feeding habits of polar bears using glacier ice relative to those following the retreating ice and/or seasonally moving onshore are not known. Here, we use adipose tissue from polar bears (nâ€‰=â€‰104) from the Baffin Bay subpopulation live-captured in Northwest Greenland during the springs of 2009–2013 to investigate dietary patterns between space-use strategies inferred from satellite telemetry data, while considering demographic and interannual variation. Using quantitative fatty acid signature analysis (QFASA) to generate diet estimates, ringed seals (Pusa hispida) and bearded seals (Erignathus barbatus) were estimated as the primary and secondary prey of Baffin Bay polar bears for all sex/age classes and sampling years, apart from a single anomalous year (2009) with a relatively high proportion of beluga (Delphinapterus leucas) and narwhal (Monodon monoceros). While demographic and short-term temporal variation was minimal, fatty acid signatures and QFASA-generated diet estimates clearly differed between polar bears using coastal and offshore space-use strategies. "Offshore" adult females (n = 31), which make long-distance movements across the Baffin Bay pack ice, had high proportions of C22-chain length monosaturated fatty acids and diet estimates that included beluga, narwhal, harp (Pagophilus groenlandicus), and hooded seal (Cystophora cristata). "Coastal" adult females (n = 6), which remain resident at glacier fronts in Northwest Greenland year-round including during the sea ice-free season, consumed proportionally more ringed seals (+13%) and similar proportions of bearded seal, but essentially no beluga and narwhal or harp and hooded seal. Thus, space-use strategy is a driver of intrapopulation diet variability. As space-use strategies change with ongoing loss of sea ice habitat, our results suggest important ramifications for polar bear feeding patterns.

Accurate species classification of Arctic toothed whale echolocation clicks using one-third octave ratios

Zahn, M.J., M. Ladegaard, M. Simon, K.M. Stafford, T. Sakai, and K.L. Laidre, "Accurate species classification of Arctic toothed whale echolocation clicks using one-third octave ratios," J. Acoust. Soc. Am., 155, 2359-2370, doi:10.1121/10.0025460, 2024.

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1 Apr 2024

Passive acoustic monitoring has been an effective tool to study cetaceans in remote regions of the Arctic. Here, we advance methods to acoustically identify the only two Arctic toothed whales, the beluga (Delphinapterus leucas) and narwhal (Monodon monoceros), using echolocation clicks. Long-term acoustic recordings collected from moorings in Northwest Greenland were analyzed. Beluga and narwhal echolocation signals were distinguishable using spectrograms where beluga clicks had most energy >30â€‰kHz and narwhal clicks had a sharp lower frequency limit near 20â€‰kHz. Changes in one-third octave levels (TOL) between two pairs of one-third octave bands were compared from over one million click spectra. Narwhal clicks had a steep increase between the 16 and 25â€‰kHz TOL bands that was absent in beluga click spectra. Conversely, beluga clicks had a steep increase between the 25 and 40â€‰kHz TOL bands that was absent in narwhal click spectra. Random Forest classification models built using the 16 to 25â€‰kHz and 25 to 40â€‰kHz TOL ratios accurately predicted the species identity of 100% of acoustic events. Our findings support the use of echolocation TOL ratios in future automated click classifiers for acoustic monitoring of Arctic toothed whales and potentially for other odontocete species.

First recorded ice entrapment of a beluga whale (Delphinapterus leucas) in east Greenland

Laidre, K.L., J. Ware, M. Zahn, P. Hegelund, and J. Aars, "First recorded ice entrapment of a beluga whale (Delphinapterus leucas) in east Greenland," Polar Res., 43, doi:10.33265/polar.v43.9844, 2024.

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28 Feb 2024

Beluga whales are rare along the coast of east Greenland and the closest recognized stock occurs around Svalbard. Here we report on an ice entrapment of an adult beluga whale (Delphinapterus leucas) in north-east Greenland. The whale was observed entrapped in the fast ice on 21 April 2023 in Loch Fyne (73°54'N, 21°51'W) during a visual aerial survey for polar bears (Ursus maritimus). The whale was located >100 km from open water (i.e., pack ice) and appeared in poor body condition. A literature review back to the early 1900s failed to produce any other records of beluga whale ice entrapments in east Greenland.

Demographic response of a high-Arctic polar bear (Ursus martitimus) subpopulation to changes in sea ice and subsistence harvest

Laidre, K.L., T.W. Arnold, E.V. Regehr, S.N. Atkinson, E.W. Born, O. Wiig, N.J. Lunn, M. Dyck, H.L. Stern, S. Stapleton, B. Cohen, and D. Paetkau, "Demographic response of a high-Arctic polar bear (Ursus martitimus) subpopulation to changes in sea ice and subsistence harvest," Endanger. Species Res., 51, 73-81, doi:10.3354/esr01239, 2023.

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25 May 2023

Climate change is a long-term threat to polar bears. However, sea-ice loss is hypothesized to provide transient benefits in high latitudes, where thick multiyear ice historically limited biological productivity and seal abundance. We used joint live-recapture and dead-recovery mark-recapture models to analyze data for one of the most northerly polar bear subpopulations, Kane Basin. The data consisted of 277 initial live captures and genetic identifications (1992–1997 = 150, 2012–-2014 = 127), 89 recaptures or re-identifications (1992–1997 = 53, 2012–2014 = 36), and 24 harvest returns of research-marked bears during 1992–2014. We estimated mean annual abundance of 357 bears (95% CI: 221–493) for 2013–2014. This suggests a likely increase relative to our estimate of 224 (95% CI: 145–303) bears in the mid-1990s and relative to a previously published estimate of 164 (95% CI: 94–234) bears in the mid-1990s that used some of the same data. This is also supported by an apparent increase in the density of bears in eastern Kane Basin during 2012–2014. Estimates of total survival for females ≥3 yr old (mean ± SE: 0.95 ± 0.04) and their dependent offspring were similar to previous estimates from the 1990s, and estimates of unharvested survival for females ≥3 yr (0.96 ± 0.04) appear sufficient for positive population growth. Estimates of total survival were lower for males ≥3 yr (0.87 ± 0.06). We documented a reduction in mortality associated with subsistence harvest, likely attributable to implementation of a harvest quota by Greenland in 2006. Our findings, together with evidence for increased range sizes, improved body condition for all sex and age classes, and stable reproductive metrics, show that this small high-Arctic polar bear subpopulation remains productive and healthy. These benefits are likely temporary given predictions for continued climate change.

Light-level geolocation as a tool to monitor polar bear (Ursus maritimus) denning ecology: A case study

Merkel, B., J. Aars, K.L. Laidre, J.W. Fox, "Light-level geolocation as a tool to monitor polar bear (Ursus maritimus) denning ecology: A case study," Anim. Biotelem., 11, doi:10.1186/s40317-023-00323-4, 2023.

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21 Mar 2023

Monitoring polar bears is logistically challenging and expensive. Traditionally, reproductive history has been assessed using permanent marks from physically captured individuals, which requires assumptions about reproductive history based on their status at the time of capture. This is often supplemented with economically costly satellite telemetry (ST) collars restricted to adult females, which yield data on space use and reproductive history.

This study assesses the potential of adapting light-level geolocation (Global location sensing or GLS) tags, developed for birds and fish, to estimate life history metrics for polar bears. Traditionally, GLS uses light intensity and time of day to estimate approximate twice-daily locations. This information, combined with temperature data, can be used to assess approximate locations of maternity denning events, denning timing, general space use, and population connectivity.

Adult females (nâ€‰=â€‰54) were equipped, some several times, with a total of 103 GLS in Svalbard and Greenland from 2012 to 2021. Of these, 44 were also equipped with 80 ST collars during this period. This yielded GLS and ST data records for each individual up to 9.4 years (mean 4.0 years) and 5.1 years (1.5 years), respectively. Combined with capture information, the GLS and ST collars were used to score reproductive history (determined presence or absence of maternity denning events) for 72–54% of bear winters during this period, respectively. Using GLS yielded on average 4.3 years of unbroken reproductive history records (up to 8 years for some individuals) including denning phenology and age at first reproduction. Additionally, geographic locations could be estimated during spring and autumn (when twilight was present) with an average daily accuracy of 93 km (4–1042 km) and 58 km (5–550 km) when aggregating by season.

This study establishes GLS as a powerful, low-cost method for polar bear population monitoring that can provide data on reproductive history, including age at first reproduction, and maternity denning location and phenology in programs with ongoing recapture. GLS can also be used to monitor males and immatures that cannot wear ST collars.

Characteristics of ringed seal Pusa hispida ('natchiq') denning habitat in Kotzebue Sound, Alaska, during a year of limited sea ice and snow

Lindsay, J.M., and 14 others including K.L. Laidre, "Characteristics of ringed seal Pusa hispida ('natchiq') denning habitat in Kotzebue Sound, Alaska, during a year of limited sea ice and snow," Mar. Ecol. Prog. Ser., 705, doi:10.3354/meps14252, 2023.

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9 Feb 2023

Sea ice and snow are essential to Arctic ecosystems, playing key roles in the lives of Arctic marine mammals and the Indigenous Peoples who rely on them. Ringed seals Pusa hispida (â€˜natchiqâ€™ in Inupiaq) use snow-covered dens on sea ice for pupping, but quantitative information on denning habitat requirements is limited, and it is unknown how changes in snow depth and sea-ice extent will impact ringed seals. Here, an Indigenous Elder Advisory Council and a multidisciplinary group of scientists used knowledge co-production to quantify fine-scale ringed seal habitat selection patterns in Kotzebue Sound, Alaska (USA), during a year of unprecedentedly limited snow and sea-ice availability. Together, we conducted unoccupied aerial vehicle-based surveys during spring 2019 and related seal counts to survey date, bathymetry, and novel proxies for snow depth and surface roughness that we derived from Landsat 8 surface reflectance and validated with on-ice measurements. Generalized additive models showed that counts of seal groups (all age classes) and pups were associated with later survey dates, deeper water, and habitat with bright Landsat 8 pixel values and intermediate pixel variability, which in turn were correlated with deep snow and surface roughness. We observed shallow snow depths, early sea-ice breakup, and high seal densities consistent with the extreme lack of ice available in 2019. Indigenous Knowledge, intentionally woven with scientific data, provided novel and more nuanced understandings of snow and sea-ice conditions for seals. Our results may give a glimpse at future ringed seal habitat and selection in a warming Arctic.

Quantifying the effect of ship noise on the acoustic environment of the Bering Strait

Escajeda, E.D., K.M. Stafford, R.A. Woodgate, and K.L. Laidre, "Quantifying the effect of ship noise on the acoustic environment of the Bering Strait," Mar. Pollut. Bull., 187, doi:10.1016/j.marpolbul.2022.114557, 2023.

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1 Feb 2023

The narrow Bering Strait provides the only gateway between the Pacific Ocean and the Arctic, bringing migrating marine mammals in close proximity to ships transiting the strait. We characterized ship activity in the Bering Strait during the open-water season (July–November) for 2013–2015 and quantified the impact of ship noise on third-octave sound levels (TOLs) for bands used by baleen whales (25–1000 Hz). Peak ship activity occurred in July–â€“September with the greatest overlap in ship noise and whale vocalizations observed in October. Ships elevated sound levels by ~4 dB on average for all TOL bands combined, and 250-Hz TOLs exceeding 100 dB re 1 μPa were recorded from two large vessels over 11 km away from the hydrophones. Our results show that ship noise has the potential to impact baleen whales in the Bering Strait and serve as a baseline for measuring future changes in ship activity in the region.

Fecal DNA metabarcoding shows credible short-term prey detections and explains variation in the gut microbiome of two polar bear subpopulations

Franz, M., and 8 others including K.L. Laidre, "Fecal DNA metabarcoding shows credible short-term prey detections and explains variation in the gut microbiome of two polar bear subpopulations," Mar. Ecol. Prog. Ser., 704, 131-147, doi:10.3354/meps14228, 2023.

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26 Jan 2023

This study developed and evaluated DNA metabarcoding to identify the presence of pinniped and cetacean prey DNA in fecal samples of East Greenland (EG) and Southern Beaufort Sea (SB) polar bears Ursus maritimus sampled in the spring of 2015–2019. Prey DNA was detected in half (49/92) of all samples, and when detected, ringed seal Pusa hispida was the predominant prey species, identified in 100% (22/22) of EG and 81% (22/27) of SB polar bear samples with prey DNA detected. Bearded seal Erignathus barbatus DNA was found in 19% (5/27) of SB polar bear samples for which prey DNA was detected. Prey DNA detection frequencies and relative abundances were compared to estimates from quantitative fatty acid signature analysis (QFASA) for a subset of SB polar bears. Ringed seal and bearded seal were the main prey identified by both methods, but QFASA also identified 2 cetacean prey species not found by prey DNA. Differences in DNA metabarcoding vs. QFASA results were likely related to the different dietary timescales captured by each approach, i.e. short-term vs. long-term diet, respectively. Prey DNA detection, sex/age class, and subpopulation significantly explained variation in polar bear gut bacterial composition. Polar bear samples with prey DNA detected were associated with higher abundances of the bacterial classes Clostridia and Bacilli and lower abundances of Negativicutes. Fecal DNA metabarcoding is thus useful for identifying recent prey of polar bears, complementing quantitative and likely longer-term QFASA estimates, and may help understand variation in the polar bear gut microbiome.

An interdisciplinary perspective on Greenland's changing coastal margins

Straneo, F., and 12 others including K. Laidre, "An interdisciplinary perspective on Greenland's changing coastal margins," Oceanography, 35, 106-117, doi:10.5670/oceanog.2022.128, 2022.

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1 Dec 2022

Greenland's coastal margins are influenced by the confluence of Arctic and Atlantic waters, sea ice, icebergs, and meltwater from the ice sheet. Hundreds of spectacular glacial fjords cut through the coastline and support thriving marine ecosystems and, in some places, adjacent Greenlandic communities. Rising air and ocean temperatures, as well as glacier and sea-ice retreat, are impacting the conditions that support these systems. Projecting how these regions and their communities will evolve requires understanding both the large-scale climate variability and the regional-scale web of physical, biological, and social interactions. Here, we describe pan-Greenland physical, biological, and social settings and show how they are shaped by the ocean, the atmosphere, and the ice sheet. Next, we focus on two communities, Qaanaaq in Northwest Greenland, exposed to Arctic variability, and Ammassalik in Southeast Greenland, exposed to Atlantic variability. We show that while their climates today are similar to those of the warm 1930sÂ–1940s, temperatures are projected to soon exceed those of the last 100 years at both locations. Existing biological records, including fisheries, provide some insight on ecosystem variability, but they are too short to discern robust patterns. To determine how these systems will evolve in the future requires an improved understanding of the linkages and external factors shaping the ecosystem and community response. This interdisciplinary study exemplifies a first step in a systems approach to investigating the evolution of Greenland's coastal margins.

Marine mammal hotspots across the circumpolar Arctic

Hamilton, C.D., and 55 others including K.L. Laidre, "Marine mammal hotspots across the circumpolar Arctic," Divers. Distrib., 28, 2729-2753, doi:10.1111/ddi.13543, 2022.

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1 Dec 2022

A total of 2115 biologging devices were deployed on marine mammals from 13 species in the Arctic from 2005 to 2019. Getis-Ord Gi* hotspots were calculated based on the number of individuals in grid cells for each species and for phylogenetic groups (nine pinnipeds, three cetaceans, all species) and areas with high species richness were identified for summer (Jun-Nov), winter (Dec-May) and the entire year. Seasonal habitat differences among speciesâ€™ hotspots were investigated using Principal Component Analysis.

Hotspots and areas with high species richness occurred within the Arctic continental-shelf seas and within the marginal ice zone, particularly in the "Arctic gateways" of the north Atlantic and Pacific oceans. Summer hotspots were generally found further north than winter hotspots, but there were exceptions to this pattern, including bowhead whales in the Greenland-Barents Seas and species with coastal distributions in Svalbard, Norway and East Greenland. Areas with high species richness generally overlapped high-density hotspots. Large regional and seasonal differences in habitat features of hotspots were found among species but also within species from different regions. Gap analysis (discrepancy between hotspots and IUCN ranges) identified species and regions where more research is required.

This study identified important areas (and habitat types) for Arctic marine mammals using available biotelemetry data. The results herein serve as a benchmark to measure future distributional shifts. Expanded monitoring and telemetry studies are needed on Arctic species to understand the impacts of climate change and concomitant ecosystem changes (synergistic effects of multiple stressors). While efforts should be made to fill knowledge gaps, including regional gaps and more complete sex and age coverage, hotspots identified herein can inform management efforts to mitigate the impacts of human activities and ecological changes, including creation of protected areas.

Using visual observations to compare the behavior of previously immobilized and non-immobilized wild polar bears

Stirling, I., E.V. Regehr, C. Spencer, L.E. Burns, and K.L. Laidre, "Using visual observations to compare the behavior of previously immobilized and non-immobilized wild polar bears," Arctic, 75, 398-412, doi:10.14430/arctic76118, 2022.

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1 Dec 2022

During 17 field seasons between 1973 and 1999, we conducted a long-term study of the behavior of undisturbed wild polar bears in Radstock Bay, southwest Devon Island, Nunavut. In a subset of 11 seasons (6 spring and 5 summer) between 1975 and 1997, we used three different drug combinations to chemically immobilize a small number of adult and subadult polar bears on an opportunistic basis and applied a temporary dye mark so that individual bears could be visually reidentified. We then used multinomial logistic regression to compare the behavior of 35 previously immobilized bears of five different demographic classes (sex, age, and reproductive status) to the behavior of non-immobilized bears of the same demographic classes in the same years and seasons. During the first two days after immobilization, bears slept significantly more and spent less time hunting than did bears that had not been immobilized. However, previously immobilized bears returned to the same behavioral patterns and proportion of total time spent hunting as non-immobilized bears within two days and no further negative behavioral effects were detected in the following 21 d. We visually confirmed successful hunting by three adult bears within 0.4 to 2.1 d of being immobilized, all of which went on to make additional kills within the following 24 h. The return to normal behavior patterns, including the ability to hunt successfully, within 48 h of immobilization appears consistent with the hypothesis that polar bears do not experience longer-term behavioral effects following brief chemical immobilization for conservation and management purposes.

Thick and old sea ice in the Beaufort Sea during summer 2020/21 was associated with enhanced transport

Moore, G.W.K., M. Steele, A.J. Schweiger, J.L. Zhang, and K.L. Laidre, "Thick and old sea ice in the Beaufort Sea during summer 2020/21 was associated with enhanced transport," Commun. Earth Environ., 3, doi:10.1038/s43247-022-00530-6, 2022.

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30 Aug 2022

The Arctic Ocean has seen a remarkable reduction in sea ice coverage, thickness and age since the 1980s. These changes are most pronounced in the Beaufort Sea, with a transition around 2007 from a regime dominated by multi-year sea ice to one with large expanses of open water during the summer. Using satellite-based observations of sea ice, an atmospheric reanalysis and a coupled ice-ocean model, we show that during the summers of 2020 and 2021, the Beaufort Sea hosted anomalously large concentrations of thick and old ice. We show that ice advection contributed to these anomalies, with 2020 dominated by eastward transport from the Chukchi Sea, and 2021 dominated by transport from the Last Ice Area to the north of Canada and Greenland. Since 2007, cool season (fall, winter, and spring) ice volume transport into the Beaufort Sea accounts for ~45% of the variability in early summer ice volume — a threefold increase from that associated with conditions prior to 2007. This variability is likely to impact marine infrastructure and ecosystems.

Glacial ice supports a distinct and undocumented polar bear subpopulation persisting in late 21st-century sea-ice conditions

Laidre, K.L. and 18 others including E.V. Regehr, B. Cohen, and H.L. Stern, "Glacial ice supports a distinct and undocumented polar bear subpopulation persisting in late 21st-century sea-ice conditions," Science, 376, 1333-1338, doi:10.1126/science.abk2793, 2022.

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17 Jun 2022

Polar bears are susceptible to climate warming because of their dependence on sea ice, which is declining rapidly. We present the first evidence for a genetically distinct and functionally isolated group of polar bears in Southeast Greenland. These bears occupy sea-ice conditions resembling those projected for the High Arctic in the late 21st century, with an annual ice-free period that is >100 days longer than the estimated fasting threshold for the species. Whereas polar bears in most of the Arctic depend on annual sea ice to catch seals, Southeast Greenland bears have a year-round hunting platform in the form of freshwater glacial mÃ©lange. This suggests that marine-terminating glaciers, although of limited availability, may serve as previously unrecognized climate refugia. Conservation of Southeast Greenland polar bears, which meet criteria for recognition as the worldâ€™s 20th polar bear subpopulation, is necessary to preserve the genetic diversity and evolutionary potential of the species.

