Invasive species Round Goby has population explosion in Great Lakes
Written by Muskegon Chronicle   
Tuesday, 03 February 2009 21:19

LUDINGTON -- A bug-eyed fish that snuck into the Great Lakes in the ballast tanks of ocean freighters two decades ago is now laying siege to Lake Michigan, according to new research data.

The round goby population enjoyed a population explosion in 2008. The invasive species accounted for nearly one-quarter of all prey fish in the lake last year, by weight, according to data compiled by the U.S. Geological Survey's Great Lakes Science Center.

"We're seeing a dramatic increase in gobies," said Chuck Madenjian, a research fishery biologist with the USGS. "Round gobies are now a substantial part of the total biomass of prey fish species ... we caught gobies in 300 feet of water."

The estimated volume of gobies in the lake ballooned to 10 million pounds in 2008, Madenjian said. By comparison, the total weight of all other prey fish species in the lake last year was estimated at 46 million pounds.

Gobies are thriving as populations of native prey fish species and alewife -- an invasive species that supports the artificial salmon fishery -- are decreasing.

The volume of all prey fish species, excluding gobies, dropped 34 percent last year, according to USGS data. Prey fish abundance in the lake hit another record low last year, for the second straight year, and was down 95 percent from the record high tallied in 1989.

Gobies are an undesirable species because they crowd out some native fish and eat their eggs. But some native fish species, especially smallmouth bass and walleye, feast on gobies.

Madenjian told a group of charter boat captains at a Michigan Sea Grant fisheries workshop in Ludington Saturday that lake trout and salmon may acquire an appetite for gobies.

Salmon imported to the Great Lakes in 1966 dine almost exclusively on alewife. The volume of alewives in the lake last year was down 30 percent from 2007, Madenjian said.

The bleak assessment of the lake's prey fish population prompted one angler at the fisheries workshop to ask: "Should we sell our fishing boats?"

Madenjian and other scientists at the meeting said there is no reason to panic over the lake's waning supply of prey fish.

"Is this the beginning of the end of the food chain in Lake Michigan? I don't think so," Madenjian said.

Some biologists believe gobies may become a major source of food for other fish in the lake, much in the way the alewife, another invasive species, supports the salmon fishery.

The Michigan Department of Natural Resources has slashed salmon stocking in the lake over the past decade to cope with the dwindling supply of alewives.

Scientists at Saturday's conference said salmon will likely eat goby if the fish are hungry enough.

Dan O'Keefe, an educator for the Michigan Sea Grant program, said he received a few reports last year of anglers finding dead gobies in the bellies of salmon they caught.

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