Pacific walrus use of higher trophic level prey and the relation to sea ice extent, body condition, and trichinellosis

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Show simple item record Seymour, Jill-Marie 2014-10-25T00:29:45Z 2014-10-25T00:29:45Z 2014-05
dc.description Thesis (Ph.D.) University of Alaska Fairbanks, 2014
dc.description.abstract The changing Arctic ecosystem may prompt Pacific walruses (Odobenus rosmarus divergens) to change their usual diet of lower trophic level prey (e.g., benthic invertebrates) by increasing the consumption of higher trophic level prey (HTLP). Prey-switching may have consequences to walrus populations through increased energetic costs, increased stress response, declines in body condition, and exposure to diseases, including the zoonotic parasite Trichinella spp. Trichinella is possibly transmitted to walruses via predation or scavenging on seals. The goal of this study was to quantify reliance on HTLP using stable carbon and nitrogen isotope ratios, and assess potential correlations among consumption of HTLP and sea ice extent, sex, Trichinella infection, body lipid stores, and cortisol concentrations used as an index of the stress response. Walrus diet is comprised of ~1-22% HTLP and reliance on HTLP may be correlated with sea ice extent in a complex way. Trichinella was present in ringed seal (Pusa hispida, 1/57), Arctic fox (Vulpes lagopus, 3-7/32), and polar bear (Ursus maritimus, 1/1), but was not detected in walruses (0/137) regardless of %HTLP in the diet. Walrus blubber and attached skin contained 44.6 ±12.4% lipid wet weight, which was lower than that found for other Arctic marine mammals; however, the inclusion of skin likely decreased our %lipid values. While the absolute value of %lipid from blubber and attached skin was not a suitable substitute for %lipid from blubber only, we were still able to detect the influence of biological factors, with sex-linked variability in walrus lipid stores observed. Cortisol analysis from full-thickness blubber resulted in a wide range of concentrations (2.77 to 34.04 ng/g), but showed that this stress hormone can be extracted from blubber. While neither %lipid nor blubber cortisol was correlated with the proportion of HTLP in walrus diet, they may serve as minimally-invasive methods for health monitoring of walruses. Overall, dietary plasticity of walruses is robust and switching to HTLP is not likely to have immediate adverse effects on the Pacific walrus population.
dc.description.tableofcontents Chapter 1. General introduction -- Chapter 2. Occurence and genotypic analysis of Trichinella in Alaska marine-associated mammals of the Bering and Chukchi Seas -- Chapter 3. Proportions of higher trophic level prey in the diet of Pacific Walruses -- Chapter 4. Internal-annual variability in the proportional contribution of higher trophic levels to the diet of Pacific Walruses -- Chapter 5. Influence of diet on Lipid content and cortisol contration in blubber of adult Pacific walruses -- Chapter 6. General conclusion.
dc.title Pacific walrus use of higher trophic level prey and the relation to sea ice extent, body condition, and trichinellosis
dc.type Thesis phd
dc.identifier.department Program in Marine Science and Limnology
dc.contributor.chair Horstmann-Dehn, Lara
dc.contributor.committee Atkinson, Shannon
dc.contributor.committee Barboza, Perry
dc.contributor.committee Rosa, Cheryl
dc.contributor.committee Sheffield, Gay
dc.contributor.committee Wooller, Matthew

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