Right now the alewives are not in good shape. Alewives, herring-like fish, are not native to the Great Lakes. The small, silvery fish were introduced in the late 1800s and overwhelmed native fish, such as yellow perch and walleye. In recent years, an increase in predator fish has reduced the amount of alewives, which play a critical role in the food chain that supports sport fish such as chinook salmon. Although scientists can't pin down the cause of the alewives' deterioration, they suspect it is tied to an improvement in water quality that has reduced the amount of nutrients in the lake.
Many alewives appear stressed and weak.
Normally, if the population of alewives declined due to predators, the remaining fish would fare well because there would be less competition for food. The total weight, or biomass, of alewives in Lake Ontario has fallen by one-third since a peak in the late 1970s, Abraham said. Also, the biomass of smelt, a popular prey for predator fish, has dropped to an all-time low, he said. The survival rate for young alewives is lower than expected. Many fail to reach adulthood.