724_Final Report.pdf - North Pacific Research Board

Abstract
Fatty acid (FA) signature analysis has been used to study trophic relationships and foraging ecology in
marine ecosystems. This powerful method provides information about diets over a longer period of time
(e.g., 2-4 weeks) rather than just the most recent meal. Using a comprehensive database of diet FA
signatures and accounting for consumer FA metabolism, it is possible to estimate the proportions of diet
items in the consumer diet using quantitative FA signature analysis (QFASA). However, before applying
QFASA to free ranging populations, ideally, a captive study is performed to assess the quantitative
characteristics of the study species’ FA metabolism. We conducted feeding experiments to validate the
use of QFASA in captive spectacled (N=8) and Steller’s eiders (N=8) as a minimally invasive method for
studying the diets of these threatened birds. From the long-term feeding period, we assessed the
quantitative characteristics of FA deposition and developed calibration coefficients (CCs) for individual
FAs to account for eider lipid metabolism. We then tested the model and CCs by estimating the diets of
the captive eiders. Our results revealed that QFASA accurately indicates diet and diet switches in captive
eiders for these diet items. QFASA also confirmed that complete FA turnover of the new introduced diets
was not complete by 21 or 29 days, and that diets could be estimated over an extended period of > 29
days. Thus, our understanding of diet can be backtracked to more than a month in feeding eiders. We
conclude that applying QFASA techniques to eiders in the wild has the potential to provide valuable
information about their diets at different life history stages.
Key Words: fatty acids, diet, foraging ecology, Somateria fischeri, Polysticta stelleri
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