A polar bear paleogenome reveals extensive ancient gene flow from polar bears into brown bears

Wang, M.-S., and 14 others including K.L. Laidre, "A polar bear paleogenome reveals extensive ancient gene flow from polar bears into brown bears," Nat. Ecol. Evol., 6, 936-944, doi:10.1038/s41559-022-01753-8, 2022.

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16 Jun 2022

Polar bears (Ursus maritimus) and brown bears (Ursus arctos) are sister species possessing distinct physiological and behavioural adaptations that evolved over the last 500,000 years. However, comparative and population genomics analyses have revealed that several extant and extinct brown bear populations have relatively recent polar bear ancestry, probably as the result of geographically localized instances of gene flow from polar bears into brown bears. Here, we generate and analyse an approximate 20X paleogenome from an approximately 100,000-year-old polar bear that reveals a massive prehistoric admixture event, which is evident in the genomes of all living brown bears. This ancient admixture event was not visible from genomic data derived from living polar bears. Like more recent events, this massive admixture event mainly involved unidirectional gene flow from polar bears into brown bears and occurred as climate changes caused overlap in the ranges of the two species. These findings highlight the complex reticulate paths that evolution can take within a regime of radically shifting climate.

Passive acoustic monitoring reveals year-round marine mammal community composition off Tasiilaq, Southeast Greenland

Mattmueller, R.M., K. Thomisch, I. Van Opzeeland, K.L. Laidre, and M. Simon, "Passive acoustic monitoring reveals year-round marine mammal community composition off Tasiilaq, Southeast Greenland," J. Acoust. Soc. Am., 151, 1380-1392, doi:10.1121/10.0009429, 2022.

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28 Feb 2022

Climate-driven changes are affecting sea ice conditions off Tasiilaq, Southeast Greenland, with implications for marine mammal distributions. Knowledge about marine mammal presence, biodiversity, and community composition is key to effective conservation and management but is lacking, especially during winter months. Seasonal patterns of acoustic marine mammal presence were investigated relative to sea ice concentration at two recording sites between 2014 and 2018, with one (65.6°N, 37.4°Â°W) or three years (65.5°N, 38.0°W) of passive acoustic recordings. Seven marine mammal species were recorded. Bearded seals were acoustically dominant during winter and spring, whereas sperm, humpback, and fin whales dominated during the sea ice-free summer and autumn. Narwhals, bowhead, and killer whales were recorded only rarely. Song-fragments of humpback whales and acoustic presence of fin whales in winter suggest mating-associated behavior taking place in the area. Ambient noise levels in 1/3-octave level bands (20, 63, 125, 500, 1000, and 4000â€‰Hz), ranged between 75.6 to 105 dB re 1 μPa. This study provides multi-year insights into the coastal marine mammal community composition off Southeast Greenland and suggests that the Tasiilaq area provides suitable habitat for various marine mammal species year-round.

Distinct gut microbiomes in two polar bear subpopulations inhabiting different sea ice ecoregions

Franz, M., L. Whyte, T.C. Atwood, K.L. Laidre, D.Roy, S.E. Watson, E. Gongora, and M.A. McKinney, "Distinct gut microbiomes in two polar bear subpopulations inhabiting different sea ice ecoregions," Sci. Rep., 12, doi:10.1038/s41598-021-04340-2, 2022.

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11 Jan 2022

Gut microbiomes were analyzed by 16S rRNA gene metabarcoding for polar bears (Ursus maritimus) from the southern Beaufort Sea (SB), where sea ice loss has led to increased use of land-based food resources by bears, and from East Greenland (EG), where persistent sea ice has allowed hunting of ice-associated prey nearly year-round. SB polar bears showed a higher number of total (940 vs. 742) and unique (387 vs. 189) amplicon sequence variants and higher inter-individual variation compared to EG polar bears. Gut microbiome composition differed significantly between the two subpopulations and among sex/age classes, likely driven by diet variation and ontogenetic shifts in the gut microbiome. Dietary tracer analysis using fatty acid signatures for SB polar bears showed that diet explained more intrapopulation variation in gut microbiome composition and diversity than other tested variables, i.e., sex/age class, body condition, and capture year. Substantial differences in the SB gut microbiome relative to EG polar bears, and associations between SB gut microbiome and diet, suggest that the shifting foraging habits of SB polar bears tied to sea ice loss may be altering their gut microbiome, with potential consequences for nutrition and physiology.

Soundscape and ambient noise levels of the Arctic waters around Greenland

Ladegaard, M., and 8 others including K.L. Laidre, "Soundscape and ambient noise levels of the Arctic waters around Greenland," Sci. Rep., 11, doi:10.1038/s41598-021-02255-6, 2021.

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3 Dec 2021

A longer Arctic open water season is expected to increase underwater noise levels due to anthropogenic activities such as shipping, seismic surveys, sonar, and construction. Many Arctic marine mammal species depend on sound for communication, navigation, and foraging, therefore quantifying underwater noise levels is critical for documenting change and providing input to management and legislation. Here we present long-term underwater sound recordings from 26 deployments around Greenland from 2011 to 2020. Ambient noise was analysed in third octave and decade bands and further investigated using generic detectors searching for tonal and transient sounds. Ambient noise levels partly overlap with previous Arctic observations, however we report much lower noise levels than previously documented, specifically for Melville Bay and the Greenland Sea. Consistent seasonal noise patterns occur in Melville Bay, Baffin Bay and Greenland Sea, with noise levels peaking in late summer and autumn correlating with open water periods and seismic surveys. These three regions also had similar tonal detection patterns that peaked in May/June, likely due to bearded seal vocalisations. Biological activity was more readily identified using detectors rather than band levels. We encourage additional research to quantify proportional noise contributions from geophysical, biological, and anthropogenic sources in Arctic waters.

An on-ice aerial survey of the Kane Basin polar bear (Ursus maritimus) subpopulation

Wiig, Ø., S.N. Atkinson, E.W. Born, S. Stapleton, T. Arnold, M. Dyck, K.L. Laidre, N.J. Lunn, and E.V. Regehr, "An on-ice aerial survey of the Kane Basin polar bear (Ursus maritimus) subpopulation," Polar Biol., 45, 89-100, doi:10.1007/s00300-021-02974-6, 2021.

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22 Nov 2021

There is an imminent need to collect information on distribution and abundance of polar bears (Ursus maritimus) to understand how they are affected by the ongoing decrease in Arctic sea ice. The Kane Basin (KB) subpopulation is a group of high-latitude polar bears that ranges between High Arctic Canada and NW Greenland around and north of the North Water polynya (NOW). We conducted a line transect distance sampling aerial survey of KB polar bears during 28 April–12 May 2014. A total of 4160 linear kilometers were flown in a helicopter over fast ice in the fjords and over offshore pack ice between 76° 50' and 80° N'. Using a mark-recapture distance sampling protocol, the estimated abundance was 190 bears (95% lognormal CI: 87–411; CV 39%). This estimate is likely negatively biased to an unknown degree because the offshore sectors of the NOW with much open water were not surveyed because of logistical and safety reasons. Our study demonstrated that aerial surveys may be a feasible method for obtaining abundance estimates for small subpopulations of polar bears.

Acoustic differentiation and classification of wild belugas and narwhals using echolocation clicks

Zahn, M.J., S. Rankin, J.L.K. McCullough, J.C. Koblitz, F. Archer, M.H. Rasmussen, and K.L. Laidre, "Acoustic differentiation and classification of wild belugas and narwhals using echolocation clicks," Sci. Rep., 11, doi:10.1038/s41598-021-01441-w, 2021.

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12 Nov 2021

Belugas (Delphinapterus leucas) and narwhals (Monodon monoceros) are highly social Arctic toothed whales with large vocal repertoires and similar acoustic profiles. Passive Acoustic Monitoring (PAM) that uses multiple hydrophones over large spatiotemporal scales has been a primary method to study their populations, particularly in response to rapid climate change and increasing underwater noise. This study marks the first acoustic comparison between wild belugas and narwhals from the same location and reveals that they can be acoustically differentiated and classified solely by echolocation clicks. Acoustic recordings were made in the pack ice of Baffin Bay, West Greenland, during 2013. Multivariate analyses and Random Forests classification models were applied to eighty-one single-species acoustic events comprised of numerous echolocation clicks. Results demonstrate a significant difference between speciesâ€™ acoustic parameters where beluga echolocation was distinguished by higher frequency content, evidenced by higher peak frequencies, center frequencies, and frequency minimums and maximums. Spectral peaks, troughs, and center frequencies for beluga clicks were generallyâ€‰>â€‰60 kHz and narwhal clicksâ€‰<â€‰60 kHz with overlap between 40–60 kHz. Classification model predictive performance was strong with an overall correct classification rate of 97.5% for the best model. The most important predictors for species assignment were defined by peaks and notches in frequency spectra. Our results provide strong support for the use of echolocation in PAM efforts to differentiate belugas and narwhals acoustically.

Feeding habits of Baffin Bay polar bears Ursus maritimus: insight from stable isotopes and total mercury in hair

Stern, J.H., K.L. Laidre, E.W. Born, Ø. Wiig, C. Sonne, R. Dietz, A. Fisk, and M.A. McKinney, "Feeding habits of Baffin Bay polar bears Ursus maritimus: insight from stable isotopes and total mercury in hair," Mar. Ecol. Prog. Ser., 667, 233-244, doi:10.3354/meps13864, 2021.

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28 Oct 2021

Loss of sea ice brought on by climate change affects polar bear Ursus maritimus access to prey. Here we investigated variation in feeding habits of the Baffin Bay (BB) polar bear subpopulation in relation to sea ice, habitat use, season, and demography using hair carbon (δ¹³C), nitrogen δ¹⁵N), and sulfur (δ³⁴S) stable isotope values and total mercury (THg) concentrations as ecological tracers. We analyzed hair samples from BB polar bears (n = 131) of all age and sex classes live-captured in West Greenland during the spring in 2009–2013. BB polar bears occupied a narrow isotopic space, suggesting limited variation in carbon sources and trophic position within the subpopulation. THg concentrations (median +/– SE: 5.1 +/– 0.2, range: 0.3–12.5 μg g^-1 dry weight, DW were related to age class, and nearly half exceeded the suggested threshold for neurological effects in polar bears at 5.4 μg g^-1 DW. Although distinct coastal and offshore space-use strategies have been reported for BB polar bears, our results suggest that both strategies lead to similar carbon sources and trophic positions. We found seasonal variation in δ¹³C and δ³⁴S across both space-use strategies, with δ³⁴S suggesting that all BB polar bears may prey on a higher proportion of benthic-feeding bearded seals Erignathus barbatus in late summer relative to spring. Despite wide fluctuations in inter-annual sea ice conditions and differences in space-use strategies among individuals, stable isotope values and THg concentrations suggested limited variation in feeding habits among BB polar bears. The variation of habitat tracers (δ¹³C and δ³⁴S) was related to season, whereas trophic tracer (δ¹⁵N and THg) variation was driven by demographic group. The specialized BB polar bear diet suggests limited feeding plasticity under continued climate warming.

A novel mark-recapture-recovery survey using genetic sampling for polar bears Ursus maritimus in Baffin Bay

Atkinson, S.N., K.L. Laidre, T.W. Arnold, S. Stapleton, E.V. Regehr, E.W. Born, Ø. Wiig, M. Dyck, N.J. Lunn, H.L. Stern, and D. Paetkau, "A novel mark-recapture-recovery survey using genetic sampling for polar bears Ursus maritimus in Baffin Bay," Endanger. Species Res., 46, 105-120, doi:10.3354/esr01148, 2021.

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7 Oct 2021

Changes in sea-ice dynamics are affecting polar bears Ursus maritimus across their circumpolar range, which highlights the importance of periodic demographic assessments to inform management and conservation. We used genetic mark-recapture-recovery to derive estimates of abundance and survival for the Baffin Bay (BB) polar bear subpopulation — the first time this method has been used successfully for this species. Genetic data from tissue samples we collected via biopsy darting were combined with historical physical capture and harvest recovery data. The combined data set consisted of 1410 genetic samples (2011–2013), 914 physical captures (1993–1995, 1997), and 234 harvest returns of marked bears (1993–2013). The estimate of mean subpopulation abundance was 2826 (95% CI = 2284–3367) in 2012–2013. Estimates of annual survival (mean ñ SE) were 0.90 ñ 0.05 and 0.78 ñ 0.06 for females and males age >= 2 yr, respectively. The proportion of total mortality of adult females and males that was attributed to legal harvest was 0.16 ñ 0.05 and 0.26 ñ 0.06, respectively. Remote sensing sea-ice data, telemetry data, and spatial distribution of onshore sampling indicated that polar bears were more likely to use offshore sea-ice habitat during the 1990s sampling period compared to the 2010s. Furthermore, in the 1990s, sampling of deep fjords and inland areas was limited, and no offshore sampling occurred in either time period, which precluded comparisons of abundance between the 1993–1997 and 2011–2013 study periods. Our findings demonstrate that genetic sampling can be a practical method for demographic assessment of polar bears over large spatial and temporal scales.

Modeling ringed seal Pusa hispida habitat and lair emergence timing in the eastern Bering and Chukchi seas

Lindsay, J.M., K.L. Laidre, P.B. Conn, E.E. Moreland, and P.L. Boveng, "Modeling ringed seal Pusa hispida habitat and lair emergence timing in the eastern Bering and Chukchi seas," Endanger. Species Res., 46, doi:10.3354/esr01140 , 2021.

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9 Sep 2021

Ringed seals Pusa hispida are reliant on snow and sea ice for denning, and a better understanding of ringed seal habitat selection and timing of emergence from snow dens (also called lairs) is needed to quantify and predict effects of climate change in the Arctic. We used generalized additive models to assess relationships between ringed seal counts, from spring aerial surveys in the Bering Sea (2012 and 2013) and Chukchi Sea (2016), and spatiotemporal covariates including survey date, remotely sensed snow and sea-ice values, and short-term weather data. We produced separate models for total ringed seal counts and for pup counts within each region. Our models showed that in both areas, total ringed seal counts increased over the course of the spring, especially after 15 May, indicating emergence from lairs and/or the onset of basking behavior. For the more northerly Chukchi Sea, we found a substantial unimodal effect of snow melt progression and a positive effect of snow depth on total ringed seal counts. In contrast, Bering Sea total ringed seal counts and pup counts in both regions were affected much more strongly by date than by habitat variables. Overall, our findings demonstrate that snow depth and melt play an important role in the timing of ringed seal den emergence, particularly in the Chukchi Sea, and suggest that ringed seal denning may be affected by continued shifts in melt and snow depth associated with climate change.

Vertical sonar beam width and scanning behavior of wild belugas (Delphinapterus leucas) in West Greenland

Zahn, M.J., K.L. Laidre, P. Still, M.H. Rasmussen, and J.C. Koblitz, "Vertical sonar beam width and scanning behavior of wild belugas (Delphinapterus leucas) in West Greenland," PLOS One, 16, doi:10.1371/journal.pone.0257054, 2021.

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9 Sep 2021

Echolocation signals of wild beluga whales (Delphinapterus leucas) were recorded in 2013 using a vertical, linear 16-hydrophone array at two locations in the pack ice of Baffin Bay, West Greenland. Individual whales were localized for 4:42 minutes of 1:04 hours of recordings. Clicks centered on the recording equipment (i.e. on-axis clicks) were isolated to calculate sonar parameters. We report the first sonar beam estimate of in situ recordings of wild belugas with an average –3 dB asymmetrical vertical beam width of 5.4°, showing a wider ventral beam. This narrow beam width is consistent with estimates from captive belugas; however, our results indicate that beluga sonar beams may not be symmetrical and may differ in wild and captive contexts. The mean apparent source level for on-axis clicks was 212 dB pp re 1 µPa and whales were shown to vertically scan the array from 120 meters distance. Our findings support the hypothesis that highly directional sonar beams and high source levels are an evolutionary adaptation for Arctic odontocetes to reduce unwanted surface echoes from sea ice (i.e., acoustic clutter) and effectively navigate through leads in the pack ice (e.g., find breathing holes). These results provide the first baseline beluga sonar metrics from free-ranging animals using a hydrophone array and are important for acoustic programs throughout the Arctic, particularly for acoustic classification between belugas and narwhals (Monodon monoceros).

Accelerated sea ice loss in the Wandel Sea points to a change in the Arctic's Last Ice Area

Schweiger, A.J., M. Steele, J. Zhang, G.W.K. Moore, and K.L. Laidre, "Accelerated sea ice loss in the Wandel Sea points to a change in the Arctic's Last Ice Area," Comm. Earth Environ., 2, doi:, 2021.

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1 Jul 2021

The Arctic Ocean's Wandel Sea is the easternmost sector of the Last Ice Area, where thick, old sea ice is expected to endure longer than elsewhere. Nevertheless, in August 2020 the area experienced record-low sea ice concentration. Here we use satellite data and sea ice model experiments to determine what caused this record sea ice minimum. In our simulations there was a multi-year sea-ice thinning trend due to climate change. Natural climate variability expressed as wind-forced ice advection and subsequent melt added to this trend. In spring 2020, the Wandel Sea had a mixture of both thin and — unusual for recent years — thick ice, but this thick ice was not sufficiently widespread to prevent the summer sea ice concentration minimum. With continued thinning, more frequent low summer sea ice events are expected. We suggest that the Last Ice Area, an important refuge for ice-dependent species, is less resilient to warming than previously thought.

Do wild polar bears (Ursus maritimus) use tools when hunting walruses (Odobenus rosmarus)?

Stirling, I., K.L. Laidre, and E.W. Born, "Do wild polar bears (Ursus maritimus) use tools when hunting walruses (Odobenus rosmarus)?" Arctic, 74, 175-187, doi:10.14430/arctic72532, 2021.

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8 Jun 2021

Since the late 1700s, reports of polar bears (Ursus maritimus) using tools (i.e., pieces of ice or stones) to kill walruses (Odobenus rosmarus) have been passed on verbally to explorers and naturalists by their Inuit guides, based on local traditional ecological knowledge (TEK) as well as accounts of direct observations or interpretations of tracks in the snow made by the Inuit hunters who reported them. To assess the possibility that polar bears may occasionally use tools to hunt walruses in the wild, we summarize 1) observations described to early explorers and naturalists by Inuit hunters about polar bears using tools, 2) more recent documentation in the literature from Inuit hunters and scientists, and 3) recent observations of a polar bear in a zoo spontaneously using tools to access a novel food source. These observations and previously published experiments on brown bears (Ursus arctos) confirm that, in captivity, polar and brown bears are both capable of conceptualizing the use of a tool to obtain a food source that would otherwise not be accessible. Based on the information from all our sources, this may occasionally also have been the case in the wild. We suggest that possible tool use by polar bears in the wild is infrequent and mainly limited to hunting walruses because of their large size, difficulty to kill, and their possession of potentially lethal weapons for both their own defense and the direct attack of a predator.

Reconciling behavioral, bioenergetic, and oceanographic views of bowhead whale predation on overwintering copepods at an Arctic hotspot (Disko Bay, Greenland)

Banas, N.S., E.F. Møller, K.L. Laidre, M. Simon, I.H. Ellingsen, and T.G. Nielsen, "Reconciling behavioral, bioenergetic, and oceanographic views of bowhead whale predation on overwintering copepods at an Arctic hotspot (Disko Bay, Greenland)," Front. Mar. Sci., 8, doi:10.3389/fmars.2021.614582, 2021.

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26 May 2021

Bowhead whales (Balaena mysticetus) visit Disko Bay, West Greenland in winter and early spring to feed on Calanus spp., at a time of year when the copepods are still mostly in diapause and concentrated in near-bottom patches. Combining past observations of copepod abundance and distribution with detailed observations of bowhead whale foraging behaviour from telemetry suggests that if the whales target the highest-density patches, they likely consume 26–75% of the Calanus standing stock annually. A parallel bioenergetic calculation further suggests that the whales' patch selection must be close to optimally efficient at finding hotspots of high density copepods near the sea floor in order for foraging in Disko Bay to be a net energetic gain. Annual Calanus consumption by bowhead whales is similar to median estimates of consumption by each of three zooplankton taxa (jellies, chaetognaths, and predatory copepods), and much greater than the median estimate of consumption by fish larvae, as derived from seasonal abundance and specific ingestion rates from the literature. The copepods' self-concentration during diapause, far from providing a refuge from predation, is the behaviour that makes this strong trophic link possible. Because the grazing impact of the whales comes 6–10 months later than the annual peak in primary production, and because Disko Bay sits at the end of rapid advective pathways (here delineated by a simple numerical particle-tracking experiment), it is likely that these Calanus populations act in part as a long-distance energetic bridge between the whales and primary production hundreds or thousands of km away.

Marine mammal hotspots in the Greenland and Barents seas

Hamilton, C.D., and 22 others including K.L. Laidre, "Marine mammal hotspots in the Greenland and Barents seas," Mar. Ecol. Prog. Ser., 659, 3-28, doi:10.3354/meps13584, 2021.

