The study says the number of adult alewives in Lake Michigan fell 70 percent between the fall of 2003 and the fall of 2004. The level is about five percent of what it was when chinook salmon began to be stocked in the Great Lakes in the mid-1960s.

On Lake Huron, the alewife population is essentially zero.

Biologists believe the growing number of chinook in the lakes have gobbled up the fish. Alewives may also have been hit by invading species and the cold weather.

Biologist Paul Peeters with Wisconsin's Department of Natural Resources says fisheries experts are now considering stocking the lakes with fewer salmon, despite the economic benefits salmon bring.