Reproductive interactions between sympatric brook and brown trout in a small Minnesota stream

The spawning seasons of Salvelinus fontinalis and Salmo trutta consistently overlapped by 2-4 weeks, during which time nearly 10% of all sexually active females were simultaneously courted by males of both species. Male brook trout attempted to hybridize most frequently; but these fish had little success. There was also strong evidence of frequent redd superimposition, particularly by the later spawning and larger brown trout. Analysis of redd site habitat demonstrated that these species had overlapping preferences. Although it seems likely that attempted hybridization and redd superimposition work to the disadvantage of both species, the effects of these activities are likely to be particularly severe for the brook trout, which spans earlier in the season, is smaller, and rarely survives to be old enough to spawn twice. Reproductive interactions may be partially responsible for the displacement of brook trout by brown trout in many regions of North America. -from Authors