Lake whitefish and walleye population responses to dreissenid mussel invasion in eastern Lake Ontario

We reviewed responses associated with the invasion of dreissenid mussels by two eastern Lake Ontario fish populations and the fisheries they support. Resurging lake whitefish and walleye populations declined following dreissenid mussel invasion in the early 1990s. Impacts on whitefish were associated with the loss of a key diet item, Diporeia, and its replacement with diet items of lower energy value. Impacts featured a die-off, dispersal, declines in juvenile and adult condition and growth rates, delayed age-at-maturity, and several years of reproductive failure. Impacts on walleye were consistent with dreissenid driven ecosystem change, particularly, clearer water. The key response by the walleye population was a downward shift in recruitment levels. This shift appears to be due to a change in the stock-recruitment relationship caused by decreased survival during early life (i.e. egg to 4-months), and suggests that the carrying capacity for these early life stages has diminished. Currently, whitefish re...