oikonos

INTER-ANNUAL VARIABILITY IN PATTERNS OF MARINE MAMMAL OCCURRENCE AND OCEAN CLIMATE OFF CENTRAL CALIFORNIA, 1986-1994, 1997-1999

C.A. Keiper1*, D.G. Ainley2, S.G. Allen3, J.T. Harvey4

1Oikonos, P.O. Box 979, Paradise Valley, Bolinas, CA 94924, USA; 2H.T. Harvey & Associates, 3150 Almaden Expressway, Suite 145, San Jose CA 95118, USA; 3Point Reyes National Seashore National Park Service, Point Reyes, CA 94956, USA; 4Moss Landing Marine Laboratories, 8272 Moss Landing Road, Moss Landing, CA 95039, USA

*E-mail address: carol@oikonos.org (C.A. Keiper)

ABSTRACT. The California Current System (CCS), a highly variable eastern boundary system, supports a rich marine mammal fauna. Variation of local coastal upwelling, coupled with larger scale processes (El Niño /La Niña affects the productivity and distribution of marine species at all trophic levels. Herein, we report 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, 1986-94 and 1997-99. Occurrence patterns were investigated using Geographical Information System, Percent Similarity 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, Phocoenoides dalli; harbor porpoise, Phocoena phocoena; and humpback whale, Megaptera novaeangliae) were related to bathymetry and changing ocean climate, likely mediated 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.

KEY WORDS: California Current System, bathymetry, cetaceans, coastal upwelling, El Niño, La Niña, marine mammals, ocean habitats, pinnipeds