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4 Feb 2021

Environmental change and increasing levels of human activity are threats to marine mammals in the Arctic. Identifying marine mammal hotspots and areas of high species richness are essential to help guide management and conservation efforts. Herein, space use based on biotelemetric tracking devices deployed on 13 species (ringed seal Pusa hispida, bearded seal Erignathus barbatus, harbour seal Phoca vitulina, walrus Odobenus rosmarus, harp seal Pagophilus groenlandicus, hooded seal Cystophora cristata, polar bear Ursus maritimus, bowhead whale Balaena mysticetus, narwhal Monodon monoceros, white whale Delphinapterus leucas, blue whale Balaenoptera musculus, fin whale Balaenoptera physalus and humpback whale Megaptera novaeangliae; total = 585 individuals) in the Greenland and northern Barents Seas between 2005 and 2018 is reported. Getis-Ord G_I* hotspots were calculated for each species as well as all species combined, and areas of high species richness were identified for summer/autumn (Jun-Dec), winter/spring (Jan-May) and the entire year. The marginal ice zone (MIZ) of the Greenland Sea and northern Barents Sea, the waters surrounding the Svalbard Archipelago and a few Northeast Greenland coastal sites were identified as key marine mammal hotspots and areas of high species richness in this region. Individual hotspots identified areas important for most of the tagged animals, such as common resting, nursing, moulting and foraging areas. Location hotspots identified areas heavily used by segments of the tagged populations, including denning areas for polar bears and foraging areas. The hotspots identified herein are also important habitats for seabirds and fishes, and thus conservation and management measures targeting these regions would benefit multiple groups of Arctic animals.

Habitat features predict carrying capacity of a recovering marine carnivore

Tinker, M.T., and 9 others including K.L. Laidre, "Habitat features predict carrying capacity of a recovering marine carnivore," J. Wildl. Manage., 85, 303-323, doi:, 2021.

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1 Feb 2021

The recovery of large carnivore species from overâ€exploitation can have socioecological effects; thus, reliable estimates of potential abundance and distribution represent a valuable tool for developing management objectives and recovery criteria. For sea otters (Enhydra lutris), as with many apex predators, equilibrium abundance is not constant across space but rather varies as a function of local habitat quality and resource dynamics, thereby complicating the extrapolation of carrying capacity (K) from one location to another. To overcome this challenge, we developed a stateâ€space model of densityâ€dependent population dynamics in southern sea otters (E. l. nereis), in which K is estimated as a continuously varying function of a suite of physical, biotic, and oceanographic variables, all described at fine spatial scales. We used a thetaâ€logistic process model that included environmental stochasticity and allowed for densityâ€independent mortality associated with shark bites. We used Bayesian methods to fit the model to time series of survey data, augmented by auxiliary data on cause of death in stranded otters. Our model results showed that the expected density at K for a given area can be predicted based on local bathymetry (depth and distance from shore), benthic substrate composition (rocky vs. soft sediments), presence of kelp canopy, net primary productivity, and whether or not the area is inside an estuary. In addition to densityâ€dependent reductions in growth, increased levels of sharkâ€bite mortality over the last decade have also acted to limit population expansion. We used the functional relationships between habitat variables and equilibrium density to project estimated values of K for the entire historical range of southern sea otters in California, USA, accounting for spatial variation in habitat quality. Our results suggest that California could eventually support 17,226 otters (95% CrIâ€‰=â€‰9,739–30,087). We also used the fitted model to compute candidate values of optimal sustainable population abundance (OSP) for all of California and for regions within California. We employed a simulationâ€based approach to determine the abundance associated with the maximum net productivity level (MNPL) and propose that the upper quartile of the distribution of MNPL estimates (accounting for parameter uncertainty) represents an appropriate threshold value for OSP. Based on this analysis, we suggest a candidate value for OSP (for all of California) of 10,236, which represents 59.4% of projected K.

Transient benefits of climate change for a high-Arctic polar bear (Ursus maritimus) subpopulation

Laidre, K.L., S.N. Atkinson, E.V. Regehr, H.L. Stern, E.W. Born, Ø. Wiig, N.J. Lunn, M Dyck, P. Heagerty, B.R. Cohen, "Transient benefits of climate change for a high-Arctic polar bear (Ursus maritimus) subpopulation," Global Change Biol., 26, 6251-6265, doi:10.1111/gcb.15286, 2020.

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1 Nov 2020

Kane Basin (KB) is one of the world's most northerly polar bear (Ursus maritimus) subpopulations, where bears have historically inhabited a mix of thick multiyear and annual sea ice yearâ€round. Currently, KB is transitioning to a seasonally iceâ€free region because of climate change. This ecological shift has been hypothesized to benefit polar bears in the nearâ€term due to thinner ice with increased biological production, although this has not been demonstrated empirically. We assess seaâ€ice changes in KB together with changes in polar bear movements, seasonal ranges, body condition, and reproductive metrics obtained from capture–recapture (physical and genetic) and satellite telemetry studies during two study periods (1993–1997 and 2012–2016). The annual cycle of seaâ€ice habitat in KB shifted from a yearâ€round ice platform (~50% coverage in summer) in the 1990s to nearly complete meltâ€out in summer (<5% coverage) in the 2010s. The mean duration between seaâ€ice retreat and advance increased from 109 to 160 days (p = .004). Between the 1990s and 2010s, adult female (AF) seasonal ranges more than doubled in spring and summer and were significantly larger in all months. Body condition scores improved for all ages and both sexes. Mean litter sizes of cubsâ€ofâ€theâ€year (C0s) and yearlings (C1s), and the number of C1s per AF, did not change between decades. The date of spring seaâ€ice retreat in the previous year was positively correlated with C1 litter size, suggesting smaller litters following years with earlier seaâ€ice breakup. Our study provides evidence for range expansion, improved body condition, and stable reproductive performance in the KB polar bear subpopulation. These changes, together with a likely increasing subpopulation abundance, may reflect the shift from thick, multiyear ice to thinner, seasonal ice with higher biological productivity. The duration of these benefits is unknown because, under unmitigated climate change, continued seaâ€ice loss is expected to eventually have negative demographic and ecological effects on all polar bears.

The impact of rising sea temperatures on an Arctic top predator, the narwhal

Chambault, P., and 13 others including K.L. Laidre, "The impact of rising sea temperatures on an Arctic top predator, the narwhal," Sci. Rep., 10, 18678, doi:10.1038/s41598-020-75658-6, 2020.

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29 Oct 2020

Arctic top predators are expected to be impacted by increasing temperatures associated with climate change, but the relationship between increasing sea temperatures and population dynamics of Arctic cetaceans remains largely unexplored. Narwhals (Monodon monoceros) are considered to be among the most sensitive of Arctic endemic marine mammals to climate change due to their limited prey selection, strict migratory patterns and high site fidelity. In the context of climate change, we assume that the population dynamics of narwhals are partly influenced by changes in environmental conditions, with warm areas of increasing sea temperatures having lower abundance of narwhals. Using a unique large dataset of 144 satellite tracked narwhals, sea surface temperature (SST) data spanning 25 years (1993–2018) and narwhal abundance estimates from 17 localities, we (1) assessed the thermal exposure of this species, (2) investigated the SST trends at the summer foraging grounds, and (3) assessed the relationship between SST and abundance of narwhals. We showed a sharp SST increase in Northwest, Mideast and Southeast Greenland, whereas no change could be detected in the Canadian Arctic Archipelago (CAA) and in the Greenland Sea. The rising sea temperatures were correlated with the smallest narwhal abundance observed in the Mideast and Southeast Greenland (<â€‰2000 individuals), where the mean summer sea temperatures were the highest (6.3°C) compared to the cold waters of the CAA (0.7°C) that were associated with the largest narwhal populations (>â€‰40,000 individuals). These results support the hypothesis that warming ocean waters will restrict the habitat range of the narwhal, further suggesting that narwhals from Mideast and Southeast Greenland may be under pressure to abandon their traditional habitats due to ocean warming, and consequently either migrate further North or locally go extinct.

Seasonal detections of bearded seal (Erignathus barbatus) vocalizations in Baffin Bay and Davis Strait in relation to sea ice concentration

Boye, T.K., M.J. Simon, K.L. Laidre, F. Rignét, and K.M. Stafford, "Seasonal detections of bearded seal (Erignathus barbatus) vocalizations in Baffin Bay and Davis Strait in relation to sea ice concentration," Polar Biol., 43, 1493-1502, doi:10.1007/s00300-020-02723-1, 2020.

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8 Aug 2020

There is limited information about the biology and seasonal distribution of bearded seals (Erignathus barbatus) in Greenland. The species is highly ice-associated and depends on sea ice for hauling out and giving birth, making it vulnerable to climate change. We investigated the seasonality and distribution of bearded seal vocalizations at seven different locations across southern Baffin Bay and Davis Strait, West Greenland. Aural M2 and HARUphone recorders were deployed on the sea bottom during 2006–2007 and 2011–2013. Recordings were analyzed for presence/absence of bearded seal calls relative to location (including distance to shore and depth), mean sea ice concentration and diel patterns. Calling occurred between November and late June with most intense calling during the mating season at all sites. There was a clear effect of depth and distance to shore on the number of detections, and the Greenland shelf (<â€‰300 m) appeared to be the preferred habitat for bearded seals during the mating season. These results suggest that bearded seals may retreat with the receding sea ice to Canada during summer or possibly spend the summer along the West Greenland coast. It is also possible that, due to seasonal changes in bearded seal vocal behavior, animals may have been present in our study area in summer, but silent. The number of detections was affected by the timing of sea ice formation but not sea ice concentration. Diel patterns were consistent with patterns found in other parts of the Arctic, with a peak during early morning (0400 local) and a minimum during late afternoon (1600 local). While vocalization studies have been conducted on bearded seals in Norwegian, Canadian, northwest Greenland, and Alaskan territories, this study fills the gap between these areas.

Grounded icebergs as maternity denning habitat for polar bears (Ursus maritimus) in North and Northeast Greenland

Laidre, K.L., and I. Stirling, "Grounded icebergs as maternity denning habitat for polar bears (Ursus maritimus) in North and Northeast Greenland," Polar Biol., 43, 937-943, doi:10.1007/s00300-020-02695-2, 2020.

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1 Jul 2020

This study provides the first documentation of polar bear (Ursus maritimus) maternity denning in snowdrifts around icebergs frozen into the fast ice or grounded on the seafloor. Based on six den observations in north and northeast Greenland during spring surveys in 2018 and 2019 (109 flight hours), together with observations of 20 adult females with 35 cubs of the year (COYs) in adjacent sea ice, we hypothesize that the use of snowdrifts around icebergs for maternity denning is an established behavior in the region and not a random event. Factors influencing maternity denning in snowdrifts around icebergs may include limited suitable drifts on the nearby terrestrial polar desert due to low precipitation, the presence of suitable wind-blown snow banks regardless of the direction of autumn storm winds, cold and stable habitat throughout the winter denning period, and access to ringed seal (Pusa hispida) pupping habitat in the nearby Northeast Water polynya. This type of maternity denning habitat is only available in glaciated regions of the Arctic where marine-terminating glaciers deposit mélange large enough to become grounded offshore and remain in place for months or years. This habitat may become less stable or disappear with long-term climate warming.

Interrelated ecological impacts of climate change on an apex predator

Laidre, K.L., S. Atkinson, E.V. Regehr, H.L. Stern, E.W. Born, Ø. Wiig, N.J. Lunn, and M. Dyck, "Interrelated ecological impacts of climate change on an apex predator," Ecol. Appl., 30, e02071, doi:10.1002/eap.2071, 2020.

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1 Jun 2020

Climate change has broad ecological implications for species that rely on sensitive habitats. For some top predators, loss of habitat is expected to lead to cascading behavioral, nutritional, and reproductive changes that ultimately accelerate population declines. In the case of the polar bear (Ursus maritimus), declining Arctic sea ice reduces access to prey and lengthens seasonal fasting periods. We used a novel combination of physical capture, biopsy darting, and visual aerial observation data to project reproductive performance for polar bears by linking sea ice loss to changes in habitat use, body condition (i.e., fatness), and cub production. Satellite telemetry data from 43 (1991–1997) and 38 (2009–2015) adult female polar bears in the Baffin Bay subpopulation showed that bears now spend an additional 30 d on land (90 d in total) in the 2000s compared to the 1990s, a change closely correlated with changes in spring sea ice breakup and fall sea ice formation. Body condition declined for all sex, age, and reproductive classes and was positively correlated with sea ice availability in the current and previous year. Furthermore, cub litter size was positively correlated with maternal condition and spring breakup date (i.e., later breakup leading to larger litters), and negatively correlated with the duration of the iceâ€free period (i.e., longer iceâ€free periods leading to smaller litters). Based on these relationships, we projected reproductive performance three polar bear generations into the future (approximately 35 yr). Results indicate that twoâ€cub litters, previously the norm, could largely disappear from Baffin Bay as sea ice loss continues. Our findings demonstrate how concurrent analysis of multiple data types collected over long periods from polar bears can provide a mechanistic understanding of the ecological implications of climate change. This information is needed for longâ€term conservation planning, which includes quantitative harvest risk assessments that incorporate estimated or assumed trends in future environmental carrying capacity.

Variability in fin whale (Balaenoptera physalus) occurrence in the Bering Strait and southern Chukchi Sea in relation to environmental factors

Escajeda, E., K.M. Stafford, R.A. Woodgate, K.L. Laidre, "Variability in fin whale (Balaenoptera physalus) occurrence in the Bering Strait and southern Chukchi Sea in relation to environmental factors," Deep Sea Res. II, 177, doi:0.1016/j.dsr2.2020.104782, 2020.

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4 May 2020

Fin whales (Balaenoptera physalus) are common summer visitors to the Pacific Arctic, migrating through the Bering Strait and into the southern Chukchi Sea to feed on seasonally-abundant prey. The abundance and distribution of fin whales in the Chukchi Sea varies from year-to-year, possibly reflecting fluctuating environmental conditions. We hypothesized that fin whale calls were most likely to be detected in years and at sites where productive water masses were present, indicated by low temperatures and high salinities, and where strong northward water and wind velocities, resulting in increased prey advection, were prevalent. Using acoustic recordings from three moored hydrophones in the Bering Strait region from 2009–2015, we identified fin whale calls during the open-water season (July–November) and investigated potential environmental drivers of interannual variability in fin whale presence. We examined near-surface and near-bottom temperatures (T) and salinities (S), wind and water velocities through the strait, water mass presence as estimated using published T/S boundaries, and satellite-derived sea surface temperatures and sea-ice concentrations. Our results show significant interannual variability in the acoustic presence of fin whales with the greatest detections of calls in years with contrasting environmental conditions (2012 and 2015). Colder temperatures, lower salinities, slower water velocities, and weak southward winds prevailed in 2012 while warmer temperatures, higher salinities, faster water velocities, and moderate southward winds prevailed in 2015. Most detections (96%) were recorded at the mooring site nearest the confluence of the nutrient-rich Anadyr and Bering Shelf water masses, ~35 km north of Bering Strait, indicating that productive water masses may influence the occurrence of fin whales. The disparity in environmental conditions between 2012 and 2015 suggests there may be multiple combinations of environmental factors or other unexamined variables that draw fin whales into the Pacific Arctic.

The ecological and behavioral significance of short-term food caching in polar bears (Ursus maritimus)

Stirling, I., K.L. Laidre, A.E. Derocher, and R. Van Meurs, "The ecological and behavioral significance of short-term food caching in polar bears (Ursus maritimus)," Arctic Sci., 6, 41-52, doi:10.1139/as-2019-0008, 2020.

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1 Mar 2020

The paucity of observations of wild polar bears (Ursus maritimus) caching of food (including hoarding, i.e., burying and remaining with a kill for up to a few days) has led to the conclusion that such behavior does not occur or is negligible in this species. We document 19 observations of short-term hoarding by polar bears between 1973 and 2018 in Svalbard, Greenland, and Canada. Short-term hoarding appears to be influenced by size of the kill and its remaining energetic value after the first meal has been consumed. Fat and meat from smaller seals, such as pup or yearling ringed seals (Pusa hispida), are largely devoured immediately, leaving little to hoard. Carcasses of adult ringed seals, harp seals (Pagophilus groenlandicus), and bearded seals (Erignathus barbatus) may be covered with snow to reduce the chance of kleptoparasitism by another bear or other scavengers visually detecting a dark spot on the ice, while the hoarding bear lies nearby. Hoarding of other species, such as beluga (Delphinapterus leucas) (calves or parts) or other polar bears, appears opportunistic. We review differences in caching, including short-term hoarding behavior between polar bears and brown bears (U. arctos), and hypothesize about factors that may have influenced their evolution.

The polar regions in a 2°C warmer world

Post, E., and 14 others including K.L. Laidre, "The polar regions in a 2°C warmer world," Sci. Adv., 5, doi:10.1126/sciadv.aaw9883, 2019.

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4 Dec 2019

Over the past decade, the Arctic has warmed by 0.75°C, far outpacing the global average, while Antarctic temperatures have remained comparatively stable. As Earth approaches 2°C warming, the Arctic and Antarctic may reach 4°C and 2°C mean annual warming, and 7°C and 3°C winter warming, respectively. Expected consequences of increased Arctic warming include ongoing loss of land and sea ice, threats to wildlife and traditional human livelihoods, increased methane emissions, and extreme weather at lower latitudes. With low biodiversity, Antarctic ecosystems may be vulnerable to state shifts and species invasions. Land ice loss in both regions will contribute substantially to global sea level rise, with up to 3 m rise possible if certain thresholds are crossed. Mitigation efforts can slow or reduce warming, but without them northern high latitude warming may accelerate in the next two to four decades. International cooperation will be crucial to foreseeing and adapting to expected changes.

Influence of occupation history and habitat on Washington sea otter diet

Hale, J.R., K.L. Laidre, M.T. Tinker, R.J. Jameson, S.J. Jeffries, S.E. Larson, and J.L. Bodkin, "Influence of occupation history and habitat on Washington sea otter diet," Mar. Mammal Sci., 34, 1369-1395, doi:10.1111/mms.12598, 2019.

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27 Mar 2019

Habitat characteristics are primary determinants of nearshore marine communities. However, biological drivers like predation can also be important for community composition. Sea otters (Enhydra lutris ssp.) are a salient example of a keystone species exerting topâ€down control on ecosystem community structure. The translocation and subsequent population growth and range expansion of the northern sea otter (Enhydra lutris kenyoni) in Washington State over the last five decades has created a spatioâ€temporal gradient in sea otter occupation time and density, and acts as a natural experiment to quantify how sea otter population status and habitat type influence sea otter diet. We collected focal observations of sea otters foraging at sites across the gradient in varying habitat types between 2010 and 2017. We quantified sea otter diet composition and diversity, and longâ€term rates of energy gain across the gradient. We found that sea otter diet diversity was positively correlated with cumulative sea otter density, while rate of energy gain was negatively correlated with cumulative density. Additionally, we found that habitat type explained 1.77 times more variance in sea otter diet composition than sea otter cumulative density. Longâ€term diet studies can provide a broader picture of sea otter population status in Washington State.

Variation in non-metrical skull traits of polar bears (Ursus maritimus) and relationships across East Greenland and adjacent subpopulations (1830–2013)

Wiig, Ø., P. Henrichsen, T. Sjøvold, E.W. Born, K.L. Laidre, R. Dietz, C. Sonne, and J. Aars, "Variation in non-metrical skull traits of polar bears (Ursus maritimus) and relationships across East Greenland and adjacent subpopulations (1830–2013)," Polar Biol., 42, 461-474, doi:10.1007/s00300-018-2435-x, 2019.

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1 Mar 2019

Knowledge of subpopulation identity including substructure is a prerequisite for sound management of polar bears (Ursus maritimus). It is not known whether the present catch of polar bears in the East Greenland subpopulation (EG) is sustainable. We used the Mean Measure of Divergence (MMD) to examine geographical variation in non-metrical traits from 1414 polar bear (Ursus maritimus) skulls collected in East Greenland (EG), Svalbard (SVA), Franz Josef Land (FJL), Davis Strait (DS), Baffin Bay (BB), and Kane Basin (KB), between 1830 and 2013. We focused on East Greenland with the goal of examining substructuring in the subpopulation. We did not find significant differences among samples across four areas of the EG subpopulation (i.e., offshore Fram Strait, NE, SE, and SW Greenland) using data from 1830 to 1983. Our analyses did not lend support to substructuring. However, we draw our conclusions with caution because skulls were sampled over a long time period and had low power due to small sample sizes. Also, comparisons were limited to pre-1980s skulls. The decrease in sea ice in EG since the 1990s due to climate change may have led to substructuring not detected with MMD. This study contributes to the current efforts by Greenland authorities to quantify connectivity of polar bears between southeast and northeast Greenland which is important information for the evaluation of the sustainability of the catch of bears from the EG subpopulation.

