Spatial and temporal variation in the diets of polar bears across the Canadian Arctic: indicators of changes in prey populations and environment

Iverson, Sara J.; Stirling, Ian; Lang, Shelley L. C.

doi:10.1017/cbo9780511541964.008

Cited by 64 publications

(87 citation statements)

References 25 publications

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“…However, a similar regional trend was observed by Thiemann et al (2007a), who found higher levels of a specific bearded seal FA biomarker in Southern Beaufort Sea bears than in the northern subpopulation. Iverson et al (2006) also found higher bearded seal consumption among polar bears sampled in the Southern Beaufort Sea between 1972 and 1991.…”

Section: Regional Differences In Polar Bear Dietsmentioning

confidence: 65%

“…Iverson et al (2006) those samples (i.e., new diet estimates were generated) using a more complete modeling data set (see QFASA modeling, below) and greatly expanded the temporal, spatial, and intraspecific scope of the investigation. To control for longer-term temporal trends, regional and demographic differences were tested using a single sample (the most recent) from each bear handled between 1999 and 2004 (n ¼ 1488 bears).…”

Section: Sample Collectionmentioning

confidence: 99%

“…We scaled FA contributions by prey body mass (relative to the smallest prey, ringed seals) to estimate the relative number of individuals of each species consumed ( Fig. 5; see Iverson et al 2006). The following average body-mass values were used for scaling: ringed seal (65 kg), bearded seal (300 kg), harbor seal (87 kg), harp seal (110 kg), hooded seal (250 kg), walrus (1040 kg), beluga whale (1500 kg), and narwhal (1300 kg).…”

Section: Simulation Studiesmentioning

confidence: 99%

“…Studies to date suggest that polar bears feed primarily on ringed seals (Phoca hispida), and to a lesser extent on bearded seals (Erignathus barbatus; Stirling 1974, Stirling and McEwan 1975, Stirling and Archibald 1977, Smith 1980, Stirling and Øritsland 1995, both of which are available throughout the Canadian Arctic. However, more recent studies by and Iverson et al (2006) have indicated that harp seals (Pagophilus groenlandica) may also be important prey in areas where they are available. Opportunistic observations have also identified a wide diversity of apparently less important food items including beluga whales (Delphinapterus leucas; Freeman 1973, Heyland and Hey 1976, Lowry et al 1987, Smith and Sjare 1990, narwhals (Monodon monoceros; Smith and Sjare 1990), walruses (Odobenus rosmarus; Calvert and Stirling 1990), and even conspecifics (Taylor et al 1985, Amstrup et al 2006, Stone and 3 Present address: Department of Biological Sciences, University of Alberta, Edmonton, Alberta T6G 2E9 Canada.…”

Section: Introductionmentioning

confidence: 99%

“…Earlier summer break-up of the sea ice in Western Hudson Bay over the last 30 years (Stirling et al 1999, Gough et al 2004, Gagnon and Gough 2005) is strongly correlated with declines in polar bear body condition, natality, survival, and population size Parkinson 2006, Regehr et al 2007). Iverson et al (2006) reported a decrease in ringed seal consumption among Western Hudson Bay polar bears between 1994 and 1998 that correlated with increasingly early spring ice retreat. More recent changes in polar bear diets in Western Hudson Bay, and elsewhere, remain unknown.…”

Section: Introductionmentioning

confidence: 99%

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Polar Bear Diets and Arctic Marine Food Webs: Insights From Fatty Acid Analysis

Thiemann

Iverson

Stirling³

2008

Ecological Monographs

306

307

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Abstract. We used quantitative fatty acid signature analysis (QFASA) to examine the diets of 1738 individual polar bears (Ursus maritimus) sampled across the Canadian Arctic over a 30-year span. Polar bear foraging varied over large and small spatial and temporal scales, and between demographic groups. Diets in every subpopulation were dominated by ringed seals (Phoca hispida) and, in the eastern Arctic, secondarily by harp seals (Pagophilus groenlandica). Beluga whales (Delphinapterus leucas) were an important food source for bears in the High Arctic, which is consistent with previous anecdotal reports. Foraging patterns were most similar among neighboring subpopulations with similar prey assemblages, but also differed geographically within Western Hudson Bay. The sexual size dimorphism of polar bears had an important effect on foraging, as large bearded seals (Erignathus barbatus) and walruses (Odobenus rosmarus) were consumed most often by older, male bears, whereas ringed seals and, where available, harbor seals (P. vitulina) were most important to younger age classes. Larger, older bears also had the greatest dietary diversity, apparently because of their ability to include larger-bodied prey. During spring and summer, polar bears in some areas increased predation on migratory harp seals and beluga whales. In Western Hudson Bay, bearded seal consumption declined between 1995 and 2001 for both male and female bears and continued to decline among females up to the most recent sampling (2004). Ringed seal consumption in Western Hudson Bay increased between 1998 and 2001, perhaps in response to increased ringed seal productivity, but was not significantly affected by date of sea-ice breakup. Overall, our data indicate that polar bears are capable of opportunistically altering their foraging to take advantage of locally abundant prey, or to some degree compensating for a decline in a dominant prey species. However, in other areas polar bears are dependent on the availability of ringed and bearded seals. Recent population data suggest that polar bears with the most specialized diets may be most vulnerable to climate-related changes in ice conditions. The results of this large-scale, ecosystem-based study indicate a complex relationship between sea-ice conditions, prey population dynamics, and polar bear foraging.

