Rainbow Smelt Decimate Walleye Stocks
Data now confirm that walleye stocks plummet after rainbow smelt move into a lake. Rainbow smelt arrived in the Great Lakes during the 1920s, and have since spread to the Hudson Bay and Mississippi watersheds. By 1968 they were in several of Wisconsin's inland lakes. The invasive fish are blamed for eliminating yellow perch and cisco from some lakes.
Scientists at the University of Wisconsin in Madison have produced evidence showing that rainbow smelt also decimate walleye populations. In northern Wisconsin lakes with smelt, young walleye are far less prevalent. Counts of young-of-year fish per kilometre of shoreline found an average of 26 walleye in natural populations of smelt-free lakes, versus only seven walleye in smelt-infested lakes.
During the first five years after rainbow smelt arrived at a lake, walleye populations didn't suffer. Subsequently though, the decline was dramatic. Depending upon the lake, walleye numbers dropped by 50 to 90 percent.
How rainbow smelt harm walleye isn't entirely clear. The invasive species could be both preying on walleye fry and competing with them for zooplankton.
So far, rainbow smelt have gotten into at least 26 Wisconsin lakes. Hundreds more lakes in the state that support walleye fisheries are at risk if the smelts continue to spread.
Norman Mercado-Silva, Greg G. Sass, Brian M. Roth, Stephen Gilbert and M. Jake Vander Zanden. 2007. Impact of rainbow smelt (Osmerus mordax) invasion on walleye (Sander vitreus) recruitment in Wisconsin lakes. Canadian Journal of Fisheries and Aquatic Sciences. 64(11): 1543-1550.