Survey-based assessment of the frequency and potential impacts of recreation on polar bears

Rode, K.D., and 12 others including K.L. Laidre, "Survey-based assessment of the frequency and potential impacts of recreation on polar bears," Biol. Conserv., 227, 121-132, doi:10.1016/j.biocon.2018.09.008, 2018.

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1 Nov 2018

Conservation plans for polar bears (Ursus maritimus) typically cannot prescribe management actions to address their primary threat: sea ice loss associated with climate warming. However, there may be other stressors that compound the negative effects of sea ice loss which can be mitigated. For example, Arctic tourism has increased concurrent with polar bears increasingly using terrestrial habitats, which creates the potential for increased human-bear interactions. Little is known about the types, frequency, or potential impacts of recreation. We conducted a Delphi survey among experts who live and work in polar bear habitats, followed by an internet-based survey to which 47 managers, tour operators, community members, and scientists contributed. Participants identified viewing-based recreation as increasing and affecting the largest proportion of bears within subpopulations that come ashore during the ice-free season. Survey respondents suggested that negative effects of viewing, including displacement and habituation, could be reduced by restricting human use areas and distances between bears and people. Killing of bears in defense was associated more with camping or hunting for other species than other recreations, and may be mitigated with deterrents. Snowmobiling was the most common recreation across the polar bears' range, and reportedly caused some den abandonment and displacement. However, respondents estimated that <10% of polar bears are exposed to most types of recreation and <50% surmised any negative impacts. Nevertheless, mitigating some of the negative impacts identified in this study may become increasingly important as polar bears cope with sea ice loss.

Historical and potential future importance of large whales as food for polar bears

Laidre, K.L., I. Stirling, J.A. Estes, A. Kochnev, and J. Roberts, "Historical and potential future importance of large whales as food for polar bears," Front. Ecol. Environ., 16, 515-524, doi:10.1002/fee.1963, 2018.

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9 Oct 2018

Polar bears (Ursus maritimus) are expected to be adversely impacted by a warming Arctic due to melting of the seaâ€ice platform from which they hunt iceâ€breeding seals. We evaluated the hypothesis that scavenging on stranded large whale carcasses may have facilitated polar bear survival through past interglacial periods during which seaâ€ice was limited by analyzing: (1) presentâ€day scavenging by polar bears on large whale carcasses; (2) energy values of large whale species; and (3) the ability of polar bears, like the brown bears (Ursus arctos) from which they evolved, to quickly store large amounts of lipids and to fast for extended periods. We concluded that scavenging on large whale carcasses likely facilitated survival of polar bears in past interglacial periods when access to seals was reduced. In a future, iceâ€impoverished Arctic, whale carcasses are less likely to provide nutritional refuge for polar bears because overharvesting by humans has greatly reduced large whale populations, carcass availability is geographically limited, and climateâ€induced seaâ€ice loss is projected to occur at a more rapid pace than polar bears have experienced at any previous time in their evolutionary history.

Prevalence of antibodies against Brucella app. in West Greenland polar bears (Ursus maritimus) and East Greenland muskoxen (Ovibos moschatus)

Sonne, C., and 21 others including K. Laidre, "Prevalence of antibodies against Brucella app. in West Greenland polar bears (Ursus maritimus) and East Greenland muskoxen (Ovibos moschatus)," Polar Biol., 41, 1671â€“1680, doi:10.1007/s00300-018-2307-4, 2018.

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1 Sep 2018

Zoonotic infections transmitted from terrestrial and marine mammals to humans in European Arctic are of unknown significance, despite considerable potential for transmission due to local hunt and a rapidly changing environment. As an example, infection with Brucella bacteria may have significant impact on human health due to consumption of raw meat or otherwise contact with tissues and fluids of infected game species such as muskoxen and polar bears. Here, we present serological results for Baffin Bay polar bears (Ursus maritimus) (nâ€‰=â€‰96) and North East Greenland muskoxen (Ovibos moschatus) (nâ€‰=â€‰32) for antibodies against Brucella spp. The analysis was a two-step trial initially using the Rose Bengal Test (RBT), followed by confirmative competitive enzyme-linked immunosorbent assays of RBT-positive samples. No muskoxen had antibodies against Brucella spp., while antibodies were detected in six polar bears (6.25%) rendering a seroprevalence in line with previous findings in other Arctic regions. Seropositivity was not related to sex, age or biometrics i.e. size and body condition. Whether Brucella spp. antibodies found in polar bears were due to either prey spill over or true recurrent Brucella spp. infections is unknown. Our results therefore highlight the importance of further research into the zoonotic aspects of Brucella spp. infections, and the impact on wildlife and human health in the Arctic region.

Vulnerability of arctic marine mammals to vessel traffic in the increasingly ice-free Northwest Passage and Northern Sea Route

Hauser, D.D.W., K.L. Laidre, and H.L. Stern, "Vulnerability of arctic marine mammals to vessel traffic in the increasingly ice-free Northwest Passage and Northern Sea Route," Proc. Nat. Acad. Sci. USA, 115, 7617-7622, doi:10.1073/pnas.1803543115, 2018

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2 Jul 2018

The fabled Northwest Passage and Northern Sea Route that were once the quests of early Western explorers are now increasingly sea iceâ€“free, with routine vessel transits expected by midcentury. The potential impacts of this novel vessel traffic on endemic Arctic marine mammal (AMM) species are unknown despite their critical social and ecological roles in the ecosystem and widely recognized susceptibility to ice loss. We developed a vulnerability assessment of 80 subpopulations of seven AMM species to vessel traffic during the ice-free season. Vulnerability scores were based on the combined influence of spatially explicit exposure to the sea routes and a suite of sensitivity variables. More than half of AMM subpopulations (42/80) are exposed to open-water vessel transits in the Arctic sea routes. Narwhals (Monodon monoceros) were estimated to be most vulnerable to vessel impacts, given their high exposure and sensitivity, and polar bears (Ursus maritimus) were estimated to be the least vulnerable because of their low exposure and sensitivity. Regions with geographic bottlenecks, such as the Bering Strait and eastern Canadian Arctic, were characterized by two to three times higher vulnerability than more remote regions. These pinch points are obligatory pathways for both vessels and migratory AMMs, and so represent potentially high conflict areas but also opportunities for conservation-informed planning. Some of the species and regions identified as least vulnerable were also characterized by high uncertainty, highlighting additional data and monitoring needs. Our quantification of the heterogeneity of risk across AMM species provides a necessary first step toward developing best practices for maritime industries poised to advance into this rapidly changing seascape.

Sea surface temperature predicts the movements of an Arctic cetacean: The bowhead whale

Chambault, P., C.M. Albertsen, T.A. Patterson, R.G. Hanson, O. Tervo, K.L. Laidre, and M.P. Heide-Jørgensen, "Sea surface temperature predicts the movements of an Arctic cetacean: The bowhead whale," Sci. Rep., 8, 9698, doi:10.1038/s41598-018-27966-1, 2018.

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25 Jun 2018

The effects of climate change constitute a major concern in Arctic waters due to the rapid decline of sea ice, which may strongly alter the movements and habitat availability of Arctic marine mammals. We tracked 98 bowhead whales by satellite over an 11-year period (2001–2011) in Baffin Bay — West Greenland to investigate the environmental drivers (specifically sea surface temperature and sea ice) involved in bowhead whaleâ€™s movements. Movement patterns differed according to season, with aggregations of whales found at higher latitudes during spring and summer likely in response to sea-ice retreat and increasing sea temperature (SST) facilitated by the warm West Greenland Current. In contrast, the whales moved further south in response to sea temperature decrease during autumn and winter. Statistical models indicated that the whales targeted a narrow range of SSTs from –0.5 to 2°C. Sea surface temperatures are predicted to undergo a marked increase in the Arctic, which could expose bowhead whales to both thermal stress and altered stratification and vertical transport of water masses. With such profound changes, bowhead whales may face extensive habitat loss. Our results highlight the need for closer investigation and monitoring in order to predict the extent of future distribution changes.

Indirect effects of sea ice loss on summer–fall habitat and behaviour for sympatric populations of an Arctic marine predator

Hauser, D.D.W., K.L. Laidre, H.L. Stern, R.S. Suydam, and P.R. Richard, "Indirect effects of sea ice loss on summer–fall habitat and behaviour for sympatric populations of an Arctic marine predator," Divers. Distrib., 24, 791-799, doi:10.1111/ddi.12722, 2018.

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1 Jun 2018

Climate change is fundamentally altering habitats, with complex consequences for species across the globe. The Arctic has warmed 2–3 times faster than the global average, and unprecedented sea ice loss can have multiple outcomes for iceâ€associated marine predators. Our goal was to assess impacts of sea ice loss on populationâ€specific habitat and behaviour of a migratory Arctic cetacean.

Using satellite telemetry data collected during summer–fall from sympatric beluga whale (Delphinapterus leucas) populations ("Chukchi" and "Beaufort" belugas), we applied generalized estimating equations to evaluate shifts in sea ice habitat associations and diving behaviour during two periods: 1993–2002 ("early") and 2004–2012 ("late"). We used resource selection functions to assess changes in sea ice selection as well as predict trends in habitat selection and "optimal" habitat, based on satelliteâ€derived sea ice data from 1990 to 2014.

Sea ice cover declined substantially between periods, and Chukchi belugas specifically used significantly lower sea ice concentrations during the late than early period. Use of bathymetric features did not change between periods for either population. Populationâ€specific sea ice selection, predicted habitat and the amount of optimal habitat also generally did not change during 1990–2014. Chukchi belugas tracked during 2007–2012 made significantly more longâ€duration and deeper dives than those tracked during 1998–2002.

Taken together, our results suggest bathymetric parameters are consistent predictors of summer–fall beluga habitat rather than selection for specific sea ice conditions during recent sea ice loss. Beluga whales were able to mediate habitat change despite their sea ice associations. However, trends towards prolonged and deeper diving possibly indicate shifting foraging opportunities associated with ecological changes that occur in concert with sea ice loss. Our results highlight that responses by some Arctic marine wildlife can be indirect and variable among populations, which could be included in predictions for the future.

Traditional knowledge about polar bears (Ursus maritimus) in East Greenland: Changes in the catch and climate over two decades

Laidre, K.L., A.D. Northey, and F. Ugarte, "Traditional knowledge about polar bears (Ursus maritimus) in East Greenland: Changes in the catch and climate over two decades," Front. Mar. Sci., 5, 135, doi:10.3389/fmars.2018.00135, 2018.

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11 May 2018

In Greenland, polar bears (Ursus maritimus) are nutritional, economic, and cultural subsistence resources for Inuit. Traditional Ecological Knowledge (TEK) collected from subsistence hunters can provide important insights and improve management decisions when collected systematically. We report on the results of a TEK survey of subsistence polar bear hunters living in the areas around Tasiilaq and Ittoqqortoormiit, East Greenland. Twenty-five full-time polar bear hunters were interviewed between December 2014 and March 2015 in a conversation-style interview, where a local interviewer fluent in the East Greenlandic dialect asked a series of 55 predetermined questions. The primary goals were to (1) gather Inuit perspectives on polar bear subsistence quotas and hunting strategies, (2) understand how climate change is affecting the polar bear subsistence hunt, and (3) document observed changes in polar bear distribution, abundance, and biology. Approximately 40% of the Tasiilaq respondents had caught between 10 and 19 polar bears in their lifetime, while 67% of Ittoqqortoormiit respondents reported lifetime catches of ≥20 bears. In both areas, polar bears were most commonly hunted between February and April. Hunters noted large changes to the climate in the areas where they hunt polar bears. Most hunters reported loss of sea ice, receding glaciers, unstable weather, and warmer temperatures. In Tasiilaq 73% of the hunters said climate changes had affected the polar bear hunt and in Ittoqqortoormiit about 88% of respondents reported the same. Hunters indicated that sea ice loss has created more areas of open water so dog sledges have become unsafe for hunting transportation compared to 10–15 years ago (reported by 100% of hunters in Tasiilaq and 80% in Ittoqqortoormiit). In Ittoqqortoormiit, the distance traveled during polar bear hunting trips has decreased dramatically. In both areas hunters noted that more polar bears are coming into their communities compared to 10–15 years ago (81% of Tasiilaq hunters and 78% of Ittoqqortoormiit hunters) and pointed to the introduction of quotas and loss of sea ice as potential reasons. This study provides an important perspective on the East Greenland subpopulation of polar bears that can be used to direct science questions and inform management.

Range contraction and increasing isolation of a polar bear subpopulation in an era of seaâ€ice loss

Laidre, K.L., E.W. Born, S.N. Atkinson, Ø. Wiig, L.W. Andersen, N.J. Lunn, M. Dyck, E.V. Regehr, R. McGovern, and P. Heagerty, "Range contraction and increasing isolation of a polar bear subpopulation in an era of seaâ€ice loss," Ecol. Evol., 8, 2062-2075, doi:10.1002/ece3.3809, 2018.

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1 Feb 2018

Climate change is expected to result in range shifts and habitat fragmentation for many species. In the Arctic, loss of sea ice will reduce barriers to dispersal or eliminate movement corridors, resulting in increased connectivity or geographic isolation with sweeping implications for conservation. We used satellite telemetry, data from individually marked animals (research and harvest), and microsatellite genetic data to examine changes in geographic range, emigration, and interpopulation connectivity of the Baffin Bay (BB) polar bear (Ursus maritimus) subpopulation over a 25â€year period of seaâ€ice loss. Satellite telemetry collected from n = 43 (1991–1995) and 38 (2009–2015) adult females revealed a significant contraction in subpopulation range size (95% bivariate normal kernel range) in most months and seasons, with the most marked reduction being a 70% decline in summer from 716,000 km² (SE 58,000) to 211,000 km² (SE 23,000) (p < .001). Between the 1990s and 2000s, there was a significant shift northward during the onâ€ice seasons (2.6° shift in winter median latitude, 1.1Â° shift in spring median latitude) and a significant range contraction in the iceâ€free summers. Bears in the 2000s were less likely to leave BB, with significant reductions in the numbers of bears moving into Davis Strait (DS) in winter and Lancaster Sound (LS) in summer. Harvest recoveries suggested both short and longâ€term fidelity to BB remained high over both periods (83–99% of marked bears remained in BB). Genetic analyses using eight polymorphic microsatellites confirmed a previously documented differentiation between BB, DS, and LS; yet weakly differentiated BB from Kane Basin (KB) for the first time. Our results provide the first multiple lines of evidence for an increasingly geographically and functionally isolated subpopulation of polar bears in the context of longâ€term seaâ€ice loss. This may be indicative of future patterns for other polar bear subpopulations under climate change.

Identifying shifts in maternity den phenology and habitat characteristics of polar bears (Ursus maritimus) in Baffin Bay and Kane Basin

Escajeda, E., K.L. Laidre, E.W. Born, Ø. Wiig, S. Atkinson, M. Dyck, S.H. Ferguson, and N.J. Lunn, "Identifying shifts in maternity den phenology and habitat characteristics of polar bears (Ursus maritimus) in Baffin Bay and Kane Basin," Polar Biol., 41, 87-100, doi:10.1007/s00300-017-2172-6, 2017.

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1 Jan 2018

The phenology and habitat selection of polar bear (Ursus maritimus) maternity dens may shift over time in response to changing environmental conditions. We compared maternity den phenology and habitat characteristics using satellite telemetry data from adult female polar bears from the Baffin Bay (BB) (n = 16 dens; 2009–2015) and Kane Basin (KB) subpopulations (n = 3 dens; 2012–2015) to previously published maternity den data from 1991 to 1997 (BB n = 8 dens; KB n = 3 dens). BB maternity denning duration decreased from a mean of 194.1 days (SD = 21.0 days, n = 8) in the 1990s, to a mean of 167.1 days (SD = 27.6 days, n = 16; p = 0.017) in the 2000s. Delayed den entry accounted for shorter denning durations (1990s entry date x = 7 September; 2000s entry date x = 5 October; p = 0.018). For dens habitat characteristics of which could be measured, BB maternity dens in the 2000s occurred at higher elevations (x = 707.0 m, SD = 284.9 m, n = 15; p = 0.003) and greater slopes (x = 23.1°, SD = 7.4°; p = 0.003) than the 1990s (elevation x ± SD = 351.3 ± 194.5 m, n = 8; slope x Â± SD = 11.9 Â± 6.4±). Aspect also significantly differed between the 1990s (x = 51.3±) and 2000s BB maternity dens (x = 199.7±; Watsonâ€™s U2p = 0.042). KB dens were not statistically compared due to low sample size (n = 3 dens in both periods). Shifts in sea ice phenology and snow availability may explain the observed changes.

Projecting marine mammal distribution in a changing climate

Silber, G.K., and 24 others, including K.L. Laidre and K.M. Stafford, "Projecting marine mammal distribution in a changing climate," Front. Mar. Sci., 4, 413, doi:10.3389/fmars.2017.00413, 2017.

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20 Dec 2017

Climate-related shifts in marine mammal range and distribution have been observed in some populations; however, the nature and magnitude of future responses are uncertain in novel environments projected under climate change. This poses a challenge for agencies charged with management and conservation of these species. Specialized diets, restricted ranges, or reliance on specific substrates or sites (e.g., for pupping) make many marine mammal populations particularly vulnerable to climate change. High-latitude, predominantly ice-obligate, species have experienced some of the largest changes in habitat and distribution and these are expected to continue. Efforts to predict and project marine mammal distributions to date have emphasized data-driven statistical habitat models. These have proven successful for short time-scale (e.g., seasonal) management activities, but confidence that such relationships will hold for multi-decade projections and novel environments is limited. Recent advances in mechanistic modeling of marine mammals (i.e., models that rely on robust physiological and ecological principles expected to hold under climate change) may address this limitation. The success of such approaches rests on continued advances in marine mammal ecology, behavior, and physiology together with improved regional climate projections. The broad scope of this challenge suggests initial priorities be placed on vulnerable species or populations (those already experiencing declines or projected to undergo ecological shifts resulting from climate changes that are consistent across climate projections) and species or populations for which ample data already exist (with the hope that these may inform climate change sensitivities in less well observed species or populations elsewhere). The sustained monitoring networks, novel observations, and modeling advances required to more confidently project marine mammal distributions in a changing climate will ultimately benefit management decisions across time-scales, further promoting the resilience of marine mammal populations.

The commercial harvest of ice-associated seals in the Sea of Okhotsk, 1972-1994

Trukhanova, I.S., A.I. Grachev, A.G. Somov, V.N. Burkanod, K.L. Laidre, and P.L. Boveng, "The commercial harvest of ice-associated seals in the Sea of Okhotsk, 1972-1994," Plos One, 12, doi:10.1371/journal.pone.0182725, 2017.

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10 Aug 2017

Sealing log books from 75 out of 79 commercial harvest cruises carried out between 1972 and 1994 in the Sea of Okhotsk, Russia, were analyzed to describe spatial and temporal allocation of ice-associated seal harvest effort, species composition of catches, total harvest rates, and related parameters for species including ringed (Pusa hispida), ribbon (Histriophoca fasciata), bearded (Erignathus barbatus) and spotted (Phoca largha) seal. Variations in catch per unit effort were explored in relation to year, sea ice conditions, day of the year, and geographic location. In most years, the harvest was predominantly represented by ringed seals (mean = 0.43, range 0.25–0.67), followed by ribbon (mean = 0.31, range 0.15–0.43), spotted (mean = 0.19, range 0.11–0.35) and bearded seals (mean = 0.07, range 0.03–0.14). The struck-and-lost percentages were as high as 30–35% for ringed, bearded and spotted seals and 15–20% for ribbon seals. Catch per unit effort (number of seals/skiff*day) for ringed, ribbon, and spotted seals had a similar seasonal pattern with a distinct spike in catches for spotted seals in the first week of May, for ribbon seals in the last week of May, and for ringed seals in the second week of June. Catches of bearded seals showed a less pronounced temporal structure with a gradual increase toward the end of the harvest season in the majority of years. Spatial distribution of harvest effort followed closely with seal distribution obtained from aerial surveys. These data could be used as a source of information on seal herd location throughout the breeding and molting seasons and for more complex demographic or life-table models. We did not find any evidence of the decline of catch per unit effort over the study period. Timely introduction of state regulations and efficient harvest management apparently prevented severe depletion of ice-associated seal populations in the Sea of Okhotsk during the periods of their intense exploitation.

Decadal shifts in autumn migration timing by Pacific Arctic beluga whales are related to delayed annual sea ice formation

Hauser, D.D.W., K.L. Laidre, K.M. Stafford, H.L. Stern, R.S. Suydam, and P.R. Richard, "Decadal shifts in autumn migration timing by Pacific Arctic beluga whales are related to delayed annual sea ice formation," Global Clim. Change, 23, 2206-2217, doi:10.111/gcb.13564, 2017.

