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Defense Date


Document Type

Thesis - NSU Access Only

Degree Type

Master of Science

Degree Name

Marine Science

First Advisor

Amy Hirons

Second Advisor

Lori Polasek

Third Advisor

Verena Gill


Stable isotopes, vibrissae, Enhydra lutris kenyoni, northern sea otter, trophic dynamics, threatened, recovery


Stable isotope analysis, specifically of carbon and nitrogen isotopes, has been well documented as a tool for studying trophic ecology and understanding a population’s ecophysiology. Quantifying the δ13C in the tissue of an individual will indicate the carbon source in that individual’s diet, while quantifying the δ15N indicates the trophic position of that individual’s prey. Stable isotope values in northern sea otter (Enhydra lutris kenyoni) vibrissae from Alaska provided insight into annual trophic patterns of the increasing southcentral (SC) and southeast (SE) population stocks and the threatened southwest (SW) stock over a 20-year period (1994-2014). Values for δ15N did not significantly vary between the increasing SC and SE stocks. However, the values for these stocks varied significantly from the declining SW stock. Carbon stable isotope ratios did not vary significantly among all 3 stocks. Values for δ15N or δ13C did not significantly vary between sexes. Our results suggest that sea otters in the threatened SW stock are foraging at different trophic levels when compared to sea otters in the increasing SC and SE stocks. Our data also indicates there is a relationship between δ15N values and the Pacific Decadal Oscillation of the region. This information provides a valuable baseline of isotopic data that can be compared with data from past and future sampling efforts to monitor these populations and the implications of their trophic shifts.


Samples were collected under MMPA permit No. MA041309-5 issued to Gill in the U.S. Fish and Wildlife’s Marine Mammals Management office. Funding for this research was provided by the US Fish and Wildlife Service Section 6 funds awarded via Alaska Department of Fish and Game, through Cooperative Agreement #20-076. Stable isotope analyses were provided by C. France at the Smithsonian Museum Support Center. A special thank you goes to my incredible family and friends who have provided me with unconditional support throughout all of the ups and downs this experience has provided.

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