Factors Influencing the Size Structure of Brook Trout and Brown Trout in Southeastern Wyoming Mountain Streams

We used discriminant models to identify relations among size structures of stocks of brook trout Salvelinus fontinalis and brown trout Salmo trutta and features of their habitats in small mountain streams (2,377-2,975 m above mean sea level) in the Medicine Bow National Forest, Wyoming. Size structure was predicted from position of the study reach in the watershed, from channel gradient, and from composition of the salmonid community. Brook trout were predominantly small in high-elevation, moderate-gradient, forested reaches with allopatric populations; they were larger in mid-elevation, low-gradient, meadow reaches that contained some brown trout. Brown trout were mostly small in mid-elevation, moderate-gradient, forested reaches; however, more large brown trout occurred lower in the watersheds, in meadow or rangeland stream reaches that had low gradients and that supported allopatric populations.