Thesis (Ph.D.) University of Alaska Fairbanks, 2020An interdisciplinary approach is used in understanding change and resiliency in St. Lawrence Island (SLI) resources and resource users throughout this dissertation. Historically SLI inhabitants have relied on the Pacific walrus (Odobenus rosmarus divergens) for their survival and this resource is still highly valued for cultural and dietary purposes. The responses of Pacific walruses and SLI subsistence users to environmental change was analyzed. In walruses, reproductive capacity was analyzed using an anatomical approach as well as reproductive plasticity which was determined using a physiological approach to characterize their estrus cycle. A suite of anatomical measurements were developed to characterize reproductive capacity of walruses by analyzing ovaries from three distinct time frames during a 35-year period. Reproductive capacity was reduced during time frames when carrying capacity (K) was reached and when large environmental changes occurred in the Bering Sea, including years of very low sea ice extent. Reproductive capacity was high in times when K was lower and harvest levels were greater. Our results explained how perturbations in K and environmental changes may have influenced reproductive capacity of the population in the past. Endocrine techniques were used in ovarian tissues to determine if progesterone and total estrogens are useful indicators of female reproductive status in walruses harvested during the spring hunt. Progesterone and total estrogen concentrations were greater in the reproductive tissues of unbred and pregnant females than postpartum females, however neither hormone could distinguish between pregnant and unbred animals. These results provide the first physiological evidence for pseudopregnancy in this species, rather than a postpartum estrus. Lastly, discussions were held with SLI community members to determine changes in key subsistence resources and community resiliency with regard to food security. Walruses ranked highest among key resources. Stakeholders reported limited access and increased effort to hunt walruses, changes in crab abundance, and increases in commercially exploitable fish stocks. Changes were attributed to loss of sea ice, "bad" weather, and climate change. In order for SLI communities to continue their subsistence-based way of life, inhabitants may need to expand their diet to include less-preferred food items in place of harvested ice-associated species. In conclusion, loss of sea ice and rapid environmental changes in the Bering Sea have the potential to greatly impact walrus reproduction and the marine subsistence way of life that is practiced by SLI stakeholders.Cooperative Institute for Alaska Research, National Oceanic and Atmospheric Administration cooperative agreement NA13OAR4320056 with the University of Alaska, Rasmuson Fisheries Research Center, Resilience and Adaptation Program, the Erich Follman Memorial Student Research Support Scholarship, NSF's EPSCoR Internship, the Smithsonian, North Pacific Research Board Graduate Student Research Award, Coastal Marine Institute/Bureau of Ocean Energy Management and the Marine Mammal Commission (Grant #: MMC19-172)General introduction -- Chapter 1. Pacific walrus (Odobenus rosmarus divergens) reproductive capacity changes in three time frames during 1975-2010 -- Chapter 2. Endocrine profiling of reproductive status and evidence of pseudopregnancy in the Pacific walrus (Odobenus rosmarus divergens) -- Chapter 3. Life without ice: perceptions of environmental impacts on marine resources and subsistence users of St. Lawrence Island -- General conclusions -- References for general introduction and conclusion
