MODELING FORAGING IN THE NORTHERN ANCHOVY (ENGRAULIS-MORDAX) - INDIVIDUAL BEHAVIOR CAN PREDICT SCHOOL DYNAMICS AND POPULATION BIOLOGY

Many economically important oceanic fishes travel in large schools, bu t the foraging behaviors of these schools and the life history consequ ences of these behaviors have rarely been addressed. The availability of extensive information on bioenergetics of the northern anchovy (Eng raulis mordax) allows us to use this species as a case study. We model ed two types of potential behavior that fish could use to exploit a pa tchy environment: (i) maximizing growth rate or (ii) maximizing surviv orship to adulthood and reproduction, which is a function of both grow th and avoiding predation. Patterns from existing data sets on gut con tents and growth rates from the field for juvenile E. mordax were cons istent only with the prediction of maximizing survivorship. The model makes further testable predictions about (i) expected swimming velocit ies between zooplankton patches, (ii) patterns of size segregation in the formation of schools, (iii) the proportion of zooplankton patches that schools consume, and (iv) reactions to decreases in environmental quality. Overall, the model predicts that anchovies spend at least 25 % of their time in schools that are too large to be energetically econ omical and suggests further research on several variables that could a ffect populations of schooling fishes.