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Final Technical Report: - Southwest Fisheries Science Center - NOAA

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Figure 21. Predicted average density (AveDens), standard error (SE(Dens)), and upper and lower<br />

lognormal 90% confidence limits (Lo90% and Hi90%) based on models for: (A) short-beaked common<br />

dolphin and (B) Dall’s porpoise.<br />

4.5 Inclusion of Prey Indices in Habitat Models<br />

We used daily transects as our unit of analysis to explore whether the inclusion of<br />

mid-trophic species data improves the fit and predictive power of cetacean-habitat<br />

models. The use of daily transects increased the number of segments containing a<br />

sighting, but results in segments of different lengths. Our analysis of the effect of scale<br />

on cetacean-habitat models in the ETP suggests that segment lengths from 2 to 120 km<br />

occur within a single domain of scale. Consequently, segments of varying lengths should<br />

not impact model results for the ETP. Analyses for the CCE, however, were not<br />

conclusive. Therefore, to help standardize the length of the segments, we used only days<br />

on which a minimum distance of 60 km was travelled on effort.<br />

Sample sizes were large enough to model striped dolphins and short-beaked<br />

common dolphins in both the ETP and CCE. We also modeled a species unique to each<br />

63

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