Factors Influencing Density of Age‐0 Brown Trout and Brook Trout in the Au Sable River, Michigan

Abstract

The density of juvenile trout is influenced by many factors, including water temperature, discharge, substrate composition, and the presence of aquatic vegetation. The objective of this study was to determine habitat conditions that influence densities of age‐0 brown trout Salmo trutta and brook trout Salvelinus fontinalis in the Au Sable River, Michigan. Electrofishing was conducted with a 250‐V DC tote barge at 12 sites throughout the Au Sable River watershed from June through August of 2000 and 2001. Densities of age‐0 brown trout and brook trout varied significantly among sites located on the main stem as well as in tributaries. Analysis of covariance was used to evaluate annual interactions between age‐0 trout densities and habitat variables. Simple and forward stepwise linear regressions were used to model brown trout and brook trout densities in relation to habitat variables. Percent gravel substrate and percent emergent vegetation accounted for 62% of the variance in age‐0 brown trout density. In two separate analyses, mean minimum water temperature accounted for 31% of the variance in the density of age‐0 brook trout, whereas mean daily water temperature fluctuation accounted for 28% of the variance. Once habitat conditions that influence age‐0 fish production are identified, stocking programs should focus on areas where age‐0 fish would be able to survive. If no suitable juvenile habitat is available, managers should instead invest effort in enhancing or creating nursery habitat. Such efforts will not only be valuable to the growth and survival of stocked individuals but will also have the benefit of enhancing the potential for the fishery to be sustained through natural reproduction.