Blubber fatty acid signature analysis of harbor seals in Alaska, 1997-2010.
The projected course and rate of global climate change presents major challenges to the wellbeing and survival of Arctic and subarctic marine mammals. In Alaska, the harbor seals (Phoca vitulina richardii) broad range and severe population decline within certain regions led to increased research efforts to investigate the potential influence of diet changes on their lack of recovery. While these studies provide the foundation of knowledge regarding Alaskan harbor seal foraging ecology, detailed temporal and spatial changes in the harbor seals diet and possible impacts of diet overlap with other Alaskan pinnipeds has yet to be investigated. To date, the majority of harbor seal diet studies have used traditional diet determination methods. Due to the inherent limitations and sampling biases associated with these traditional techniques, blubber fatty acid (FA) analysis has emerged as one of the best methods of investigating diet in marine mammals. The goal of this dissertation was to characterize blubber FAs of Alaskan harbor seals through the evaluation of 15-years of blubber FA signatures. To gain an understanding of spatial and temporal differences, harbor seal blubber FA profiles were qualitatively investigated for regional, seasonal, and age class differences. In addition, to examine possible prey resource partitioning between different species populations, we compared regional and seasonal FA profiles of harbor seals and Steller sea lions within Prince William Sound and Southeast, Alaska. Lastly, differences between harbor seal reproductive state (pregnant, lactating, non-lactating-non-pregnant females), mother-pup pairs, and pinniped families were investigated to explore harbor seal blubber FA distribution during lactation. Key findings demonstrate the large degree of diet variability among harbor seal stocks within Alaska and shed light on how diet differences among Alaskan pinniped populations, and the physiological and behavioral limitations of the harbor seal lactation strategy, may be impairing population recovery in certain areas. As a sentinel species in Alaska, the ability to survey blubber FAs of harbor seals provides a way to not only monitor diet changes that could lead to population level impacts, but also provides a means to oversee prey community changes and ecosystem health within the regions they inhabit.