Final Technical Report: - Southwest Fisheries Science Center - NOAA
Final Technical Report: - Southwest Fisheries Science Center - NOAA
Final Technical Report: - Southwest Fisheries Science Center - NOAA
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4.6.2 Seasonal Predictive Ability<br />
Results indicated that inter-annual variability in environmental parameters can<br />
explain part of the variation in the seasonal distribution patterns of some cetacean<br />
species, particularly for species with large numbers of sightings during the summer<br />
survey periods (Becker 2007). Seasonal geographic patterns in ranked species density<br />
were captured for three of the five species considered. Density plots for Dall’s porpoise<br />
(Fig. 24) illustrate a species for which summer models were effective at predicting the<br />
southward shift of animals during winter. However, the predictions for northern right<br />
whale dolphins demonstrate that extreme over-predictions can result in the areas off<br />
northern California where waters were cooler during winter than observed during the<br />
summer surveys (dark blue shading in Fig. 24B). Additional surveys are required to fully<br />
characterize environmental variability and improve predictive performance sufficiently to<br />
apply these models quantitatively. In particular, model input data must include the full<br />
range of conditions for the temporal/spatial period they are predicting, i.e. cold-water<br />
conditions during winter. If possible, future seasonal model development and evaluation<br />
should also include a broader range of cold-season oceanographic conditions to<br />
characterize inter-annual variation. A final complication is that some cetaceans found in<br />
the CCE during the warm season are migratory and nearly absent in the cold season. For<br />
these reasons, we did not make any predictions of cetacean densities in one season from<br />
data that were collected in another.<br />
4.7 Model Validation<br />
Data from the novel 2005 (CCE) and 2006 (ETP) SWFSC cetacean surveys were<br />
used to validate the final encounter rate and group size models constructed using data<br />
from 1991-2001 for the CCE and from 1986-2003 for the ETP. To assess the models’ fit<br />
to the validation data set and to examine the inter-annual variability in model predictions,<br />
density was predicted separately for each survey year. Methods used to evaluate model<br />
fit included visual inspection of geographic contour plots of the annual density<br />
predictions and computation of geographically stratified ratios of observed to predicted<br />
density.<br />
4.7.1 California Current Ecosystem Models<br />
When the CCE models built using 1991-2001 survey data were used to predict<br />
density across all survey years (1991-2005), density ratios (density calculated using<br />
standard line-transect methods divided by density predicted by the habitat model) ranged<br />
from 0.62 (Baird’s beaked whale) to 1.44 (northern right whale dolphin) (Table 18).<br />
Density ratios for the novel year (2005) predictions were more variable, ranging from<br />
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