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Effects of prey abundance on distribution, density and territorial behavior of young rainbow trout in streams Slaney, Pat A.

Abstract

The object of this study was to test the hypothesis that prey abundance in large part regulates dispersion, territory size and aggressive behavior of young rainbow trout during the stream rearing phase of their life history. In laboratory test channels, where age 0+ fry were introduced into channels receiving three different amounts of prey and permitted to emigrate voluntarily, density of fry remained highest at the highest prey level. Also, the distribution of fry was positively associated with a gradient in prey abundance. Both territory size and frequency of aggressive encounter varied inversely with prey level; the higher the prey level, the smaller the territory and the lower the frequency of aggressive encounter. Emigration from the test channels was neither as rapid nor as marked when prey level was abruptly reduced, compared to when fry were initially introduced to the different prey levels. However, frequency of aggressive encounter significantly increased when the prey level was decreased and significantly decreased when the prey was increased. In Loon Outlet Creek, the abundance of prey was positively associated with summer fish biomass in one study section, while a positive association was not apparent for a second study section. The second, located closer to Loon Lake, on the average tended to have throughout the summer a higher fish biomass and higher prey density. In addition, the spring lakeward migration of juvenile rainbow trout was negatively correlated with prey density and positively correlated with temperature. It is suggested that in the natural stream habitat, the density of fry and juvenile rainbow trout is strongly influenced by prey density especially when associated with the metabolic effects of temperature and fish size.

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