Anchovy foraging: simulating spatial and temporal match/mismatches with zooplankton

Prey abundance is only a useful correlate of fish growth rate if it is cons idered within a match/mismatch hypothesis framework. We developed a model t o explore the extent to which the growth rates of juvenile anchovies (Engra ulis capensis) are influenced by temporal and spatial match/mismatches with the copepod Calanoides carinatus, a major component of their diet. The dis tributions of copepods and anchovies are dynamic, so that predation by anch ovy may dramatically impact on its prey's spatial distribution. Predation r ates by resident fish were commensurate with the average and maximum specif ic copepod production rates at fish densities of approximately 1 and 3.5 t. km(-2), respectively. The spatial arrangement of fish biomass and the tempo ral overlap between fish and copepod abundances substantially modified both anchovy and copepod growth estimates. Predicted optimal shoal sizes sugges t that additional factors such as predator avoidance or the energetics of m aintaining school structure may be important. The model emulated observed v ariability in anchovy growth rates and confirmed the prediction that the av ailability of high-sustained abundances of food along the West Coast may be a critical "bottleneck" contributing to the strength of recruitment to the South African pelagic purse-seine fishery.