Dan O'Keefe was fishing for salmon in the Pentwater River recently when he caught a foreign fish that has become a scourge in the Great Lakes and a harbinger of destructive changes.
O'Keefe landed a round goby, a menacing little fish that transoceanic freighters imported to the Great Lakes in ballast water in the late 1980s. The species, which is native to the Black and Caspian seas in eastern Europe, has harmed some native fish species and disrupted fishing at numerous sites around the lakes.
Having conquered the lakes, gobies are now extending their range to rivers and inland lakes across the region that flow into lakes Michigan, Superior, Huron, Erie and Ontario. Gobies have been spotted in rivers in all eight states around the Great Lakes, according to data compiled by the U.S. Geological Survey.
Several scientists said they aren't sure how goby invasions will affect fisheries in rivers and inland lakes. But they fear the worst.
"The presence of gobies doesn't mean the end of salmon or any other fish -- but it's something to be concerned about," said O'Keefe, a biologist and southwest Michigan district educator for the Michigan Sea Grant program. "Their effects could actually be worse in rivers than in lakes."
Gobies have been found in portions of all five Great Lakes. Researchers recently spotted the fish far upstream in several Michigan rivers, including the Grand, Muskegon, Pentwater, Jordan, Kalamazoo, Flint and Shiawassee.
The invader's colonization of inland lakes and rivers is significant because the bug-eyed fish competes with perch and other native species. The pugnacious imports eat the eggs of other fish species and are known to chase larger fish away from nesting sites.
The only benefit gobies provide is that they eat large quantities of zebra and quagga mussels -- up to 78 per day, per fish.
Experts have said the problems gobies cause far outweigh any benefits the invaders provide. Gobies multiply rapidly and suppress native fish populations; they've also been linked to an outbreak of avian botulism that has killed more than 70,000 fish-eating birds in the Great Lakes over the past decade.
The sheer number of gobies in some areas is staggering.
Researchers several years ago estimated there were 10 billion gobies in western Lake Erie. Gobies account for half of all fish in Muskegon Lake each spring, before migrating into Lake Michigan for the summer, according to scientists at Grand Valley State University's Annis Water Resources Institute.
David Jude, a University of Michigan research ecologist who discovered gobies in the Great Lakes, said he is concerned the invaders could disrupt some of Michigan's finest trout streams, including the Jordan River and Cedar Creek, a tributary of the Muskegon River.
Gobies have decimated populations of bottom-dwelling insects in parts of the Shiawassee River, in eastern Michigan, Jude said. Those insects, called benthos, provide food for many species of fish and other aquatic organisms. more