Isotopic niche, trace element concentrations, and fatty acids in Pacific walrus tissues.

Abstract

Pacific walruses (Odobenus rosmarus divergens) are a culturally and ecologically important species in the Arctic. Walruses are dependent on sea ice cover for breeding, pupping, and resting between foraging bouts. Recent Arctic warming has altered walrus access to sea ice and this may have profound effects on the population. A lack of sea ice cover may limit walrus access to preferred foraging areas or result in shifts in prey consumption. This dissertation focuses on markers of foraging and physiology that can be measured in walrus tissue, including analysis of toxic and essential trace elements, stable isotopic niche, and fatty acids. Concentrations of toxic elements in walrus muscle were low. Muscle trace element concentrations differed between male and female walruses indicating either differences in habitat use or prey selection. Stable carbon and nitrogen isotopes were analyzed in liver and muscle and compared between males and females, as well as based on the Arctic sea ice minimum. Results indicated that male and female walruses differ in their isotopic niche. An increase in the days without sea ice caused a reduced stable isotopic niche area in males. Lower summer minimum ice area similarly reduced the isotopic niche among females, and the occupation of coastal haulouts caused a shift to lower trophic level prey. Fatty acids in muscle were highly variable compared to the fatty acids measured in blubber, and this variability appears to be driven by differences in fatty acid oxidation to support muscle activity. In blubber, reduced stratification between blubber layers coincided with lower percent lipid measurements and clear differences in fatty acid proportions were evident between males and females and among sample years. These studies indicate that adult walruses have adjusted their prey selection in response to climate-driven habitat changes. However, future research should assess foraging success in calves and juveniles as they may be more vulnerable to habitat change.