ECOLOGY AND DISTRIBUTION OF THE NORTHERN SUBPOPULATION OF NORTHERN ANCHOVY (ENGRAULIS MORDAX) OFF THE US WEST COAST

Northern anchovy (Engraulis mordax) are a dominant fish in the northern California Current and are important prey for many predators. However, little is known about how anchovy distribution and abundance are affected by oceanographic variability in the eastern Pacific Ocean. We examined the relationship between anchovy abundance and environmental variables at two spatial and temporal scales: mesoscale (surface temperature, salinity, density, chlorophyll a, distance from shore, and depth) and macroscale (Pacific Decadal Oscillation Index, Multivariate El Nino-Southern Oscillation Index, timing of the spring transition to upwelling conditions, and abundance of cold-water zooplankton). Anchovy densities increased significantly from 1999-2004, and decreased significantly from 2005-06 in conjunction with delayed coastal upwelling and decreases in the overall abundance of cold- water zooplankton. Sea surface temperatures and proximity to the shore explained most anchovy abundance and distribution variations. When lagged by one year, a northern copepod biomass anomaly strongly correlated to age-1 anchovy survival, suggesting that copepod abundance may determine year-class strength.