Relationships between a Fish Index of Biotic Integrity and Mean Length and Density of Brook Trout and Brown Trout in Wisconsin Streams

Abstract

Native brook trout Salvelinus fontinalis and introduced brown trout Salmo trutta support important recreational fisheries in Wisconsin, and coldwater index of biotic integrity (IBI) scores are often used to determine the quality of stream environments for these trout. To successfully manage biotic communities and fish populations, it is important to understand the relationships among metrics of interest. We quantified the relationships among the catch per linear meter (CPE) of brook trout and brown trout, their mean total lengths, and the coldwater fish IBI scores in second-order and third-order streams in Wisconsin. Brook trout CPE increased as coldwater IBI score increased, but there was no significant relationship between brown trout CPE and IBI score. The mean length of brown trout decreased as coldwater IBI score increased; the mean length of brook trout and IBI score were not significantly related. The mean lengths of both brook and brown trout decreased with increasing CPE. Balancing the management of trout density, length, and biotic integrity may be difficult in wadeable streams in Wisconsin. Our findings suggest that the increased abundance of brook trout is compatible with high IBI scores but that the increased abundance of brown trout and greater mean lengths are not.