Evaluating Seasonal vs. Spatial Extrapolation for Cetacean Distribution Models in the California Current

Abstract

Species distribution models (SDMs) have been developed for multiple cetacean species within the California Current Ecosystem (CCE) from shipboard survey data collected by the Southwest Fisheries Science Center (SWFSC) in summer and fall, thus limiting the ability to inform management decisions in cool seasons when abundance and distribution patterns are substantially different. Winter and spring SDMs have been developed for a few species using California Cooperative Oceanic Fisheries Investigations (CalCOFI) shipboard survey data, but model predictions are limited to the waters off southern and central California. In this study, winter and spring density estimates for the entire CCE study area were made from SWFSC summer and fall model predictions (temporal extrapolation) and CalCOFI winter and spring model predictions (spatial extrapolation) for short-beaked common dolphin (Delphinus delphis delphis), Pacific white-sided dolphin (Lagenorhynchus obliquidens), Dall's porpoise (Phocoenoides dalli), and fin whale (Balaenoptera physalus). The performance of the models was compared based on available abundance estimates and documented distribution patterns in the cool seasons. Results reveal species-specific ecological factors to consider when extrapolating model predictions temporally or spatially, including whether a given study area includes a species “core habitat”, and whether static variables should be included when a species exhibits temporal distribution shifts.