Marine mammal occurrence and ocean climate off central California, 1986 to 1994 and 1997 to 1999

Abstract

The California Current System (CCS), a highly variable eastern boundary system, sup- ports a rich marine mammal fauna. Variation in local coastal upwelling, coupled with larger scale processes (El Nino/La Nina) affects the productivity and distribution of marine species at all trophic levels. Herein, we present an analysis of the occurrence patterns of marine mammals in the central CCS and relate these patterns to changing ocean climate and prey availability. Data on marine mammal distributions, ocean conditions, and prey availability were collected in waters overlying the continental shelf and slope from Bodega to Monterey Bays, from 1986 to 1994 and 1997 to 1999. Occurrence patterns were investigated using geographical information system (GIS), percent simi- larity index (PSI), multiple logistic regression, and principal component analyses. Spatial patterns of the most frequently sighted species (California sea lion Zalophus californianus, northern fur seal Callorhinus ursinus, Pacific white-sided dolphin Lagenorhyncus obliquidens, Dall's porpoise Pho- coenoides dalli, harbor porpoise Phocoena phocoena,and humpback whale Megaptera novaean- gliae) were related to bathymetry and changing ocean climate, and were likely to have been medi- ated by changes in prey availability. Temporal changes were related to migration and significant differences in ocean structure resulting from both local and large-scale processes.