INFLUENCE OF COVER ON THE SPATIAL-DISTRIBUTION OF LITTORAL-ZONE FISHES

Littoral-zone fish are thought to reduce predation pressure by seeking refuge within macrophyte beds or near the lake bottom, or by aggregat ing. We used underwater video to measure the spatial aggregation of pr ey fishes in the littoral habitat. At low density, fish were more aggr egated off the bottom in open habitats than when found off the bottom within macrophyte beds. At high densities, fish were primarily observe d near the lake bottom, and the presence or absence of macrophyte beds had little influence on spatial behavior. No difference could be dete cted in the degree of aggregation seen in fish on the lake bottom insi de or outside macrophyte beds. Our results lend field support to theor etical and laboratory research that suggests aggregative behavior in l ittoral-zone fish is strongly influenced by fish density and by habita t structure.