Stock structure of rainbow smelt in western lake superior: Population characteristics

Significant differences in length-frequency distributions, fecundity, and growth of rainbow smelt Osmerus mordax were found among collections from three zones along the Minnesota shoreline of Lake Superior. These differences were consistent with genetic evidence suggesting three discrete stocks of rainbow smelt. Geographic separation, possibly in combination with predation, may have been responsible for the isolation of stocks to the extent that local adaptations resulted in the observed differences. Although statistically significant, the actual differences in traditional population characters appeared small, potentially a result of weak or recently applied selective pressures. Future changes in predatory or competitive pressures or changes in exploitation rates may alter selective pressures and thus may have important influences on dynamics and condition of rainbow smelt stocks in Lake Superior.