RELATIVE IMPORTANCE OF TEMPERATURE, FOOD, AND PHYSICAL STRUCTURE TO HABITAT CHOICE BY SMALLMOUTH BASS IN LABORATORY EXPERIMENTS

Previous field studies suggest that the preference for an optimal temp erature is often overridden by a stronger preference for other habitat variables such as physical structure. I used a temperature gradient t ank with various treatments of ration, prey availability, and cover to test the relative importance of these factors in conjunction with tem perature on habitat selection by individual smallmouth bass Micropteru s dolomieu. The presence of food and cover (presented in separate expe riments) significantly affected the temperature selected by smallmouth bass. Fish presented with a limited amount of food at a position of g reater than preferred temperature in the tank increased the time spent at high temperatures, whereas fish allowed to feed till satiated retr eated to the cold end of the tank for most of the day. When covet was present at the warm end of the tank, the mean time spent in this area was five times greater than when no cover was present in the tank. The preference for cover at high temperatures contradicts expectations ba sed solely on bioenergetic considerations. However, the reduced activi ty of fish using cover at higher temperatures suggests that the increa sed metabolic costs incurred during exposure to high temperature can b e offset by decreased activity costs. These results suggest that even when temperature is not a primary consideration in habitat selection, its effects are often mediated through other behavioral responses.