Paul E. Smith

Modeling the behavior of the northern anchovy, Engraulis mordax, as a schooling predator exploiting patchy prey

Abstract Extensive data sets on the bioenergetics of the northern anchovy, Engraulis mordax, and the patchy food distribution in its natural habitat allow its foraging dynamics to be inferred by modeling using techniques from population biology and behavioral ecology. The behavioral model consistently predicts that E. mordax grows much more slowly than would be expected with a pure, net-energy intake rate maximization strategy. The reduced growth rates could result from the fish avoiding zooplankton patches, where they are under increased predation risk, by swimming slowly in the waters between zooplankton patches. The combinations of growth rates and daily instantaneous mortality rates generated by the behavioral model are internally consistent with a Lefkovitch matrix population model, which includes an early juvenile stage of a stable and stationary population. Several novel and testable predictions are made by the behavioral model, including: (1) anchovies swim very slowly between zooplankton patch encounters; (2) within a patch fish swim very rapidly while searching for prey; and (3) fish often leave zooplankton patches before totally filling their stomachs. Given these encouraging initial results, the behavioral modeling approach appears to be a valuable technique for examining how potential habitat changes due to global warming may affect fish behavior and populations. Several such scenarios are proposed and discussed.

Acoustics in fisheries research--A perspective

Simple extension of existing fishery acoustics procedures will result in unnecessary delays in adding acoustical fishery survey data to the existing fishery management techniques. Progress in the coupled collection of amplitude - and frequency - domain acoustical data from fish aggregation promise useful advances in the utility of fishery acoustic studies. Fishery management problems are listed and transitions in the management of acoustics development, in the technology, and the biological studies are recommended.