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1 Jun 2017

Migrations are often influenced by seasonal environmental gradients that are increasingly being altered by climate change. The consequences of rapid changes in Arctic sea ice have the potential to affect migrations of a number of marine species whose timing is temporally matched to seasonal sea ice cover. This topic has not been investigated for Pacific Arctic beluga whales (Delphinapterus leucas) that follow matrilineally maintained autumn migrations in the waters around Alaska and Russia. For the sympatric Eastern Chukchi Sea ('Chukchi') and Eastern Beaufort Sea ('Beaufort') beluga populations, we examined changes in autumn migration timing as related to delayed regional sea ice freeze-up since the 1990s, using two independent data sources (satellite telemetry data and passive acoustics) for both populations. We compared dates of migration between 'early' (1993–2002) and 'late' (2004–2012) tagging periods. During the late tagging period, Chukchi belugas had significantly delayed migrations (by 2 to >4 weeks, depending on location) from the Beaufort and Chukchi seas. Spatial analyses also revealed that departure from Beaufort Sea foraging regions by Chukchi whales was postponed in the late period. Chukchi beluga autumn migration timing occurred significantly later as regional sea ice freeze-up timing became later in the Beaufort, Chukchi, and Bering seas. In contrast, Beaufort belugas did not shift migration timing between periods, nor was migration timing related to freeze-up timing, other than for southward migration at the Bering Strait. Passive acoustic data from 2008 to 2014 provided independent and supplementary support for delayed migration from the Beaufort Sea (4 day yr) by Chukchi belugas. Here, we report the first phenological study examining beluga whale migrations within the context of their rapidly transforming Pacific Arctic ecosystem, suggesting flexible responses that may enable their persistence yet also complicate predictions of how belugas may fare in the future.

Correlated velocity models as a fundamental unit of animal movement: Synthesis and applications

Gurarie, E., C.H. Fleming, W.F. Fagan, K.L. Laidre, J. Hernández-Pliego, and O. Ovaskainen, "Correlated velocity models as a fundamental unit of animal movement: Synthesis and applications," Mov. Ecol., 5, doi:10.1186/s40462-017-0103-3, 2017.

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10 May 2017

Continuous time movement models resolve many of the problems with scaling, sampling, and interpretation that affect discrete movement models. They can, however, be challenging to estimate, have been presented in inconsistent ways, and are not widely used. We review the literature on integrated Ornstein-Uhlenbeck velocity models and propose four fundamental correlated velocity movement models (CVMâ€™s): random, advective, rotational, and rotational-advective. The models are defined in terms of biologically meaningful speeds and time scales of autocorrelation. We summarize several approaches to estimating the models, and apply these tools for the higher order task of behavioral partitioning via change point analysis. An array of simulation illustrate the precision and accuracy of the estimation tools. An analysis of a swimming track of a bowhead whale (Balaena mysticetus) illustrates their robustness to irregular and sparse sampling and identifies switches between slower and faster, and directed vs. random movements. An analysis of a short flight of a lesser kestrel (Falco naumanni) identifies exact moments when switches occur between loopy, thermal soaring and directed flapping or gliding flights. We provide tools to estimate parameters and perform change point analyses in continuous time movement models as an R package (smoove). These resources, together with the synthesis, should facilitate the wider application and development of correlated velocity models among movement ecologists.

Performance and retention of lightweight satellite radio tags applied to the ears of polar bears (Ursus maritimus)

Wiig, O., and 10 others including K.L. Laidre and E. Regehr, "Performance and retention of lightweight satellite radio tags applied to the ears of polar bears (Ursus maritimus)," Anim. Biotelem., 5, doi:10.1186/s40317-017-0124-0, 2017.

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13 Apr 2017

Satellite telemetry studies provide information that is critical to the conservation and management of species affected by ecological change. Here we report on the performance and retention of two types (SPOT-227 and SPOT-305A) of ear-mounted Argos-linked satellite transmitters (i.e., platform transmitter terminal, or PTT) deployed on free-ranging polar bears in Eastern Greenland, Baffin Bay, Kane Basin, the southern Beaufort Sea, and the Chukchi Sea during 2007–2013.

Transmissions from 142 out of 145 PTTs deployed on polar bears were received for an average of 69.3 days. The average functional longevity, defined as the number of days they transmitted while still attached to polar bears, for SPOT-227 was 56.8 days and for SPOT-305A was 48.6 days. Thirty-four of the 142 (24%) PTTs showed signs of being detached before they stopped transmitting, indicating that tag loss was an important aspect of tag failure. Furthermore, 10 of 26 (38%) bears that were re-observed following application of a PTT had a split ear pinna, suggesting that some transmitters were detached by force. All six PTTs that were still on bears upon recapture had lost the antenna, which indicates that antenna breakage was a significant contributor to PTT failure. Finally, only nine of the 142 (6%) PTTs—three of which were still attached to bears—had a final voltage reading close to the value indicating battery exhaustion. This suggests that battery exhaustion was not a major factor in tag performance.

The average functional longevity of approximately 2 months for ear-mounted PTTs (this study) is poor compared to PTT collars fitted to adult female polar bears, which can last for several years. Early failure of the ear-mounted PTTs appeared to be caused primarily by detachment from the ear or antenna breakage. We suggest that much smaller and lighter ear-mounted transmitters are necessary to reduce the risk of tissue irritation, tissue damage, and tag detachment, and with a more robust antenna design. Our results are applicable to other tag types (e.g., iridium and VHF systems) and to research on other large mammals that cannot wear radio collars.

Habitat selection by two beluga whale populations in the Chukchi and Beaufort seas

Hauser, D.D.W., K.L. Laidre, H.L. Stern, S.E. Moore, R.S. Suydam, and P.R. Richard, "Habitat selection by two beluga whale populations in the Chukchi and Beaufort seas," Plos One, 12, doi:10.1371/journal.pone.0172755, 2017.

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24 Feb 2017

There has been extensive sea ice loss in the Chukchi and Beaufort seas where two beluga whale (Delphinapterus leucas) populations occur between July–November. Our goal was to develop population-specific beluga habitat selection models that quantify relative use of sea ice and bathymetric features related to oceanographic processes, which can provide context to the importance of changing sea ice conditions. We established habitat selection models that incorporated daily sea ice measures (sea ice concentration, proximity to ice edge and dense ice) and bathymetric features (slope, depth, proximity to the continental slope, Barrow Canyon, and shore) to establish quantitative estimates of habitat use for the Eastern Chukchi Sea ('Chukchi') and Eastern Beaufort Sea ('Beaufort') populations. We applied 'used v. available' resource selection functions to locations of 65 whales tagged from 1993–2012, revealing large variations in seasonal habitat selection that were distinct between sex and population groups. Chukchi whales of both sexes were predicted to use areas in close proximity to Barrow Canyon (typically <200 km) as well as the continental slope in summer, although deeper water and denser ice were stronger predictors for males than females. Habitat selection differed more between sexes for Beaufort belugas. Beaufort males selected higher ice concentrations (≥40%) than females (0–40%) in July–August. Proximity to shore (<200 km) strongly predicted summer habitat of Beaufort females, while distance to the ice edge was important for male habitat selection, especially during westward migration in September. Overall, our results indicate that sea ice variables were rarely the primary drivers of beluga summer-fall habitat selection. While diminished sea ice may indirectly affect belugas through changes in the ecosystem, associations with bathymetric features that affect prey availability seemed key to habitat selection during summer and fall. These results provide a benchmark by which to assess future changes in beluga habitat use of the Pacific Arctic.

Advection in polar and sub-polar environments: Impacts on high latitude marine ecosystems

Hunt, G.L., and 17 others, including K. Laidre, "Advection in polar and sub-polar environments: Impacts on high latitude marine ecosystems," Prog. Oceanogr., 149, 40-81, doi:10.1016/j.pocean.2016.10.004, 2016.

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1 Dec 2016

Highlights

â€¢ Advection connects the Arctic with lower latitudes but isolates the Southern Ocean.
â€¢ Northward flowing waters have impact on Arctic productivity at all trophic levels.
â€¢ Arctic and Antarctic benthos, zooplankton and fish have contrasting evolutionary histories.
â€¢ Subpolar and polar fish, seabirds and marine mammals depend on advection of zooplankton.
â€¢ Climate change will affect polar marine ecosystem structure, function and connectivity.

Highly directional sonar beam of narwhals (Monodon monoceros) measured with a vertical 16 hydrophone array

Koblitz, J.C., P. Stilz, M.H. Rasmussen, and K.L. Laidre, "Highly directional sonar beam of narwhals (Monodon monoceros) measured with a vertical 16 hydrophone array," Plos One, 11, e0162069, doi:10.1371/journal.pone.0162069, 2016.

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9 Nov 2016

Recordings of narwhal (Monodon monoceros) echolocation signals were made using a linear 16 hydrophone array in the pack ice of Baffin Bay, West Greenland in 2013 at eleven sites. An average –3 dB beam width of 5.0° makes the narwhal click the most directional biosonar signal reported for any species to date. The beam shows a dorsal-ventral asymmetry with a narrower beam above the beam axis. This may be an evolutionary advantage for toothed whales to reduce echoes from the water surface or sea ice surface. Source level measurements show narwhal click intensities of up to 222 dB pp re 1 Î¼Pa, with a mean apparent source level of 215 dB pp re 1 Î¼Pa. During ascents and descents the narwhals perform scanning in the vertical plane with their sonar beam. This study provides valuable information for reference sonar parameters of narwhals and for the use of acoustic monitoring in the Arctic.

Use of glacial fronts by narwhals (Monodon monoceros) in West Greenland

Laidre, K.L., T. Moon, D.D.W. Hauser, R. McGovern, M.P. Heide-Jørgensen, R. Dietz, and B. Hudson, "Use of glacial fronts by narwhals (Monodon monoceros) in West Greenland," Proc. R. Soc. Biol. Lett., 12, doi:10.1098/rsbl.2016.0457, 2016.

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26 Oct 2016

Glacial fronts are important summer habitat for narwhals (Monodon monoceros); however, no studies have quantified which glacial properties attract whales. We investigated the importance of glacial habitats using telemetry data from n = 15 whales tagged in September of 1993, 1994, 2006 and 2007 in Melville Bay, West Greenland. For 41 marine-terminating glaciers, we estimated (i) narwhal presence/absence, (ii) number of 24 h periods spent at glaciers and (iii) the fraction of narwhals that visited each glacier (at 5, 7 and 10 km) in autumn. We also compiled data on glacier width, ice thickness, ice velocity, front advance/retreat, area and extent of iceberg discharge, bathymetry, subglacial freshwater run-off and sediment flux. Narwhal use of glacial habitats expanded in the 2000s probably due to reduced summer fast ice and later autumn freeze-up. Using a generalized multivariate framework, glacier ice front thickness (vertical height in the water column) was a significant covariate in all models. A negative relationship with glacier velocity was included in several models and glacier front width was a significant predictor in the 2000s. Results suggest narwhals prefer glaciers with potential for higher ambient freshwater melt over glaciers with silt-laden discharge. This may represent a preference for summer freshwater habitat, similar to other Arctic monodontids.

Sea-ice indicators of polar bear habitat

Stern, H.L., and K.L. Laidre, "Sea-ice indicators of polar bear habitat," Cyrosphere, 10, 2027-2041, doi:10.5194/tc-10-2027-2016, 2016.

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14 Sep 2016

Nineteen subpopulations of polar bears (Ursus maritimus) are found throughout the circumpolar Arctic, and in all regions they depend on sea ice as a platform for traveling, hunting, and breeding. Therefore polar bear phenology — the cycle of biological events — is linked to the timing of sea-ice retreat in spring and advance in fall. We analyzed the dates of sea-ice retreat and advance in all 19 polar bear subpopulation regions from 1979 to 2014, using daily sea-ice concentration data from satellite passive microwave instruments. We define the dates of sea-ice retreat and advance in a region as the dates when the area of sea ice drops below a certain threshold (retreat) on its way to the summer minimum or rises above the threshold (advance) on its way to the winter maximum. The threshold is chosen to be halfway between the historical (1979–2014) mean September and mean March sea-ice areas.

In all 19 regions there is a trend toward earlier sea-ice retreat and later sea-ice advance. Trends generally range from –3 to –9â€¯daysâ€¯decade^-1 in spring and from +3 to +9â€¯daysâ€¯decade^-1 in fall, with larger trends in the Barents Sea and central Arctic Basin. The trends are not sensitive to the threshold. We also calculated the number of days per year that the sea-ice area exceeded the threshold (termed ice-covered days) and the average sea-ice concentration from 1 June through 31 October. The number of ice-covered days is declining in all regions at the rate of –7 to –19â€¯daysâ€¯decade^-1, with larger trends in the Barents Sea and central Arctic Basin. The June–October sea-ice concentration is declining in all regions at rates ranging from –1 to –9â€¯percentâ€¯decade^-1. These sea-ice metrics (or indicators of habitat change) were designed to be useful for management agencies and for comparative purposes among subpopulations. We recommend that the National Climate Assessment include the timing of sea-ice retreat and advance in future reports.

High genetic variability of vagrant polar bears illustrates importance of population connectivity in fragmented sea ice habitats

Kutschera, V.E., and 12 others, including K.L. Laidre, "High genetic variability of vagrant polar bears illustrates importance of population connectivity in fragmented sea ice habitats," Anim. Conserv., 19, 337-349, doi:10.1111/acv.12250, 2016.

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1 Aug 2016

Projections by the Intergovernmental Panel on Climate Change (IPCC) and sea ice forecasts suggest that Arctic sea ice will decline markedly in coming decades. Expected effects on the entire ecosystem include a contraction of suitable polar bear habitat into one or few refugia. Such large-scale habitat decline and fragmentation could lead to reduced genetic diversity. Here we compare genetic variability of four vagrant polar bears that reached Iceland with that in recognized subpopulations from across the range, examining 23 autosomal microsatellites, mitochondrial control region sequences and Y-chromosomal markers. The vagrants' genotypes grouped with different genetic clusters and showed similar genetic variability at autosomal microsatellites (expected heterozygosity, allelic richness, and individual heterozygosity) as individuals in recognized subpopulations. Each vagrant carried a different mitochondrial haplotype. A likely route for polar bears to reach Iceland is via Fram Strait, a major gateway for the physical exportation of sea ice from the Arctic basin. Vagrant polar bears on Iceland likely originated from more than one recognized subpopulation, and may have been caught in sea ice export during long-distance movements to the East Greenland area. Although their potentially diverse geographic origins might suggest that these vagrants encompass much higher genetic variability than vagrants or dispersers in other regions, the four Icelandic vagrants encompassed similar genetic variability as any four randomly picked individuals from a single subpopulation or from the entire sample. We suggest that this is a consequence of the low overall genetic variability and weak range-wide genetic structuring of polar bears — few dispersers can represent a large portion of the species' gene pool. As predicted by theory and our demographic simulations, continued gene flow will be necessary to counteract loss of genetic variability in increasingly fragmented Arctic habitats. Similar considerations will be important in the management of other taxa that utilize sea ice habitats.

High genetic variability of vagrant polar bears illustrates importance of population connectivity in fragmented sea ice habitats

Kutschera, V.E., and 12 others, including K.L. Laidre, "High genetic variability of vagrant polar bears illustrates importance of population connectivity in fragmented sea ice habitats," Animal Conserv., 19, 337-349, doi:10.1111/acv.12250, 2016.

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7 Jan 2016

Projections by the Intergovernmental Panel on Climate Change (IPCC) and sea ice forecasts suggest that Arctic sea ice will decline markedly in coming decades. Expected effects on the entire ecosystem include a contraction of suitable polar bear habitat into one or few refugia. Such large-scale habitat decline and fragmentation could lead to reduced genetic diversity. Here we compare genetic variability of four vagrant polar bears that reached Iceland with that in recognized subpopulations from across the range, examining 23 autosomal microsatellites, mitochondrial control region sequences and Y-chromosomal markers. The vagrants' genotypes grouped with different genetic clusters and showed similar genetic variability at autosomal microsatellites (expected heterozygosity, allelic richness, and individual heterozygosity) as individuals in recognized subpopulations. Each vagrant carried a different mitochondrial haplotype. A likely route for polar bears to reach Iceland is via Fram Strait, a major gateway for the physical exportation of sea ice from the Arctic basin. Vagrant polar bears on Iceland likely originated from more than one recognized subpopulation, and may have been caught in sea ice export during long-distance movements to the East Greenland area. Although their potentially diverse geographic origins might suggest that these vagrants encompass much higher genetic variability than vagrants or dispersers in other regions, the four Icelandic vagrants encompassed similar genetic variability as any four randomly picked individuals from a single subpopulation or from the entire sample. We suggest that this is a consequence of the low overall genetic variability and weak range-wide genetic structuring of polar bears — few dispersers can represent a large portion of the species' gene pool. As predicted by theory and our demographic simulations, continued gene flow will be necessary to counteract loss of genetic variability in increasingly fragmented Arctic habitats. Similar considerations will be important in the management of other taxa that utilize sea ice habitats.

Regional diving behavior of Pacific Arctic beluga whales Delphinapterus leucas and possible associations with prey

Hauser, D.D.W., K.L. Laidre, S.L. Parker-Stetter, J.K. Horne, R.S. Suydam, and P.R. Richard, "Regional diving behavior of Pacific Arctic beluga whales Delphinapterus leucas and possible associations with prey," Mar. Ecol. Prog. Ser., 541, 245-264, doi:10.3354/meps11530, 2015.

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15 Dec 2015

Two populations of beluga whales Delphinapterus leucas in the Pacific Arctic make seasonal migrations to regions characterized by diverse bathymetry and hydrography, yet there is limited information contrasting behavior and foraging across regions. We used satellite-linked time-depth recorders attached to 30 belugas from 1997 to 2012 to infer the depths at which belugas forage seasonally and regionally. We also examined the correspondence between patterns of beluga diving and the vertical distribution of a primary prey species, Arctic cod Boreogadus saida, within the western Beaufort Sea. A suite of regional diving metrics revealed that beluga dive behavior varied among regions and sometimes between populations. Estimates of occupancy time at depth, in addition to maximum and modal dive depths for 6 h periods, suggested that Eastern Chukchi Sea and Beaufort Sea belugas were regularly diving to the seafloor in shallow shelf regions. Along slope margins and in the deep Canada Basin (>3000 m), specific portions of the water column were more frequently targeted. The greatest maximum daily dive depths were >900 m in the Canada Basin. Arctic cod were most abundant at 200–300 m in the western Beaufort Sea, and beluga dives within the survey area also most frequently targeted these depths. These results are consistent with a hypothesis that Arctic cod are a primary prey item for Pacific Arctic belugas and suggest that foraging belugas dive to depths that maximize prey encounters. In the context of a rapidly transforming Arctic ecosystem increasingly exposed to anthropogenic activities, our results quantify the ecological importance of key regions for these 2 populations.

Bowhead whale body condition and links to summer sea ice and upwelling in the Beaufort Sea

George, J.C., M.L. Druckenmiller, K.L. Laidre, R. Suydam, and B. Person, "Bowhead whale body condition and links to summer sea ice and upwelling in the Beaufort Sea," Prog. Oceanogr., 136, 250-262, doi:10.1016/j.pocean.2015.05.001, 2015.

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1 Aug 2015

We examined the response of bowhead whale (Baleen mysticetus) body condition to summer sea ice conditions and upwelling-favorable winds. We used a long-term dataset collected from whales of the Bering-Chukchi-Beaufort Seas (BCB) stock to estimate various body condition indices (BCI's) for individual whales that were harvested by Alaskan Eskimos. A series of offshore regions frequented by bowhead whales in summer were delineated and used to quantify interannual summertime environmental conditions including: (a) mean open water fraction, (b) duration of melt season, (c) date of continuous freeze-up, and (d) mean upwelling-favorable wind stress. Body condition was analyzed relative to these metrics for both the preceding summer feeding season and the previous three seasons combined. Our analysis indicates a significant increase in the long-term trend in an axillary girth-based body condition index (BCI_G) over the study period (1989–2011). The increase in BCI_G is likely associated with the trend in overall reduction of sea ice, including increased duration of open water, changes in upwelling potential (wind stress), and possibly higher primary production in the Pacific Arctic marine ecosystem favoring water-column invertebrates. We found strong significant positive correlations between BCI_G and late summer open water fraction in the Beaufort Sea and smaller nearshore areas off the Mackenzie Delta and west of Banks Island. Additionally, BCI_G was positively and significantly correlated with duration of melt season, later date of freeze-up in the Beaufort Sea, and upwelling-favorable winds on the Mackenzie shelf and west of Banks Island. A strong seasonal difference in BCI%u2019s was noted for subadult bowheads, presumably associated with summer feeding; however, yearlings were found to drop in BCI over at least the first summer after weaning. Our results indicate an overall increase in bowhead whale body condition and a positive correlation with summer sea ice loss over the last 2.5 decades in the Pacific Arctic. We speculate that sea ice loss has positive effects on secondary trophic production within the BCB bowhead's summer feeding region. While not part of this study, the abundance of BCB bowheads increased markedly over the same period.

