2 results
5 - Linking predator foraging behaviour and diet with variability in continental shelf ecosystems: grey seals of eastern Canada
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- By W. D. Bowen, Marine Fish Division, Bedford Institute of Oceanography, Department of Fisheries and Oceans, Dartmouth, Nova Scotia, Canada B2Y 1A, C. A. Beck, Alaska Department of Fish and Game, Division of Wildlife Conservation, Marine Mammals Section, Anchorage, Alaska 99518, S. J. Iverson, Dalhousie University, Halifax, Nova Scotia, Canada B3H 4J1, D. Austin, Dalhousie University, Halifax, Nova Scotia, Canada B3H 4J1, J. I. MCMillan, Marine Fish Division, Bedford Institute of Oceanography, Department of Fisheries and Oceans, Dartmouth, Nova Scotia, Canada B2Y 1A
- Edited by I. L. Boyd, University of St Andrews, Scotland, S. Wanless, NERC Centre for Ecology and Hydrology, UK
- C. J. Camphuysen, Royal Netherlands Institute for Sea Research
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- Book:
- Top Predators in Marine Ecosystems
- Published online:
- 31 July 2009
- Print publication:
- 11 May 2006, pp 63-81
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- Chapter
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Summary
Upper-trophic-level marine predators are presumed to respond to environmental variability. However, the nature of these responses has been studied in few pinnipeds, particularly during the non-breeding season. Between 1992 and 2003, we measured a suite of behavioural, dietary and life-history variables in grey seals; variables which were expected to vary in response to changes in prey availability. We found significant inter-annual variation in some diving variables indicative of foraging effort and in the species composition of their diets. Postpartum body mass of adult females did not vary inter-annually, but duration of offspring investment (lactation length), total energy investment (offspring weaning mass) and the difference in weaning mass of male and female pups did. There was considerable inter-annual variation in the estimated biomass of grey seal prey species from summer bottom-trawl surveys; however, there was little correlation between grey seal response variables with those estimates. There could be several reasons for this result, but three stand out. First, grey seal numbers on the Scotian Shelf have increased exponentially over the past four decades, implying overall favourable environmental conditions. Grey seals may have adjusted their behaviour and diet to account for variability in prey characteristics other than biomass. Secondly, foraging grey seals and their prey were not sampled at the same time of year. Finally, trends in the biomass of many of the species eaten by grey seals are poorly estimated, thus limiting our understanding of predator responses to ecosystem state.
7 - Spatial and temporal variation in the diets of polar bears across the Canadian Arctic: indicators of changes in prey populations and environment
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- By S. J. Iverson, Dalhousie University, Halifax, Nova Scotia, Canada B3H 4J1, I. Stirling, Canadian Wildlife Service, Edmonton, Alberta, Canada T6H 3S5, S. L. C. Lang, Dalhousie University, Halifax, Nova Scotia, Canada B3H 4J1
- Edited by I. L. Boyd, University of St Andrews, Scotland, S. Wanless, NERC Centre for Ecology and Hydrology, UK
- C. J. Camphuysen, Royal Netherlands Institute for Sea Research
-
- Book:
- Top Predators in Marine Ecosystems
- Published online:
- 31 July 2009
- Print publication:
- 11 May 2006, pp 98-117
-
- Chapter
- Export citation
-
Summary
Polar bears (Ursus maritimus) are broadly distributed in the Arctic and, as such, have the potential to provide information about changes in ecosystem structure and functioning over broad scales in time and space. Yet, because they are so wide-ranging and difficult to observe, there are few quantitative data on polar bear diets or on the ecological (e.g. climate change) and demographic factors that influence prey selection. We used quantitative fatty acid signature analysis of polar bear adipose tissue to estimate their diets in the 1980s/90s across three major regions of the Canadian Arctic: Davis Strait (n = 70), western Hudson Bay (n = 217) and the Beaufort Sea (n = 34), using a database of the major prey species in each region (n = 292). Although polar bears consumed ringed and bearded seals throughout their range, diets differed greatly among regions. Ringed seals accounted for ≥98% of diet in the Beaufort Sea. In western Hudson Bay, ringed seals accounted for about 80% of intake in the early 1990s, indicating the importance of foraging in ice-covered habitat. However, ringed seal consumption declined throughout the 1990s concurrent with progressively earlier ice breakup, while the proportions of bearded and harbour seals increased, suggesting reduced reliance on ice. Throughout Davis Strait, harp seals comprised 50% of bears' diets, consistent with the increase in the harp seal population in this region. Off southern Labrador near the whelping patch, harp seals accounted for 90% of diets.