Complementarity in the Use of Food and Thermal Habitat by Lake Michigan Fishes

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Abstract
The potential for ecological segregation of Lake Michigan fishes was examined by comparing diets and thermal habitat use of common species. Samples were collected by bottom trawling (N = 68) off Grand Haven, Michigan, September 7–13, 1977. Five common species exhibited complementarity in the use of food and thermal habitat resources. During the day, adult alewife (Alosa pseudoharengus), and rainbow smelt (Osmerus mordax) had similar diets but occupied somewhat different thermal habitats. Young-of-the-year (YOY) alewives segregated from adult alewife and rainbow smelt on both habitat and food. Spottail shiner (Notropis hudsonius), YOY alewives, and yellow perch (Perca flavescens) used similar thermal habitats but fed on different prey. Trout-perch (Percopsis osmiscomaycus) tended to segregate from the others based on both food and thermal habitat but may experience diffuse competition. Adults of the three native species consume entirely different prey than exotic alewife and rainbow smelt. The native species which declined during the invasion of alewife and rainbow smelt were those with apparently similar habitat and food requirements to the exotics. These data suggest that competition is important in maintaining the structure of the Lake Michigan fish community.Key words: competition, fishes, food, habitat, Lake Michigan, predation, temperature