The relationship between sea ice concentration and the spatio-temporal distribution of vocalizing bearded seals (Erignathus barbatus) in the Bering, Chukchi, and Beaufort seas from 2008 to 2011

Macintyre, K.Q., K.M. Stafford, P.B. Conn, K.L. Laidre, and P.L. Boveng, "The relationship between sea ice concentration and the spatio-temporal distribution of vocalizing bearded seals (Erignathus barbatus) in the Bering, Chukchi, and Beaufort seas from 2008 to 2011," Prog. Oceanogr., 136, 241-249, doi:10.1016/j.pocean.2015.05.008, 2015.

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26 May 2015

Bearded seals (Erignathus barbatus) are widely distributed in the Arctic and sub-Arctic; the Beringia population is found throughout the Bering, Chukchi and Beaufort Seas (BCB). Bearded seals are highly vocal, using underwater calls to advertise their breeding condition and maintain aquatic territories. They are also closely associated with pack ice for reproductive activities, molting, and resting. Sea ice habitat for this species varies spatially and temporally throughout the year due to differences in underlying physical and oceanographic features across its range. To test the hypothesis that the vocal activity of bearded seals is related to variations in sea ice, passive acoustic data were collected from nine locations throughout the BCB from 2008 to 2011. Recording instruments sampled on varying duty cycles ranging from 20% to 100% of each hour, and recorded frequencies up to 8192 Hz. Spectrograms of acoustic data were analyzed manually to calculate the daily proportion of hours with bearded seal calls at each sampling location, and these call activity proportions were correlated with daily satellite-derived estimates of sea ice concentration. Bearded seals were vocally active nearly year-round in the Beaufort and Chukchi Seas with peak activity occurring from mid-March to late June during the mating season. The duration of call activity in the Bering Sea was shorter, lasting typically only five months, and peaked from mid-March to May at the northernmost recorders. In all areas, call activity was significantly correlated with higher sea ice concentrations (p < 0.01). These results suggest that losses in ice cover may negatively impact bearded seals, not just by loss of habitat but also by altering the behavioral ecology of the BCB population.

Arctic marine mammal population status, sea ice habitat loss, and conservation recommendations for the 21st century

Laidre, K.L., H. Stern, K.M. Kovacs, L. Lowry, S.E. Moore, E.V. Regehr, S.H. Ferguson, Ø. Wiig, P. Boveng, R.P. Angliss, E.W Born, D. Litovka, L. Quakenbush, C. Lydersen, D. Vongraven, and F. Ugarte, "Arctic marine mammal population status, sea ice habitat loss, and conservation recommendations for the 21st century," Conserv. Biol., 29, 724-737, doi:10.1111/cobi.12474, 2015.

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17 Mar 2015

Arctic marine mammals (AMMs) are icons of climate change, largely because of their close association with sea ice. However, neither a circumpolar assessment of AMM status nor a standardized metric of sea ice habitat change is available. We summarized available data on abundance and trend for each AMM species and recognized subpopulation. We also examined species diversity, the extent of human use, and temporal trends in sea ice habitat for 12 regions of the Arctic by calculating the dates of spring sea ice retreat and fall sea ice advance from satellite data (1979–2013). Estimates of AMM abundance varied greatly in quality, and few studies were long enough for trend analysis. Of the AMM subpopulations, 78% (61 of 78) are legally harvested for subsistence purposes. Changes in sea ice phenology have been profound. In all regions except the Bering Sea, the duration of the summer (i.e., reduced ice) period increased by 5–10 weeks and by >20 weeks in the Barents Sea between 1979 and 2013. In light of generally poor data, the importance of human use, and forecasted environmental changes in the 21st century, we recommend the following for effective AMM conservation: maintain and improve comanagement by local, federal, and international partners; recognize spatial and temporal variability in AMM subpopulation response to climate change; implement monitoring programs with clear goals; mitigate cumulative impacts of increased human activity; and recognize the limits of current protected species legislation.

Shifts in female polar bear (Ursus maritimus) habitat use in East Greenland

Laidre, K.L., E.W. Born, P. Heagerty, Ø. Wiig, H. Stern, R. Dietz, J. Aars, and M. Andersen, "Shifts in female polar bear (Ursus maritimus) habitat use in East Greenland," Polar Biol., 38, 879-893, doi:10.1007/s00300-015-1648-5, 2015.

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6 Feb 2015

Few studies have investigated the impacts of climate change on polar bears (Ursus maritimus) in East Greenland (EG), where some of the largest rates of sea ice loss have occurred. We used remotely sensed sea ice data to quantify changes in timing of sea ice freeze-up and breakup in EG polar bear habitat between 1979 and 2012. We then quantified movement rates, area use, habitat selection, and distribution and phenology of maternity denning using data from adult female polar bears tracked with satellite transmitters between 2007 and 2010 (n = 7). We compared results to historical data collected from adult females in the 1990s (n = 4). Adult females in the 2000s used areas with significantly lower sea ice concentrations (10–15% lower) than bears in the 1990s during winter, a pattern influenced by delayed freeze-up in October–December. Adult females in the 2000s were located significantly closer (100–150 km) to open water in all seasons and spent approximately 2 months longer in areas with <60% sea ice concentration than bears in the 1990s. Multivariate resource selection models contrasting preference between decades showed that there was a statistically significant and stronger winter preference in the 2000s for adult females to select for higher sea ice concentrations. Timing of maternity denning did not significantly differ between decades. Results indicate that multi-decadal loss of sea ice has resulted in shifts in polar bear habitat use in EG.

Trends in bowhead whales in West Greenland: Aerial surveys vs. genetic capture-recapture analyses

Rekdal, S.L., and 9 others including K.L. Laidre, "Trends in bowhead whales in West Greenland: Aerial surveys vs. genetic capture-recapture analyses," Mar. Mammal Sci., 31, 133-154, doi:10.1111/mms.12150, 2015.

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1 Jan 2015

We contrast two methods for estimating the trends of bowhead whales (Balaena mysticetus) in West Greenland: (1) double platform visual aerial survey, corrected for missed sightings and the time the whales are available at the surface; and (2) a genetic capture-recapture approach based on a 14-yr-long biopsy sampling program in Disko Bay. The aerial survey covered 39,000 km² and resulted in 58 sightings, yielding an abundance estimate of 744 whales (CV = 0.34, 95% CI: 357–1,461). The genetic method relied on determining sex, mitochondrial haplotypes and genotypes of nine microsatellite markers. Based on samples from a total of 427 individuals, with 11 recaptures from previous years in 2013, this resulted in an estimate of 1,538 whales (CV = 0.24, 95% CI: 827–2,249). While the aerial survey is considered a snapshot of the local spring aggregation in Disko Bay, the genetic approach estimates the abundance of the source of this aggregation. As the whales in Disko Bay primarily are adult females that do not visit the bay annually, the genetic method would presumably yield higher estimates. The studies indicate that an increase in abundance observed between 1998 and 2006 has leveled off.

Seasonal variability of the warm Atlantic water layer in the vicinity of the Greenland shelf break

Grist, J.P., et al. including K.L. Laidre, "Seasonal variability of the warm Atlantic water layer in the vicinity of the Greenland shelf break," Geophys. Res. Lett., 41, 8530-8537, doi:10.1002/2014GL062051, 2014.

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16 Dec 2014

The warmest water reaching the east and west coast of Greenland is found between 200 and 600%u2009m. While important for melting Greenland's outlet glaciers, limited winter observations of this layer prohibit determination of its seasonality. To address this, temperature data from Argo profiling floats, a range of sources within the World Ocean Database, and unprecedented coverage from marine-mammal borne sensors have been analyzed for the period 2002%u20132011. A significant seasonal range in temperature (~1–2°C) is found in the warm layer, in contrast to most of the surrounding ocean. The phase of the seasonal cycle exhibits considerable spatial variability, with the warmest water found near the eastern and southwestern shelf break toward the end of the calendar year. High-resolution ocean model trajectory analysis suggests the timing of the arrival of the year's warmest water is a function of advection time from the subduction site in the Irminger Basin.

Population-specific home ranges and migration timing of Pacific Arctic beluga whales (Delphinapterus leucas)

Hauser, D.D.W., K.L. Laidre, R.S. Suydam, and P.R. Richard, "Population-specific home ranges and migration timing of Pacific Arctic beluga whales (Delphinapterus leucas)," Polar Biol., 8, 1171-1183, doi:10.1007/s00300-014-1510-1, 2014.

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1 Apr 2014

Two populations of beluga whales (Delphinapterus leucas), the Eastern Beaufort Sea (BS) and Eastern Chukchi Sea (ECS), make extensive seasonal migrations into the Pacific Arctic. However, the extent to which these populations overlap in time and space is not known. We quantified distribution and migration patterns for BS and ECS belugas using daily locations from whales tracked with satellite-linked transmitters. Home ranges and core areas in summer (July and August) and in each month (July–November), daily displacement, dispersal from core areas, and autumn migration timing were estimated. Distinct summer and fall distribution patterns and staggered autumn migration timing were identified for BS and ECS whales. Summer home ranges for each population had less than 10% overlap. Monthly home ranges were also relatively distinct between populations except in September (up to 88% home range overlap). A distinct east–west shift in focal area use occurred in September that persisted into October, with the two populations essentially switching longitudinal positions. Highest daily displacements occurred during the migratory period in September for BS whales and October for ECS whales, further indicating westward fall migration was offset between populations. Sexual segregation of males and females within a population also varied monthly. Autumn migration timing as well as differences in spatial and temporal segregation between BS and ECS beluga populations may be a result of maternally driven philopatry and population-specific adaptations to dynamically available resources. Our results contribute to the management of these populations by identifying seasonal area use and differences in migration patterns.

Modeling climate change impacts on phenology and population dynamics of migratory marine species

Anderson, J.J., E. Gurarie, C. Bracis, B.J. Burke, and K.L. Laidre, "Modeling climate change impacts on phenology and population dynamics of migratory marine species," Ecol. Model., 264, 83-97, doi:10.1016/j.ecolmodel.2013.03.009, 2013.

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24 Aug 2013

We review literature concerning the impacts of climate change on the migration of marine species, with an emphasis on the adaptation of migration phenology through genetic tracking and phenotypic plasticity. We then develop an individual-based modeling framework characterizing the effects of climate change on phenology and population dynamics. In the framework, an animal's ability to match its environmental preferences, its bioclimate envelope, to the environmental conditions by adjusting its migration timing between foraging and breeding habitats determines its condition, survival, and fecundity. Climate-induced changes in the envelope produce timing mismatches that result in a population adapting its phenology through both genetic and plastic processes. Model results suggest: (1) the temporal size of the bioclimate envelope is an important determinant of a population's sensitivity to climate change and susceptibility to extinction, (2) population extinction can occur if the rate of change in the timing of the envelope exceeds the rate its phenology changes or if the variability in the envelope exceeds the population's inherent capacity for variability, (3) a population with migration timing cued by photoperiod is expected to exhibit weaker phenotypic plasticity than one cued by temperature, and (4) population extinction in response to climate change follows a threshold pattern such that population size may not be a reliable indicator of extinction threat, although variability in average individual condition across years may be an extinction threat indicator. Finally, while the model is intentionally simplistic, we discuss how it can be extended to cover more complex interactions.

A metapopulation model for Canadian and West Greenland narwhals

Heide-Jørgensen, M.P., P.R. Richard, R. Dietz, and K.L. Laidre, "A metapopulation model for Canadian and West Greenland narwhals," Anim. Conserv., 16, 331-343, doi:10.1111/acv.12000, 2013.

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1 Jun 2013

A model of the metapopulation structure of narwhals Monodon monoceros in Baffin Bay, Hudson Bay and adjacent waters is proposed based on satellite telemetry data collected over two decades from six coastal aggregations of narwhals in the eastern Canadian high Arctic, Hudson Bay and West Greenland. In addition, data on seasonal catches of narwhals in 11 Inuit communities are used to provide information on the occurrence of narwhals. The tracking data suggest that disjunct summer aggregations of narwhals are, to some extent, demographically independent subpopulations, with minimal or no exchange with other summering aggregations. We propose that these should be considered separate stocks for management purposes. Year-round satellite tracking of individuals demonstrates that whales return to the same summering areas the following year, suggesting inter-annual site fidelity. We propose that the narwhals in Canada constitute five separate stocks, with limited exchange between three of the stocks. Coastal summer aggregations in Greenland constitute two stocks in addition to two fall and winter aggregations supplied by narwhals from several summering areas. Several narwhal stocks mix on the wintering areas in Baffin Bay, but the metapopulation structure is likely maintained through a combination of life-history traits and migratory routes, as mating most likely occurs after the initiation of the return migration toward summering areas. The metapopulation structure in Baffin Bay narwhals will be impacted differentially by Inuit subsistence hunting, depending on the migratory schedule of narwhals and dates at which whales occur in different seasonal hunting areas. It is therefore important to identify which narwhal stocks contribute to which subsistence hunts in order to assess the sustainability of those hunts. This paper proposes a preliminary stock model for this purpose.

Females roam while males patrol: Comparing movements of adult male and adult female polar bears during the springtime breeding season

Laidre, K.L., E.W. Born, E. Gurarie, Ø. Wiig, R. Dietz, and H. Stern, "Females roam while males patrol: Comparing movements of adult male and adult female polar bears during the springtime breeding season," Proc. R. Soc. B, 280, doi:10.1098/rspb.2012.2371, 2013.

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1 Feb 2013

Intraspecific differences in movement behaviour reflect different tactics used by individuals or sexes to favour strategies that maximize fitness. We report movement data collected from n = 23 adult male polar bears with novel ear-attached transmitters in two separate pack ice subpopulations over five breeding seasons. We compared movements with n = 26 concurrently tagged adult females, and analysed velocities, movement tortuosity, range sizes and habitat selection with respect to sex, reproductive status and body mass. There were no differences in 4-day displacements or sea ice habitat selection for sex or population. By contrast, adult females in all years and both populations had significantly more linear movements and significantly larger breeding range sizes than males. We hypothesized that differences were related to encounter rates, and used observed movement metrics to parametrize a simulation model of male–male and male–female encounter. The simulation showed that the more tortuous movement of males leads to significantly longer times to male–male encounter, while having little impact on male–female encounter. By contrast, linear movements of females are consistent with a prioritized search for sparsely distributed prey. These results suggest a possible mechanism for explaining the smaller breeding range sizes of some solitary male carnivores compared to females.

Marine mammals

Laidre, K.L., "Marine mammals," In Arctic Report Card, M.O. Jeffries, J.A. Richter-Menge, and J.E. Overland, eds., 77-81 (NOAA Climate Program Office, 2012).

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5 Dec 2012

Highlights

Species richness for core Arctic marine mammals is highest in three regions: Baffin Bay, Davis Strait and the Barents Sea, where nine of eleven species are present. Most other regions have seven or eight core species, while the Beaufort Sea and the Sea of Okhotsk regions have only six species.

Two acoustic recorders in Fram Strait during the International Polar Year (2007-2009) documented critically endangered Spitzbergen bowhead whales singing almost continuously through the winter.

In Hudson Bay, later departures of beluga from their summering grounds have been linked to warmer and more spatially more heterogeneous sea temperatures.

The utility of harvest recoveries of marked individuals to assess polar bear (Ursus maritimus) survival

Peacock, E., J. Laake, K.L. Laidre, E.W. Born, and S.N. Atkinson, "The utility of harvest recoveries of marked individuals to assess polar bear (Ursus maritimus) survival," Arctic, 65, 391-400, 2012.

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1 Dec 2012

Management of polar bear (Ursus maritimus) populations requires the periodic assessment of life history metrics such as survival rate. This information is frequently obtained during short-term capture and marking efforts (e.g., over the course of three years) that result in hundreds of marked bears remaining in the population after active marking is finished. Using 10 additional years of harvest recovery subsequent to a period of active marking, we provide updated estimates of annual survival for polar bears in the Baffin Bay population of Greenland and Canada. Our analysis suggests a decline in survival of polar bears since the period of active marking that ended in 1997; some of the decline in survival can likely be attributed to a decline in springtime ice concentration over the continental shelf of Baffin Island. The variance around the survival estimates is comparatively high because of the declining number of marks available; therefore, results must be interpreted with caution. The variance of the estimates of survival increased most substantially in the sixth year post-marking. When survival estimates calculated with recovery-only and recapture-recovery data sets from the period of active marking were compared, survival rates were indistinguishable. However, for the period when fewer marks were available, survival estimates were lower using the recovery-only data set, which indicates that part of the decline we detected for 2003 %u2013 09 may be due to using only harvest recovery data. Nevertheless, the decline in the estimates of survival is consistent with population projections derived from harvest numbers and earlier vital rates, as well as with an observed decline in the extent of sea ice habitat.

A metapopulation model for Canadian and West Greenland narwhals

Heide-Jørgensen, M.P., P.R. Richard, R. Dietz, and K.L. Laidre, "A metapopulation model for Canadian and West Greenland narwhals," Anim. Conserv., EOR, doi:10.1111/acv.12000, 2012.

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13 Nov 2012

A model of the metapopulation structure of narwhals Monodon monoceros in Baffin Bay, Hudson Bay and adjacent waters is proposed based on satellite telemetry data collected over two decades from six coastal aggregations of narwhals in the eastern Canadian high Arctic, Hudson Bay and West Greenland. In addition, data on seasonal catches of narwhals in 11 Inuit communities are used to provide information on the occurrence of narwhals. The tracking data suggest that disjunct summer aggregations of narwhals are, to some extent, demographically independent subpopulations, with minimal or no exchange with other summering aggregations. We propose that these should be considered separate stocks for management purposes. Year-round satellite tracking of individuals demonstrates that whales return to the same summering areas the following year, suggesting inter-annual site fidelity. We propose that the narwhals in Canada constitute five separate stocks, with limited exchange between three of the stocks. Coastal summer aggregations in Greenland constitute two stocks in addition to two fall and winter aggregations supplied by narwhals from several summering areas. Several narwhal stocks mix on the wintering areas in Baffin Bay, but the metapopulation structure is likely maintained through a combination of life-history traits and migratory routes, as mating most likely occurs after the initiation of the return migration toward summering areas. The metapopulation structure in Baffin Bay narwhals will be impacted differentially by Inuit subsistence hunting, depending on the migratory schedule of narwhals and dates at which whales occur in different seasonal hunting areas. It is therefore important to identify which narwhal stocks contribute to which subsistence hunts in order to assess the sustainability of those hunts. This paper proposes a preliminary stock model for this purpose.

Do trophic cascades affect the storage and flux of atmospheric carbon? An analysis of sea otters and kelp forests

Wilmers, C.C., J.A. Estes, M. Edwards, K.L. Laidre, and B. Konar, "Do trophic cascades affect the storage and flux of atmospheric carbon? An analysis of sea otters and kelp forests," Frontier Ecol. Environ., 10, 409-415, doi:10.1890/110176, 2012.

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1 Oct 2012

We combine data collected from the past 40 years to estimate the indirect effects of sea otters (Enhydra lutris) on ecosystem carbon (C) production and storage across their North American range, from Vancouver Island to the western edge of Alaska's Aleutian Islands. We find that sea otters, by suppressing sea urchin (Strongylocentrotus spp) populations, allow kelp (Order Laminariales) ecosystems to develop with a net primary productivity (NPP) of 313%u2013900 grams C per square meter per year (g C m^-2 yr^-1) and biomass density of 101–180 grams C per square meter (g C m^-2). In the absence of sea otters, these areas would have an NPP of 25–70 g C m^-2 yr^-1 and biomass density of 8–14 g C m^-2. Over an ecosystem area of approximately 5.1 x 10¹⁰ m², the effect of sea otter predation on living kelp biomass alone represents a 4.4-to 8.7-teragram increase in C storage. At 2012 prices (US$47 per ton of C), this stored C would be valued at US$205 million–$408 million on the European Carbon Exchange. Although questions remain concerning the pathways and compartments of kelp C flux and storage, sea otters undoubtedly have a strong influence on these elements of the C cycle. Predator-induced trophic cascades likely influence the rates of C flux and storage in many other species and ecosystems.

Identifying gray whale (Eschrichtius robustus) foraging grounds along the Chukotka Peninsula, Russia, using satellite telemetry

Heide-Jørgensen, M.P., K.L. Laidre, D. Litovka, M. Villum Jensen, J.M. Grebmeier, and B.I. Sirenko, "Identifying gray whale (Eschrichtius robustus) foraging grounds along the Chukotka Peninsula, Russia, using satellite telemetry," Polar Biol., 35, 1035-1045, doi: 10.1007/s00300-011-1151-6, 2012.

