Spatial and Genetic Distribution of Brook Trout in Southeast Minnesota

Populations found at the edge of a species range are important in terms of range contraction, genetic divergence, and life history variants. Minnesota represents the western edge of the brook trout’s native range. Because of historically degraded stream conditions, previous stockings of eastern origin brook trout, and abundant brown trout populations, it was assumed that native brook trout were extirpated from southeast Minnesota.  Numerous stocking efforts have been aimed at maintaining or increasing their distribution.  Stocking records indicate at least eight genetic strains of brook trout have been stocked in southeastern Minnesota in the last 40 years. Our objectives were to examine these peripheral brook trout populations to determine their spatial and genetic distribution. Presence or absence of brook trout was determined from recent file data (<5 years) or electrofishing on 174 streams. Brook trout were present in 119 streams (68%).  Genetic data on 73 populations were analyzed to determine origin.  Several clusters of populations were not associated with known hatchery sources, but were primarily composed of geographic groupings from three main tributaries. Given their proximity to each other and that they do not conform to known hatchery stocks, 37 populations may have ancestry derived from remnant southeastern Minnesota populations.