Thermal Habitat Partitioning by Fishes in Lake Michigan

Abstract

Thermal distribution of Lake Michigan fishes were determined by aimed bottom trawling (n = 68) along temperature isotherms (3–20 °C) in a region where the thermocline intersected the bottom off Grand Haven, Michigan, during September. Alewife (Alosa pseudoharengus), rainbow smelt (Osmerus mordax), spottail shiner (Notropis hudsonius), and trout-perch (Percopsis omiscomaycus) comprised 94% of the catch by numbers. Species segregated along temperature gradients. Patterns of thermal habitat partitioning were maintained despite rapid oscillations in thermocline location. Alewife, rainbow trout, and yellow perch (Perca flavescens) showed intraspecific differences in thermal distribution of size-classes. Thermal niche shifts of some fishes on the bottom apparently occur at dawn and dusk. Patterns of thermal resource use are considered in relation to competition, predation, and thermal ecology of the more common species.Key words: competition, fishes, habitat partitioning, Lake Michigan, predation, temperature