Final Technical Report: - Southwest Fisheries Science Center - NOAA

contour plot (Fig. 25). Inspection of the predicted 2005 species density maps overlaid
with survey sighting locations revealed that the models for Baird’s beaked whale also
failed to capture their distribution patterns (Fig. 25). We therefore re-examined the
models for both Risso’s dolphin and Baird’s beaked whale and found that there was only
one predictor included in each of the species’ models; the encounter rate and group size
models for Risso’s dolphin included distance to the 2,000 m isobath and slope,
respectively, while the encounter rate and group size models for Baird’s beaked whale
included depth and distance to the 2,000 m isobath, respectively.
Further inspection of the sighting plots suggested that the models for both species
might be improved using categorical variables to represent geographic regions rather than
the continuous variables included in the models. We therefore included static variables
as potential predictors in both the encounter rate and group size models to investigate
whether they would be more effective at capturing the two species’ distribution patterns.
For Risso’s dolphin, we used a categorical variable to represent the geographic strata
used to evaluate spatial predictive ability (see Section 3.5.1), although we combined the
three California offshore strata to increase sample sizes. For Baird’s beaked whale we
used a binary variable to indicate positions within or outside a 50 km distance from the
2,000 m isobath. Models for both species were substantially improved using the static
variables (see Section 4.8and Appendix A). The density contour plots for all other
species revealed that the 1991-2001 CCE models were effective at capturing the 2005
general distribution patterns, and were similar to plots generated by the final models that
were re-fit to the entire 1991-2005 dataset (Appendix A).
4.7.2 Eastern Tropical Pacific Models
When the initial ETP encounter rate and group size models (built using 1986-
2003 data) were used to predict population density across all surveys years (1986-2006),
the ratios of stratified line-transect to modeled density estimate (RD) ranged from 0.999 to
1.3 (Table 18). In general, the models captured the inter-annual variability in cetacean
distribution, as evident in the yearly contour plots of density predictions and cetacean
sightings (see Figures B-1a-o in appendix B). When the initial models were used to
predict on the novel year of data (2006), the RD values ranged from 0.668 for Cuvier’s
beaked whale to 5.602 for the blue whale, with most values between 1.1 and 2.5.
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