Influence of Cover on the Spatial Distribution of Littoral-zone Fishes

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Abstract
Littoral-zone fish are thought to reduce predation pressure by seeking refuge within macrophyte beds or near the lake bottom, or by aggregating. We used underwater video to measure the spatial aggregation of prey fishes in the littoral habitat. At low density, fish were more aggregated off the bottom in open habitats than when found off the bottom within macrophyte beds. At high densities, fish were primarily observed near the lake bottom, and the presence or absence of macrophyte beds had little influence on spatial behavior. No difference could be detected in the degree of aggregation seen in fish on the lake bottom inside or outside macrophyte beds. Our results lend field support to theoretical and laboratory research that suggests aggregative behavior in littoral-zone fish is strongly influenced by fish density and by habitat structure.