An immunochemical approach to quantifying predation by euphausnds on the early stages of anchovy

Abstract

Off southern California (USA), euphausiid crustaceans appear to be significant predators on the early stages of northern anchovy Engrauljs mordax. Between 47 and 78 % of the natural mortality of northern anchovy eggs and yolk-sac larvae can be explained by euphausiid predation. The incidence of predation was determined from direct evidence provided by an immunochemical technique that detects anchovy remains in individual euphausiids. Rates of predation were determined from euphausiid feeding rates and digestion rates. The impact on the anchovy population was estimated by quantifying predator abundance by species, estimating predator and prey CO-occurrence considering the die1 migratory patterns of the predator, determining the number of prey removed d-', and generating natural mortality rates for the anchovy. Euphausiids ate 2.8 "/o of the anchovy population d-' in the nearshore area and 1.7 % d-' in the offshore area.