Spawning Habitat Selection by Rainbow Trout in the Pere Marquette River, Michigan

We evaluated habitat features (i.e., substrate particle size, water depth, water velocity) at spawning redds and randomly selected reference locations (where spawning activity was not apparent) to determine importance of these features to rainbow trout (Oncorhynchus mykiss) spawning habitat use in the Pere Marquette River, Michigan, 1997 to 1999. Rainbow trout selected areas with small gravel, large gravel, and small cobble substrates for redd construction over areas with clay, silt, sand, and large cobble. Rainbow trout redds were located in areas where the stream velocity was significantly higher (F = 97.77, df = 630, p < 0.0001) than velocities that were recorded at reference sites, and redds were located in water that was significantly shallower than what was typically found in the study reaches (F = 113.84, df = 629, p < 0.0001). Water temperature did not affect selection of redd locations. Because rainbow trout spawn during spring in Michigan when water temperatures are cool, within-reach variation in water temperature may have minimal influence on choice of locations for redd construction. These microhabitat data provide an indication of rainbow trout spawning habitat utilization, and can be used to identify critical habitats that may serve as rainbow trout spawning sites, and provide guidance on targets for habitat improvement projects in the Pere Marquette River and elsewhere. INDEX WORDS: Rainbow trout, spawning habitat selection, Pere Marquette River.