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, but the foraging behaviors of these schools and the life history consequences of these behaviors have rarely been addressed. The availability of extensive information on bioenergetics of the northern anchovy ( Engraulis mordax) allows us to use this species as a case study. We modeled two types of potential behavior that fish could use to exploit a patchy environment: ( i) maximizing growth rate or (ii) maximizing survivorship to adulthood and reproduction, which is a function of both growth and avoiding predation. Patterns from existing data sets on gut contents and growth rates from the field for juvenile E. mordax were consistent only with the prediction of maximizing survivorship. The model makes further testable predictions about ( i) expected swimming velocities 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 economical and suggests further research on severa l variables that could affect populations of schooling fishes. Resume : De nombreaux poissons d'importance commerciale se deplacent en grands bancs, mais le comportement de recherche de nourriture de ces bancs et les consequences de ce comportement sur le cycle vital ont rarement ete etudies. La