Ecosystem studies of marine mammals and seabirds in Monterey Bay, California, 1996--1999

Ecosystem studies were conducted in Monterey Bay, California during the upwelling seasons of 1996–99 to determine the distribution, relative abundance, and community structure of marine birds and mammals relative to oceanographic, physiographic, and lower-trophic variables. Monthly surveys were conducted in conjunction with sampling of physical water characteristics and hydroacoustic zooplankton backscatter. Impacts of the strong El Niño 1997/98 and La Niña 1999 were investigated. Species occurrence varied throughout the study. Baleen whale densities were linked to the occurrence of euphausiids. Warm-water species of odontocetes were more abundant during El Niño, increasing overall diversity. Community structure of seabirds and marine mammals was explored using a unimodal ordination technique, Canonical Correspondence Analysis. Species separated along environmental gradients representing bathymetric depth and slope (Canonical axis 1), and within-season variables including mixed layer depth. Subtle differences in species-environment relationships were identified for the different oceanographic periods during this study.