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1 Jul 2012

The purpose of this study was to evaluate summer and fall residency and habitat selection by gray whales, Eschrichtius robustus, together with the biomass of benthic amphipod prey on the coastal feeding grounds along the Chukotka Peninsula. Thirteen gray whales were instrumented with satellite transmitters in September 2006 near the Chukotka Peninsula, Russia. Nine transmitters provided positions from whales for up to 81 days. The whales travelled within 5 km of the Chukotka coast for most of the period they were tracked with only occasional movements offshore. The average daily travel speeds were 23 km day^-1 (range 9–53 km day^-1). Four of the whales had daily average travel speeds <1 km day^-1 suggesting strong fidelity to the study area. The area containing 95% of the locations for individual whales during biweekly periods was on average 13,027 km² (range 7,097–15,896 km²). More than 65% of all locations were in water <30 m, and between 45 and 70% of biweekly kernel home ranges were located in depths between 31 and 50 m. Benthic density of amphipods within the Bering Strait at depths <50 m was on average ~54 g wet wt m² in 2006. It is likely that the abundant benthic biomass is more than sufficient forage to support the current gray whale population. The use of satellite telemetry in this study quantifies space use and movement patterns of gray whales along the Chukotka coast and identifies key feeding areas.

Spring partitioning of Disko Bay, West Greenland, by arctic and subarctic baleen whales

Laidre, K.L., and M.P. Heide-Jørgensen, "Spring partitioning of Disko Bay, West Greenland, by arctic and subarctic baleen whales," ICES J. Mar. Sci., 69, doi:10.1093/icesjms/fss095, 2012.

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24 May 2012

Movements of co-occurring bowhead (Balaena mysticetus) and humpback (Megaptera novaeangliae) whales in Disko Bay, West Greenland, were examined using satellite telemetry. Data on movements, habitat use, and phenology were collected from tagged 49 bowheads and 44 humpbacks during the transition from sea-ice breakup to open water between 2008 and 2010. Bowhead whales began their northward spring migration around 27 May (median day-of-the-year departure date = 147, interquartile range 141–153) and were distributed broadly in northern and central Disko Bay in water depths between 100 and 400 m. Humpback whales arrived in Disko Bay no later than 2 June and were located in shallow water (<100 m) along the coasts of the mainland or Disko Island. Trends in departure date from Disko Bay were significant for bowhead whales (~15 d later, p < 0.001) between two periods: 2001–2006 and 2008–2010. Many species are predicted to arrive earlier in the Arctic and to expand their range northwards with reduced sea ice and increasing temperatures under climate change. Quantifying the spatial and temporal relationships between co-occurring Arctic and Subarctic top predators allows for baseline insight to be gained on how climate change might alter interspecies interactions.

The Northwest Passage opens for bowhead whales

Heide-Jorgensen, M.P., K.L. Laidre, L.T. Quakenbush, and J.J. Citta, "The Northwest Passage opens for bowhead whales," Biol. Lett., 8, 270-273, doi:10.1098/rsbl.2011.0731, 2011.

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23 Apr 2012

The loss of Arctic sea ice is predicted to open up the Northwest Passage, shortening shipping routes and facilitating the exchange of marine organisms between the Atlantic and the Pacific oceans. Here, we present the first observations of distribution overlap of bowhead whales (Balaena mysticetus) from the two oceans in the Northwest Passage, demonstrating this route is already connecting whales from two populations that have been assumed to be separated by sea ice. Previous satellite tracking has demonstrated that bowhead whales from West Greenland and Alaska enter the ice-infested channels of the Canadian High Arctic during summer. In August 2010, two bowhead whales from West Greenland and Alaska entered the Northwest Passage from opposite directions and spent approximately 10 days in the same area, documenting overlap between the two populations.

First acoustic recordings of narwhals (Monodon monoceros) in winter

Stafford, K.M., K.L. Laidre and M.P. Heide-Jørgensen, "First acoustic recordings of narwhals (Monodon monoceros) in winter," Mar. Mammal Sci., 28, E197-E207, doi:10.1111/j.1748-7692.2011.00500.x, 2012.

1 Apr 2012

Geographic variation in cranial morphology of narwhals (Monodon monoceros) from Greenland and the eastern Canadian Arctic

Wiig, O., M.P. Heide-Jorgensen, K.L. Laidre, E. Garde, and R.R. Reeves, "Geographic variation in cranial morphology of narwhals (Monodon monoceros) from Greenland and the eastern Canadian Arctic," Polar Biol., 35, 63-71, doi: 10.1007/s00300-011-1032-z, 2011.

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1 Jan 2012

We analyzed variation in nine non-metric and eight metric variables in the skulls of 132 narwhals (Monodon monoceros) from five localities in Greenland (Inglefield Bredning, Melville Bay, Uummannaq, Disko Bay, and Scoresby Sound) and one in the eastern Canadian Arctic (Eclipse Sound). Metric variables were used to compare the combined Disko Bay and Uummannaq samples with the samples from Inglefield Bredning and Scoresby Sound using three different multivariate techniques for each sex. None of the results were significant. Seven of the non-metric variables were independent of age and sex and were used in comparing samples from the six localities. No differences were found among the four localities in West Greenland, but differences were found in two of the non-metric variables between the combined West Greenland sample and the one from Scoresby Sound. A major shortcoming of the analysis based on metric data was the small sample size from several of the areas, which resulted in low statistical power. Genetic as well as environmental factors could explain the differences detected here between narwhals living along the west and the east coasts of Greenland.

Unusual narwhal sea ice entrapments and delayed autumn freeze-up trends

Laidre, K.L., M.P. Heide-Jørgensen, H. Stern, and P. Richard, "Unusual narwhal sea ice entrapments and delayed autumn freeze-up trends," Polar Biol., 35, 149-154, doi:10.1007/s00300-011-1036-8, 2012.

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1 Jan 2012

Sea ice entrapments of narwhals (Monodon monoceros) occur when rapid changes in weather and wind conditions create a formation of fast ice in bays or passages used by whales. Between 2008 and 2010, four entrapments of narwhals were reported in Canada and Greenland. In each case, large groups (40–600 individuals) succumbed in the sea ice at three separate summering localities, two of these where entrapments had never before been reported. We examined long-term trends in autumn freeze-up timing (date when sea ice concentration rises above some threshold) on the 6 largest narwhal summering areas using sea ice concentration from satellite passive microwave data (1979–2009). We found strongly positive and significant trends (P < 0.001) in progressively later dates of autumn freeze-up in all summering areas. Autumn freeze-up occurs between 0.5 and 1 day later per year, or roughly 2–4 weeks later, over the 31-year time series. This indicates that sea ice conditions on narwhal summering areas are changing rapidly. The question remains whether entrapment events on summering areas are random or whether narwhals are adapting to changes in sea ice freeze-up by prolonging their summer residence time.

Recaptures of genotyped bowhead whales (Balaena mysticetus) in Eastern Canada and West Greenland

Wiig, O., M.P. Heide-Jorgensen, C. Lindquist, K.L. Laidre, L. Postma, L. Dueck, P. Palsboll, and L. Bachmann, "Recaptures of genotyped bowhead whales (Balaena mysticetus) in Eastern Canada and West Greenland," Endangered Species Res., 14, 235-242, doi:10.3354/esr00365, 2011.

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23 Sep 2011

Multi-locus genotype and sex were used to identify individual bowhead whales Balaena mysticetus from 710 samples collected between 1995 and 2010 at 4 localities in eastern Canada (Foxe Basin, Pelly Bay, Repulse Bay, and Cumberland Sound) and at 1 locality in West Greenland (Disko Bay). In total, 29 recaptures of the same individuals were identified between years, of which 26 individuals were recaptured within the same locality. The remaining 3 were recaptured between sampling localities, from 2 putative International Whaling Commission (IWC) stocks: the Hudson Bay-Foxe Basin stock and the Baffin Bay-Davis Strait stock. These recaptures agree with satellite tracking results that demonstrate movement between IWC stocks and question whether these stocks are true biological entities. The intervals between capture and recapture of females in Disko Bay ranged from 1 to 8 yr. The observed number of multi-year recaptures compared to the expected numbers of recaptures did not indicate any clear cyclicity in the use of Disko Bay consistent with the notion that the migration pattern of females to this area might be tied to their reproductive cycles. A mark-recapture estimate of whales identified in 2010 compared to all identifications between 2000 and 2009 resulted in an estimate of 1410 bowhead whales (SE = 320, 95% CI: 783-2038) constituting the spring aggregation in Disko Bay. The estimate for the female portion of the aggregation was 999 individuals (SE = 231, 95% CI: 546-1452). The multi-year cycle of appearance in Disko Bay emphasizes the necessity for identifying whales over multiple years for inclusion in mark-recapture estimation.

Life in the lead: extreme densities of narwhals Monodon monoceros in the offshore pack ice

Laidre, K.L., and M.P. Heide-Jorgensen, "Life in the lead: extreme densities of narwhals Monodon monoceros in the offshore pack ice," Mar. Ecol. Prog. Ser., 423, 269-278, doi:10.3354/meps08941 , 2011.

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10 Feb 2011

There is a paucity of information on abundance, densities, and habitat selection of narwhals Monodon monoceros in the offshore pack ice of Baffin Bay, West Greenland, despite the critical importance of winter foraging regions and considerable sea ice declines in the past decades. We conducted a double-platform visual aerial survey over a narwhal wintering ground to obtain pack ice densities and develop the first fully corrected abundance estimate using point conditional mark-recapture distance sampling. Continuous video recording and digital images taken along the trackline allowed for in situ quantification of winter narwhal habitat and for the estimation of fine-scale narwhal habitat selection and habitat-specific sighting probabilities. Abundance at the surface was estimated at 3484 (coefficient of variation [CV] = 0.46) including whales missed by observers. The fully corrected abundance of narwhals was 18044 (CV = 0.46), or approximately one-quarter of the entire Baffin Bay population. The narwhal wintering ground surveyed (~9500 km²) had 2.4 to 3.2% open water based on estimates from satellite imagery (NASA Moderate Resolution Imaging Spectroradiometer) and 1565 digital photographic images collected on the trackline. Thus, the ~18000 narwhals had access to 233 km² of open water, resulting in an average density of ~77 narwhals km^-2 open water. Narwhal sighting probability near habitats with <10% or 10 to 50% open water was significantly higher than sighting probability in habitats with >50% open water, suggesting narwhals select optimal foraging areas in dense pack ice regardless of open water availability. This study provides the first quantitative ecological data on densities and habitat selection of narwhals in pack ice foraging regions that are rapidly being altered with climate change.

A whale of an opportunity: Examining the vertical structure of chlorophyll-a in high Arctic waters using instrumented marine predators

Laidre, K.L., M.P. Heide-Jorgensen, M.L. Logsdon, L. Delwiche, T.G. Nielsen, "A whale of an opportunity: Examining the vertical structure of chlorophyll-a in high Arctic waters using instrumented marine predators," Mar. Biol. Res., 6, 519-529, doi:10.1080/17451000903505616, 2010.

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6 Nov 2010

Sixty hours of direct measurements of fluorescence were collected from six bowhead whales (Balaena mysticetus) instrumented with fluorometers in Greenland in April 2005 and 2006. The data were used to (1) characterize the three-dimensional spatial pattern of chlorophyll-a (Chl-a) in the water column, (2) to examine the relationships between whale foraging areas and productive zones, and (3) to examine the correlation between whale-derived in situ values of Chl-a and those from concurrent satellite images using the NASA MODIS (Moderate Resolution Imaging Spectroradiometer) EOS-AQUA satellite (MOD21, SeaWifs analogue OC3M and SST MOD37).

Bowhead whales traversed 1600 km², providing information on diving, Chl-a structure and temperature profiles to depths below 200 m. Feeding dives frequently passed through surface waters (>50 m) and targeted depths close to the bottom, and whales did not always target patches of high concentrations of Chl-a in the upper 50 m. Five satellite images were available within the periods whales carried fluorometers. Whales traversed 91 pixels collecting on average 761 s (SD 826) of Chl-a samples per pixel (0–136 m). The depth of the Chl-a maximum ranged widely, from 1 to 66 m. Estimates of Chl-a made from the water-leaving radiance measurements using the OC3M algorithm were highly skewed with most samples estimated as <1 mg m^-3 Chl-a, while data collected from whales had a broad distribution with Chl-a reaching >9 mg m^-3. The correlation between the satellite-derived and whale-derived Chl-a maxima was poor, a linear fit explained only 10% of the variance.

Narwhals document continued warming of southern Baffin Bay

Laidre, K.L., M.P. Heide-Jorgensen, W. Ermold, and M. Steele, "Narwhals document continued warming of southern Baffin Bay," J. Geophys. Res., 115, doi:10.1029/2009JC005820, 2010.

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23 Oct 2010

We report on wintertime data collected from Baffin Bay and northern Davis Strait, a major gateway linking the Arctic with the subpolar North Atlantic, using narwhals (Monodon monoceros) as an oceanographic sampling platform. Fourteen narwhals were instrumented with satellite-linked time-depth-temperature recorders between 2005 and 2007. Transmitters collected and transmitted water column temperature profiles from each dive between December and April, where >90% of maximum daily dive depths reached the bottom. Temperature measurements were combined with 15 helicopter-based conductivity-temperature-depth (CTD) casts taken in April 2007 across central Baffin Bay and compared with hydrographic climatology values used for the region in Arctic climate models. Winter temperature maxima for whale and CTD data were in good agreement, ranging between 4.0 deg C and 4.6 deg C in inshore and offshore Baffin Bay and in Davis Strait. The warm Irminger Water was identified between 57 deg W and 59 deg W (at 68 deg N) between 200 and 400 m depths. Whale data correlated well with climatological temperature maxima; however, they were on average 0.9 deg C warmer plus/minus 0.6 deg C (P < 0.001). Furthermore, climatology data overestimated the winter surface isothermal layer thickness by 50–80 m.

Our results suggest the previously documented warming in Baffin Bay has continued through 2007 and is associated with a warmer West Greenland Current in both of its constituent water masses. This research demonstrates the feasibility of using narwhals as ocean observation platforms in inaccessible Arctic areas where dense sea ice prevents regular oceanographic measurements and where innate site fidelity, affinity for winter pack ice, and multiple daily dives to >1700 m offer a useful opportunity to sample the area.

Abundance of narwhals (Monodon monoceros) on the hunting grounds in Greenland

Heide-Jorgensen, M.P., K.L. Laidre, M.L. Burt, D.L. Borchers, T.A. Marques, R.G. Hansen, M. Rasmussen, and S. Fossette, "Abundance of narwhals (Monodon monoceros) on the hunting grounds in Greenland," J. Mammol., 91, 1135-1151, 2010.

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1 Oct 2010

Narwhals (Monodon monoceros L.) occur in the Atlantic sector of the Arctic where for centuries they have been subject to subsistence hunting by Inuit in Greenland and Canada. Scientific advice on the sustainable levels of removals from narwhal populations provides the basis for quotas implemented in both Greenland and Canada. The scientific advice relies heavily on extensive aerial surveys that are the only feasible way to acquire data on narwhal densities and abundance throughout their range. In some areas lack of information on abundance, in combination with high exploitation levels, has caused conservation concerns leading to restrictions on the international trade in narwhal tusks. Narwhals also are regarded as highly sensitive to habitat disturbance caused by global warming.

This study analyzed data from aerial sighting surveys covering four major narwhal hunting grounds in Greenland. The surveys were conducted as double observer experiments with 2 independent observation platforms, 1 at the front and 1 at the rear of the survey plane. The sighting data were analyzed using mark-recapture distance sampling techniques that allow for correction for whales that were missed by the observers. The surveys also were corrected for animals that were submerged during the passage of the survey plane, using diving and submergence data from satellite-linked time-depth recorders deployed on 2 free-ranging narwhals.

The abundance of narwhals on the wintering ground in West Greenland in 2006 was 7,819 (95% confidence interval [CI]: 4,358–14,029). The abundances of narwhals in Inglefield Bredning and Melville Bay, northwest Greenland in 2007 were 8,368 (95% CI: 5,209–13,442) and 6,024 (95% CI: 1,403–25,860), respectively. The abundance of narwhals in East Greenland in 2008 was 6,444 (95% CI: 2,505–16,575). These surveys provide the first estimates of narwhal abundance from important hunting areas in East and West Greenland and provide larger and more complete estimates from previously surveyed hunting grounds in Inglefield Bredning. The estimates can be used for setting catch limits for the narwhal harvest in West and East Greenland and as a baseline for examining the effects of climate change on narwhal abundance.

Spatial associations between large baleen whales and their prey in West Greenland

Laidre, K.L., M.P. Heide-Jorgensen, P. Heagerty, A. Cossio, B. Bergstrom, and M. Simon, "Spatial associations between large baleen whales and their prey in West Greenland," Mar. Ecol. Prog. Ser., 402, 269-284, doi:10.3354/meps08423, 2010.

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8 Mar 2010

This study combined data on fin whale Balaenoptera physalus, humpback whale Megaptera novaeangliae, minke whale B. acutorostrata, and sei whale B. borealis sightings from large-scale visual aerial and ship-based surveys (248 and 157 sightings, respectively) with synoptic acoustic sampling of krill Meganyctiphanes norvegica and Thysanoessa sp. abundance in September 2005 in West Greenland to examine the relationships between whales and their prey.

Krill densities were obtained by converting relationships of volume backscattering strengths at multiple frequencies to a numerical density using an estimate of krill target strength. Krill data were vertically integrated in 25 m depth bins between 0 and 300 m to obtain water column biomass (g m^-2) and translated to density surfaces using ordinary kriging. Standard regression models (Generalized Additive Modeling, GAM, and Generalized Linear Modeling, GLM) were developed to identify important explanatory variables relating the presence, absence, and density of large whales to the physical and biological environment and different survey platforms.

Large baleen whales were concentrated in 3 focal areas: (1) the northern edge of Lille Hellefiske bank between 65 and 67 deg N, (2) north of Paamiut at 63 deg N, and (3) in South Greenland between 60 and 61 deg N. There was a bimodal pattern of mean krill density between depths, with one peak between 50 and 75 m (mean 0.75 g m^-2, SD 2.74) and another between 225 and 275 m (mean 1.2 to 1.3 g m^-2, SD 23 to19). Water column krill biomass was 3 times higher in South Greenland than at any other site along the coast. Total depth-integrated krill biomass was 1.3 x 10⁹ (CV 0.11).

Models indicated the most important parameter in predicting large baleen whale presence was integrated krill abundance, although this relationship was only significant for sightings obtained on the ship survey. This suggests that a high degree of spatio-temporal synchrony in observations is necessary for quantifying predator–prey relationships. Krill biomass was most predictive of whale presence at depths >150 m, suggesting a threshold depth below which it is energetically optimal for baleen whales to forage on krill in West Greenland.

The effect of sea-ice loss on beluga whales (Delphinapterus leucas) in West Greenland

Heide-Jorgensen, M.P., K.L. Laidre, D. Borchers, T.A. Marques, H. Stern, and M. Simon, "The effect of sea-ice loss on beluga whales (Delphinapterus leucas) in West Greenland," Polar Res., 29, 198-208, 2010.

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14 Jan 2010

An aerial survey was conducted to estimate the abundance of belugas (Delphinapterus leucas) on their wintering ground in West Greenland in March–April 2006 and 2008. The survey was conducted as a double platform aerial line transect survey, and sampled approximately 17% of the total survey area of ca. 125 000 km². The abundance of belugas was 10 595 (95% confidence interval 4904–24 650). The largest abundance was found at the northern part of Store Hellefiske Bank, at the eastern edge of the Baffin Bay pack ice, a pattern similar to that found in eight systematic surveys conducted since 1981.

A clear relationship between decreasing sea-ice cover and increasing offshore distance of beluga sightings was established from all previous surveys, suggesting that belugas expand their distribution westward as new areas on the banks of West Greenland open up earlier in spring with reduced sea-ice coverage or early annual ice recession. This is in contrast to the relatively confined distribution of belugas near the coast in limited open areas in the early 1980s, when sea-ice cover was greater. However, the effects of the changes in coastal availability of belugas can also be observed with the correlation between catches from the local Inuit hunt and sea-ice cover, where the catches increased significantly with increasing sea-ice coverage during the period 1954–2006. These results, based on nearly 30 years of dedicated survey effort, are among the first available evidence showing a shift in distribution of an Arctic cetacean in response to changes in sea-ice coverage.

Sexual segregation of common minke whales (Balaenoptera acutorostrata) and sex ratio of catches in Greenland

Laidre, K.L., P. Heagerty, M.P. Heide-Jorgensen, L. Witting, and M. Simon, "Sexual segregation of common minke whales (Balaenoptera acutorostrata) and sex ratio of catches in Greenland," ICES J. Mar. Sci, 66, 2253-2266, doi:10.1093/icesjms/fsp191, 2009.

