724_Final Report.pdf - North Pacific Research Board

DFA and showed that there were changes in FA signatures among biopsies and therefore that they
reflected changes in diet, which was confirmed later in the QFASA model.
Model estimates were strongly influenced by the FA subset and CC set. The Reduced A and B
FA subsets were modified from the published Dietary FA subset and provided the best overall diet
estimates for spectacled and Steller’s eiders, respectively. The Extended Dietary subset and subsets
modified from it provided poorer diet estimates. FAs were omitted from the published subsets in order of
highest variability observed in CCs, which tended to provide better diet estimates. In contrast, Iverson et
al. (2007) removed FAs with large CCs, which produced poorer estimates in the model. However, diets,
CCs and bird species differed between studies and likely influenced model results. The Extended Dietary
subset includes all FAs in the Dietary subset and eight FAs that could be biosynthesized by consumers,
but whose levels in a consumer are also influenced by consumption of specific diet items. This may have
influenced the diet estimates because eiders were on a diet heavily influenced by carbohydrates from the
corn-based Mazuri (approximately 50% carbohydrate), which could have led to more biosynthesis of
these FAs than with diets contributing less carbohydrate. Although 27 subsets were evaluated, the
possibility remains for different combinations of FA to provide more accurate diet estimates and requires
further investigation.
Spectacled and Steller’s eider CCs were very similar to each other and generally shared similar
patterns to those of the common murre chicks CCs from Iverson et al. (2007). However, there were some
notable differences, which may be attributed to the differences in diet: common murres in Iverson et al.
(2007) were fed a piscivorous diet (100% Atlantic silverside) while eiders in this study were fed a more
terrestrial and high-carbohydrate diet (corn-based Mazuri) which could lead to more biosynthesis of FAs
in the eiders. Interestingly, the model provided similar diet estimates when using the Reduced A, B, and
Dietary subsets and eider CCs as estimates from using the Extended Dietary subset and common murre
CCs. We speculate that this may indicate that the Dietary subset and subsets modified from it are more
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