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Section: Regional Differences In Polar Bear Dietsmentioning

confidence: 65%

Section: Sample Collectionmentioning

confidence: 99%

Section: Simulation Studiesmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Polar Bear Diets and Arctic Marine Food Webs: Insights From Fatty Acid Analysis

Thiemann

Iverson

Stirling³

2008

Ecological Monographs

306

307

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Population substructure and space use of Foxe Basin polar bears

Sahanatien

Peacock

Derocher

2015

Ecology and Evolution

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Climate change has been identified as a major driver of habitat change, particularly for sea ice-dependent species such as the polar bear (Ursus maritimus). Population structure and space use of polar bears have been challenging to quantify because of their circumpolar distribution and tendency to range over large areas. Knowledge of movement patterns, home range, and habitat is needed for conservation and management. This is the first study to examine the spatial ecology of polar bears in the Foxe Basin management unit of Nunavut, Canada. Foxe Basin is in the mid-Arctic, part of the seasonal sea ice ecoregion and it is being negatively affected by climate change. Our objectives were to examine intrapopulation spatial structure, to determine movement patterns, and to consider how polar bear movements may respond to changing sea ice habitat conditions. Hierarchical and fuzzy cluster analyses were used to assess intrapopulation spatial structure of geographic position system satellite-collared female polar bears. Seasonal and annual movement metrics (home range, movement rates, time on ice) and home-range fidelity (static and dynamic overlap) were compared to examine the influence of regional sea ice on movements. The polar bears were distributed in three spatial clusters, and there were differences in the movement metrics between clusters that may reflect sea ice habitat conditions. Within the clusters, bears moved independently of each other. Annual and seasonal home-range fidelity was observed, and the bears used two movement patterns: on-ice range residency and annual migration. We predict that home-range fidelity may decline as the spatial and temporal predictability of sea ice changes. These new findings also provide baseline information for managing and monitoring this polar bear population.

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Dietary habits of polar bears in Foxe Basin, Canada: possible evidence of a trophic regime shift mediated by a new top predator

Galicia

Thiemann

Dyck

et al. 2016

Ecology and Evolution

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Polar bear (Ursus maritimus) subpopulations in several areas with seasonal sea ice regimes have shown declines in body condition, reproductive rates, or abundance as a result of declining sea ice habitat. In the Foxe Basin region of Nunavut, Canada, the size of the polar bear subpopulation has remained largely stable over the past 20 years, despite concurrent declines in sea ice habitat. We used fatty acid analysis to examine polar bear feeding habits in Foxe Basin and thus potentially identify ecological factors contributing to population stability. Adipose tissue samples were collected from 103 polar bears harvested during 2010–2012. Polar bear diet composition varied spatially within the region with ringed seal (Pusa hispida) comprising the primary prey in northern and southern Foxe Basin, whereas polar bears in Hudson Strait consumed equal proportions of ringed seal and harp seal (Pagophilus groenlandicus). Walrus (Odobenus rosmarus) consumption was highest in northern Foxe Basin, a trend driven by the ability of adult male bears to capture large‐bodied prey. Importantly, bowhead whale (Balaena mysticetus) contributed to polar bear diets in all areas and all age and sex classes. Bowhead carcasses resulting from killer whale (Orcinus orca) predation and subsistence harvest potentially provide an important supplementary food source for polar bears during the ice‐free period. Our results suggest that the increasing abundance of killer whales and bowhead whales in the region could be indirectly contributing to improved polar bear foraging success despite declining sea ice habitat. However, this indirect interaction between top predators may be temporary if continued sea ice declines eventually severely limit on‐ice feeding opportunities for polar bears.

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Spatial and temporal variation in the diets of polar bears across the Canadian Arctic: indicators of changes in prey populations and environment

Cited by 64 publications

References 25 publications

Polar Bear Diets and Arctic Marine Food Webs: Insights From Fatty Acid Analysis

Polar Bear Diets and Arctic Marine Food Webs: Insights From Fatty Acid Analysis

Population substructure and space use of Foxe Basin polar bears

Dietary habits of polar bears in Foxe Basin, Canada: possible evidence of a trophic regime shift mediated by a new top predator

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