AMERICAN anglers are up in arms following the discovery that the humble ruffe has invaded the massive Lake Michigan.
The ruffe turned up during a routine survey of the water by the US Fish and Wildlife Service (USFWS) – the first confirmed finding of the species there.
Ruffe were first discovered in the Duluth Harbour, Minnesota and in the St Louis River estuary of Lake Superior in 1986.
Since then their numbers have rocketed and their range has expanded into the Wisconsin, Michigan and Ontario waters of western Lake Superior, and to one location in Michigan waters of Lake Huron.
Control measures have slowed range expansion since 1995, but this recent invasion in Lake Michigan indicates that ruffe are continuing to expand in the Great Lakes.
“Although the effects ruffe will have on native Great Lakes fish populations are difficult to predict,” said Mark Dryer, project leader for the USFWS Ashland, Wisconsin fishery resources office. “Strong evidence suggests they compete with native fish for food and space.”
In the Duluth Harbour where ruffe have become a dominate species, native species like yellow perch and some bait fish have declined markedly. And the problem is that unlike the native perch species, ruffe have no known economic, recreational or environmental value to US anglers.
Biologists are uncertain about how the fish moved into Lake Michigan. It is possible that the fish migrated from another location, but the USFWS believes it is more likely the fish was transported in the ballast water of a commercial ship.
Ballast water exchange is believed responsible for the initial movement of ruffe from their native habitat in Europe to the Duluth Harbour. When a ship takes on ballast water to stabilize a cargo load, aquatic species can be drawn into the tanks and survive until they are released into a new area.
“It would be helpful to know how these fish got here so we can expand measures to stop future movement,” said USFWS regional director Bill Hartwig. “But, the more immediate issue is what we do about the ruffe now that they are here. If they move into southern Lake Michigan, it is possible they could enter the Mississippi River ecosystem through the Chicago Canal system.”