Final Technical Report: - Southwest Fisheries Science Center - NOAA

dependent. For example, the number of sightings peaked at an intermediate temperature
of approximately 17 degrees in the combined model (Fig. 18). Different functional forms
of the temperature variable were observed in each ecosystem because their temperature
range covered approximately half of the combined temperate range (Fig. 18). Ratios of
observed to predicted encounter rates were close to the expected value of 1.0 (range
1.012 to 0.987) for the individual and combined models in both ecosystems.
Figure 18. Encounter rate models built at a 60-km resolution for short-beaked common dolphin to explore
the effect of extent. The similarity of all models resulted in similar predictive power in both ecosystems.
Our assessment of extent suggests that the best predictive models are built using
ecosystem-specific data. For example, no predictive power was gained by using the
combined model for short-beaked common dolphins, but biased encounter rates were
obtained when the combined model for striped dolphins was used to predict distributions
in the CCE. Consequently, we used ecosystem-specific models in the spatial decision
support system. We will continue to pursue these analyses, however, because of their
potential to increase our understanding of species ecology. For example, the combined
model for striped dolphins showed a temperature threshold at 16 degrees, above which
encounters were relatively high and stable. This pattern was not observed in the models
60