Differences in Spawning and Emergence Phenology between Stocked and Wild Populations of Brown Trout in Southwestern Wisconsin Streams

Abstract

We compared the timing of spawning and emergence between stocked and wild populations of brown trout Salmo trutta in nine streams in southwestern Wisconsin during fall 1995 and spring 1996. Stocked populations of brown trout had a median date of redd formation 10 d before wild trout, 75% of redds being constructed 12 d before wild trout. On average, alevins of stocked trout emerged 17 d earlier from redds constructed on the median date of redd formation than did alevins of wild trout. Compared to wild trout, alevins of stocked trout emerged 13 d earlier from redds made on the date of 75% redd formation. Earlier fall spawning and the accompanying earlier spring emergence of alevins may influence reproductive success of the population. Timing of spawning should be carefully considered when selecting brown trout of wild or domestic origin to establish reproducing populations within streams.