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4 Jul 2009

The harvest of common minke whales (Balaenoptera acutorostrata) in West Greenland has historically been skewed towards female whales, yet a complete analysis of spatial and temporal patterns of catch sex ratio has never been conducted. We examined trends in the sex ratio of catches over time, season, space, and relative to sea temperature using 2400 records from inshore Greenland subsistence whaling operations (1960–2006) and 2072 records from offshore Norwegian commercial operations (1968–1985).

Logistic regression models were developed to examine the trend in sex ratio in three regions (Northwest, NW; Central West, CW; Southwest, SW) and by latitude. The highly skewed proportion of females in all catches was strongly positively correlated (r² = 0.8) with latitude in the offshore catches (>100 km). Generalized linear models of inshore catches indicated slightly increasing though non-significant trends in the proportion of females taken off CW and NW Greenland and a significant declining trend off SW Greenland. Sensitivity analyses show that the declining inshore SW trend was entirely accounted for by the past 5 years (2002–2006) of data. Models containing both year and temperature interactions suggested that either parameter provided an equivalent explanation of the variation in trends across regions.

A novel method for identifying behavioral changes in animal movement data

Gurarie, E., R. Andrews, and K.L. Laidre, "A novel method for identifying behavioral changes in animal movement data," Ecol. Lett., 12, 395-408, 2009.

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1 May 2009

A goal of animal movement analysis is to reveal behavioural mechanisms by which organisms utilize complex and variable environments. Statistical analysis of movement data is complicated by the fact that the data are multidimensional, autocorrelated and often marked by error and irregular measurement intervals or gappiness. Furthermore, movement data reflect behaviours that are themselves heterogeneous.

Here, we model movement data as a subsampling of a continuous stochastic processes, and introduce the behavioural change point analysis (BCPA), a likelihood-based method that allows for the identification of significant structural changes. The BCPA is robust to gappiness and measurement error, computationally efficient, easy to implement and reveals structure that is otherwise difficult to discern. We apply the analysis to a GPS movement track of a northern fur seal (Callorhinus ursinus), revealing an unexpectedly complex diurnal behavioural profile, and demonstrate its robustness to the greater errors associated with the ARGOS tracking system. By informing empirical interpretation of movement data, we suggest that the BCPA can eventually motivate the development of mechanistic behavioural models.

Bowhead whale springtime song off West Greenland

Stafford, K.M., S.E. Moore, K.L. Laidre, and M.P. Heide-Jorgensen, "Bowhead whale springtime song off West Greenland," J. Acoust. Soc. Am., 124, 1-9, doi:10.1121/1.2980443, 2008.

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1 Nov 2008

Three songs were recorded from bowhead whales (Balaena mysticetus) in Disko Bay, West Greenland, during 59 h of recordings via sonobuoys deployed on seven days between 5 and 14 April 2007. Song elements were defined by units following the protocol of previous description of bowhead whale song. The two most prominent songs were loud, complex, and repeated in long bouts on multiple recording days while the third song was much simpler and recorded on only one day.

Bowhead whale simple calls and faint song elements were also recorded using digital audio tape recorders and a dipping hydrophone deployed from the sea ice approximately 100–150 km southwest of Disko Bay on three separate days suggesting that song is also produced in the central portion of Baffin Bay in winter. Songs recorded in Disko Bay are from an area where approximately 85% of the whales have been determined to be adult females. Although it is not known which sex was singing, we speculate that, as in humpback whales (Megaptera novaeangliae), male bowhead whales may sing to mediate sexual competition or mate selection behaviors. This is the first detailed description of springtime songs for bowhead whales in the eastern Arctic.

Latitudinal gradients in sea ice and primary production determine Arctic seabird colony size in Greenland

Laidre, K.L., M.P. Heide-Jorgensen, J. Nyeland, A. Mosbech, and B. Doertmann, "Latitudinal gradients in sea ice and primary production determine Arctic seabird colony size in Greenland," Proc. R. Soc. B, Biol. Sci., 275, 2695-2702, doi:10.1098/rspb.2008.0874, 2008.

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19 Aug 2008

Sea ice loss will indirectly alter energy transfer through the pelagic food web and ultimately impact apex predators. We quantified spring-time trends in sea ice recession around each of 46 thick-billed murre (Uria lomvia) colonies in west Greenland across 20° of latitude and investigated the magnitude and timing of the associated spring-time primary production. A geographical information system was used to extract satellite-based observations of sea ice concentration from the Nimbus-7 scanning multichannel microwave radiometer (SMMR, 1979–1987) and the Defence Meteorological Satellite Programs Special Sensor Microwave/Imager (SSMI, 1987–2004), and satellite-based observations of chlorophyll a from the moderate resolution imaging spectroradiometer (MODIS: EOS-Terra satellite) in weekly intervals in circular buffers around each colony site (150 km in radius).

Rapid recession of high Arctic seasonal ice cover created a temporally predictable primary production bloom and associated trophic cascade in water gradually exposed to solar radiation. This pattern was largely absent from lower latitudes where little to no sea ice resulted in a temporally variable primary production bloom driven by nutrient cycling and upwelling uncoupled to ice. The relationship between the rate and variability of sea ice recession and colony size of thick-billed murres shows that periodical confinement of the trophic cascade at high latitudes determines the carrying capacity for Arctic seabirds during the breeding period.

Quantifying the sensitivity of arctic marine mammals to climate-induced habitat change

Laidre, K.L., I. Sitrling, L. Lowry, Wiig, M.P. Heide-Jrgensen, and S. Ferguson, "Quantifying the sensitivity of arctic marine mammals to climate-induced habitat change," Ecol. Appl., 18, S97-S125, 2008.

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1 Mar 2008

We review seven Arctic and four subarctic marine mammal species, their habitat requirements, and evidence for biological and demographic responses to climate change. We then describe a pan-Arctic quantitative index of species sensitivity to climate change based on population size, geographic range, habitat specificity, diet diversity, migration, site fidelity, sensitivity to changes in sea ice, sensitivity to changes in the trophic web, and maximum population growth potential (R_max). The index suggests three types of sensitivity based on: (1) narrowness of distribution and specialization in feeding, (2) seasonal dependence on ice, and (3) reliance on sea ice as a structure for access to prey and predator avoidance. Based on the index, the hooded seal, the polar bear, and the narwhal appear to be the three most sensitive Arctic marine mammal species, primarily due to reliance on sea ice and specialized feeding. The least sensitive species were the ringed seal and bearded seal, primarily due to large circumpolar distributions, large population sizes, and flexible habitat requirements. The index provides an objective framework for ranking species and focusing future research on the effects of climate change on Arctic marine mammals. Finally, we distinguish between highly sensitive species and good indicator species and discuss regional variation and species-specific ecology that confounds Arctic-wide generalization regarding the effects of climate change.

Using narwhals as oceanographic sampling platforms in the high Arctic

Laidre, K.L., and M.P. Heide-Jorgensen, "Using narwhals as oceanographic sampling platforms in the high Arctic," Oceanography, 20, 30-35, 2007.

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1 Dec 2007

Offshore Arctic waters are the most remote and unexplored areas of the Northern Hemisphere. Generally covered by sea ice for most of the year, these waters are characterized by darkness for up to six months and inhospitable temperatures reaching -40°C in mid-winter. With few exceptions, offshore Arctic ecosystems are logistically difficult, or sometimes impossible, to observe with traditional platforms like vessels or airplanes, which can be impacted by severe environmental conditions. Oceanographers are increasingly relying on data collection from nontraditional platforms adapted to the Arctic to investigate major scientific questions about ecosystem changes in the Arctic Ocean.

Role of the bowhead whale as a predator in West Greenland

Laidre, K.L., M.P. Heide-Jorgensen, and T.G. Nielsen, "Role of the bowhead whale as a predator in West Greenland," Mar. Ecol. Prog. Ser., 346, 285-297, 2007.

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27 Sep 2007

We examined the spatial and temporal linkage between primary production, zooplankton distribution and density, and bowhead whale Balaena mysticetus foraging behavior in Disko Bay, West Greenland using concurrent ship-based oceanographic and net sampling together with instrumentation of whales with satellite-linked transmitters and dive recorders. Estimates of bowhead whale abundance were used in a bioenergetic model to calculate the potential consumption of zooplankton during their 4 mo stay in Disko Bay. Between 2001 and 2006, 30 whales were fitted with satellite transmitters that provided information on daily movements, and 14 whales were tracked with archival time–depth or time–depth–fluorescence recorders that provided detailed dive data. Simultaneous data were collected on water column structure, phytoplankton and zooplankton density, taxa and biomass at 25 stations south of Disko Island in 2003, 2005 and 2006.

After the retreat of annual winter sea ice, bowhead whales explored a limited area along the south coast of Disko Island and had high interannual site fidelity. Mean dive depths varied between 53 (SD = 35) and 109 (SD = 41) m but maximum dive depths were >400 m. Most dives targeted the bottom and dive durations >40 min were observed for several whales. Available prey for bowhead whales was dominated by calanoid copepods, with Calanus finmarchicus, C. glacialis and C. hyperboreus occurring at 90 to 100% of all stations between 0 and 50 m and contributing 78 ± 25% of the total biomass. Bottom sampling for epizooplankton in 2006 resulted in unprecedented densities of C. finmarchicus, several orders of magnitude higher than at any other depth. Bioenergetic modeling indicated the population consumes ~220 US t of zooplankton per day or >21000 t during the 4 mo stay in Disko Bay. Although the total biomass of zooplankton in the upper 50 m of the water column theoretically could support this predation level, benthic zooplankton densities and behavioral data suggest whales target preascension stage epibenthic copepods in high density patches.

Dynamics of the sea ice edge in Davis Strait

Heide-Jørgensen, M.P., H. Stern, and K.L. Laidre, "Dynamics of the sea ice edge in Davis Strait," J. Mar. Syst., 67, 170-178, doi:10.1016/j.jmarsys.2006.10.011, 2007.

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1 Aug 2007

Sea ice concentration derived from satellite data were used to quantify sea ice characteristics in the Baffin Bay–Davis Strait–Labrador Sea area. The ice edge in Davis Strait extends from Disko Bay in West Greenland 2500 km south to Newfoundland. The mean intercept at the West Greenland coast between 1979 and 2002 was located at 66.9°N, assuming the ice edge was 85% ice concentration. The shallow banks of West Greenland (> 200 m) had, on average, an ice extent covering 30 to 100% of the bank area during March for the 24 year time series. This extent varied in concentration between 39 and 100%. However, intermediate ice concentrations (39–85% ice concentration) covered on average 25% of the banks. The Davis Strait ice edge showed considerable interannual variation correlated with the winter index of the North Atlantic Oscillation and the Arctic Oscillation. No temporal trend in ice extent could be detected over the 24 years. In addition to the ice production on the banks of West Greenland, sea ice produced further north in Baffin Bay was advected to the banks as shown by satellite tracked drifting buoys. Both the local sea ice production and the advected sea ice contributed significantly to sea temperatures and salinities measured during summer on the banks. No correlation between sea ice concentration and plankton abundance could be detected but the recruitment of the offshore cod (Gadus morhua) component in South Greenland was negatively correlated to the amount of sea ice in Baffin Bay.

Increasing abundance of bowhead whales in West Greenland

Heide-Jørgensen, M.P., K.L. Laidre, D. Borchers, F. Samara, and H. Stern, "Increasing abundance of bowhead whales in West Greenland," Biol. Lett., 3, 577-580, 2007.

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1 Aug 2007

In April 2006, a dedicated survey of bowhead whales (Balaena mysticetus) was conducted on the former whaling ground in West Greenland to determine the current wintering population abundance. This effort included a double platform aerial survey design, satellite tracking of the movements of nine whales, and estimation of high-resolution surface time from 14 whales instrumented with time–depth recorders. Bowhead whales were estimated to spend an average of 24% (cv=0.03) of the time at or above 2 m depth, the maximum depth at which they can be seen on the trackline. This resulted in a fully corrected abundance estimate of 1229 (95% CI: 495–2939) bowhead whales when the availability factor was applied and sightings missed by observers were corrected. This surprisingly large population estimate is puzzling given that the change in abundance cannot be explained by a recent or rapid growth in population size. One possible explanation is that the population, which demonstrates high age and sex segregation, has recently attained a certain threshold size elsewhere, and a higher abundance of mature females appears on the winter and spring feeding ground in West Greenland. This in combination with the latest severe reduction in sea ice facilitating access to coastal areas might explain the surprising increase in bowhead whale abundance in West Greenland.

Springtime coupling between chlorophyll a, sea ice and sea surface temperature in Disko Bay, West Greenland

Heide-Jorgensen, M.P., K.L. Laidre, M.L. Logsdon, and T.G. Nielsen, "Springtime coupling between chlorophyll a, sea ice and sea surface temperature in Disko Bay, West Greenland," Prog. Oceanogr., 73, 79-95, doi:10.1016/j.pocean.2007.01.006, 2007.

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1 Apr 2007

Alterations in sea ice and primary production are expected to have cascading influences on the food web in high Arctic marine ecosystems. This study spanned four years and examined the spring phytoplankton production bloom in Disko Bay, West Greenland (69°N, 53°W) (using chlorophyll a concentrations as a proxy) under contrasting sea ice conditions in 2001 and 2003 (heavy sea ice) and 2002 and 2004 (light sea ice). Satellite-based observations of chlorophyll a, sea ice and sea surface temperature were used together with in situ depth profiles of chlorophyll a fluorescence collected at 24 sampling stations along the south coast of Disko Island (5–30 km offshore) in May 2003 and 2004. Chlorophyll a and sea surface temperatures were also obtained from the Moderate Resolution Imaging Spectroradiometer (MODIS: EOS-Terra and AQUA satellites) between March 2001 and July 2004. Daily SMMR/SSMI sea ice data were obtained in the same years. An empirical regional algorithm was developed to calibrate ratios of remotely sensed measurements of water leaving radiance with in situ chlorophyll a fluorescence. The optimal integration depth was 0–4 m, explaining between 70% and 91% of the variance. The spatial development of the phytoplankton bloom showed that the southwestern corner of the study area had the earliest and the largest spring phytoplankton bloom. The eastern part of Disko Bay, influenced by meltwater outflow from the glaciers, shows no signs of an early phytoplankton bloom and followed the general pattern of an accelerated bloom soon after the disappearance of sea ice. In all four years the coupling between phytoplankton and sea ice was bounded by average open water between 50% and 80%, likely due to the combined availability of light and stable open water. The daily incremental growth in both mean chlorophyll a density (chlorophyll a per volume water, μg l^-1) and abundance (density of chlorophyll a extrapolated to ice free areas, tons) estimated by linear regression (chlorophyll a vs. day) between 1 April and 15 May was highest in 2002 and 2004 (light ice years) and lowest in 2001 and 2003 (heavy ice years). In years with late sea ice retreat the chlorophyll a attained only slightly lower densities than in years with early sea ice retreat. However, the abundance of chlorophyll a in light ice years was considerably larger than in heavy ice years, and there was an obvious effect of more open water for light-induced stimulation of primary production. This observation demonstrates the importance of estimating chlorophyll a abundance rather than density in sea ice covered areas. This study also presents the first regional calibration of MODIS chlorophyll a data for Arctic waters.

Patterns of growth and body condition in sea otters from the Aleutian archipelago before and after the recent population decline

Laidre, K.L., J.A. Estes, M.T. Tinker, J. Bodkin, D. Monson, and K. Schneider, "Patterns of growth and body condition in sea otters from the Aleutian archipelago before and after the recent population decline," J. Animal Ecol., 75, 978-989, doi:10.1111/j.1365-2656.2006.01117.x, 2006.

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1 Jul 2006

Growth models for body mass and length were fitted to data collected from 1842 sea otters Enhydra lutris shot or live-captured throughout south-west Alaska between 1967 and 2004. Growth curves were constructed for each of two main year groups: 1967–71 when the population was at or near carrying capacity and 1992–97 when the population was in steep decline. Analyses of data collected from animals caught during 2004, when the population density was very low, were precluded by a small sample size and consequently only examined incidentally to the main growth curves.

Growth curves demonstrated a significant increase in body mass and body length at age in the 1990s. Asymptotic values of body mass were 12–18% higher in the 1990s than in the 1960s/70s, and asymptotic values for body length were 10–1% higher between the same periods. Data collected in 2004 suggest a continued increase in body size, with nearly all data points for mass and length falling significantly above the 1990s growth curves.

In addition to larger asymptotic values for mass and length, the rate of growth towards asymptotic values was more rapid in the 1990s than in the 1960s/70s: sea otters reached 95% of asymptotic body mass and body length 1–2 years earlier in the 1990s.

Body condition (as measured by the log mass/log length ratio) was significantly greater in males than in females. There was also an increasing trend from the 1960s/70s through 2004 despite much year-to-year variation.

Population age structures differed significantly between the 1960s/70s and the 1990s with the latter distribution skewed toward younger age classes (indicating an altered l_x function) suggesting almost complete relaxation of age-dependent mortality patterns (i.e. those typical of food-limited populations).

This study spanned a period of time over which the population status of sea otters in the Aleutian archipelago declined precipitously from levels at or near equilibrium densities at some islands in the 1960s/70s to < 5% of estimated carrying capacity by the late 1990s. The results of this study indicate an improved overall health of sea otters over the period of decline and suggest that limited nutritional resources were not the cause of the observed reduced population abundance. Our findings are consistent with the hypothesis that the decline was caused by increased killer whale predation.

Trends in sea ice cover within habitats used by bowhead whales in the western Arctic

Moore, S.E., and K.L. Laidre, "Trends in sea ice cover within habitats used by bowhead whales in the western Arctic," Ecolog. Appl., 16, 932-944, 2006.

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1 Jun 2006

We examined trends in sea ice cover between 1979 and 2002 in four months (March, June, September, and November) for four large (approximately 100,000 km²) and 12 small (approximately 10,000 km²) regions of the western Arctic in habitats used by bowhead whales (Balaena mysticetus). Variation in open water with year was significant in all months except March, but interactions between region and year were not. Open water increased in both large and small regions, but trends were weak with least-squares regression accounting for < or =34% of the total variation. In large regions, positive trends in open water were strongest in September. Linear fits were poor, however, even in the East Siberian, Chukchi, and Beaufort seas, where basin-scale analyses have emphasized dramatic sea ice loss. Small regions also showed weak positive trends in open water and strong interannual variability.

Open water increased consistently in five small regions where bowhead whales have been observed feeding or where oceanographic models predict prey entrainment, including: (1) June, along the northern Chukotka coast, near Wrangel Island, and along the Beaufort slope; (2) September, near Wrangel Island, the Barrow Arc, and the Chukchi Borderland; and (3) November, along the Barrow Arc. Conversely, there was very little consistent change in sea ice cover in four small regions considered winter refugia for bowhead whales in the northern Bering Sea, nor in two small regions that include the primary springtime migration corridor in the Chukchi Sea. The effects of sea ice cover on bowhead whale prey availability are unknown but can be modeled via production and advection pathways. Our conceptual model suggests that reductions in sea ice cover will increase prey availability along both pathways for this population. This analysis elucidates the variability inherent in the western Arctic marine ecosystem at scales relevant to bowhead whales and contrasts basin-scale depictions of extreme sea ice retreats, thinning, and wind-driven movements.

Dissolving stock discreteness with satellite tracking: Bowhead whales in Baffin Bay

Heide-Jorgensen, M.P., K.L. Laidre, M.V. Jensen, L. Dueck, and L.D. Postma, "Dissolving stock discreteness with satellite tracking: Bowhead whales in Baffin Bay," Mar. Mammal Sci., 22, 34-45, doi: 10.1111/j.1748-7692.2006.00004.x, 2006.

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10 Jan 2006

Nine bowhead whales (Balaena mysticetus) were instrumented with satellite transmitters in West Greenland in May 2002 and 2003. Transmitters were either encased in steel cans or imbedded in floats attached to wires. Transmitters mounted in steel cans had a high initial failure rate, yet those that were successful provided tracking durations up to seven months. Float tags had a low initial failure rate and initially provided large numbers of positions; however, they had deployment durations of only 2–33 d. All tracked whales departed from West Greenland and headed northwest towards Lancaster Sound in the end of May. Three tags with long tracking durations (197–217 d) recorded movements of whales (1 male, 2 females) into December in 2002 and 2003. All of these individuals remained within the Canadian High Arctic or along the east coast of Baffin Island in summer and early fall. By the end of October, all three whales moved rapidly south along the east coast of Baffin Island and entered Hudson Strait, an apparent wintering ground for the population. One of the whales did not visit Isabella Bay on east Baffin Island, the locality used for abundance estimation from photographic reidentification of individuals. The movements of whales tagged in this study raise critical questions about the assumed stock discreteness of bowhead whales in Foxe Basin, Hudson Strait, and Davis Strait and indicate current estimates of abundance are negatively biased.