Genetic versus demographic stock structure of rainbow smelt in a large fragmented lake

Abstract Identification of fish stocks plays an important role in fisheries management, but stock identification often depends on the techniques used and the management goals as much as on actual population structure. Historically, stocks were identified by place of capture, population demography and morphology, but genetic stock identification has become a standard approach. Here, we evaluate the stock structure of rainbow smelt (Osmerus mordax) in three basins of Lake Champlain separated by causeways using genotype data from six microsatellite loci and 26 years of demographic data. No genetic differences among rainbow smelt from the different basins were evident, which suggests that gene flow occurs among basins. However, length, age, and catch-per-unit-effort of rainbow smelt suggests asynchronous population dynamics in the different basins, and thus each basin may hold populations that are at least partially isolated from one another. Consequently, we conclude that while rainbow smelt in Lake Champlain consist of at least three demographic stocks they may form only a single genetic stock. Our results concur with other studies that suggest care should be taken when only a single method of stock identification is used.