724_Final Report.pdf - North Pacific Research Board

observed in CCs (e.g., Nordstrom et al. 2008). Twenty-seven subsets of the 72 FAs identified were tested
in our model optimization exercise (see Appendix 1). Relative proportions of individual FA in each new
subset were normalized to a sum of 100%. Subsets were used in the QFASA model and performance was
evaluated using all biopsies and all diets from all eiders. The FA subset that provided the lowest overall
sum of the squared errors (SSE) of diet was determined to be the optimal subset for our QFASA model,
where SSE = (actual proportion of diet item – model estimate of diet item) 2 summed across all diet items
for Diet 1, 2, and 3.
QFASA model
To evaluate the reliability with which diet items could be distinguished in the model, we first performed a
number of simulations using the captive eider diet database. These simulations were performed without
CCs to assess the ability to estimate diet composition based only on differentiating and quantifying diet
items by their FA signatures (sensu Iverson et al. 2004). We constructed five pseudo diets: Diets 1-3 were
based on the actual Diets 1-3 that the eiders consumed. Diet 4 represented a marine diet without the
commercially processed Mazuri. Diet 5 represented a diet comprised of only bivalves, which are the
primary diet item for spectacled eiders wintering in the Bering Sea (Lovvorn et al. 2003). Simulations
were used to evaluate how the accuracy of our estimates was affected by diets and FA subsets.
Simulations were performed 1000 times for each constructed diet. Prey-on-prey simulations were also
performed to determine how well each individual diet item could be differentiated as itself from all other
diet items in the diet library. These were done by taking each diet item in the library and dividing the
samples into two sets: a modeling set and a simulation set. The selected diet item was modeled with the
modeling set and all other diet items in the prey library. The simulation was performed 1000 times for
each diet item. Details of the simulation procedures are provided in Appendix B in Iverson et al. (2004).
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