Invaders take Big Lake food from game fish
Written by Muskegon Chronicle   
Sunday, 22 April 2007 18:27

The volume of prey fish in Lake Michigan -- the food supply for big sport fish -- plunged last year to the lowest level ever recorded, while foreign invader mussels and the troublesome goby enjoyed population explosions, according to the latest government data.

Scientists familiar with the data said the findings do not spell doom for Lake Michigan's thriving salmon fishery. But they warned that the near-record salmon catches of the past two years likely won't last much longer.

"We're in the midst of some major ecological changes in the Great Lakes," said David Jude, a research scientist at the University of Michigan.

Scientists from the U.S. Geological Survey's Great Lakes Science Center found 60 kilotons of prey fish in Lake Michigan during an annual survey conducted last fall. That was the lowest volume recorded since 1973, when the government began tracking the abundance of alewife, bloater, rainbow smelt, sculpin and stickleback in Lake Michigan.

The density of zebra and quagga mussels in the lake tripled last year, while the number of goby increased 16-fold between 2005 and 2006, according to government data. Similar downward trends among certain prey fish were recorded in all five Great Lakes, researchers said.

The new fish data is significant for two reasons: Prey fish support larger fish species coveted by anglers, including salmon, lake trout and steelhead; and the soaring numbers of zebra mussels, quagga mussels and goby means the exotic species are dominating a growing piece of Lake Michigan's biological pie.

Jude said mussels intercept vast quantities of fish food and other nutrients, leaving fish and other aquatic life scrounging for leftovers.

"The dreissenids (zebra and quagga mussels) filter out the energy and send it to a dead end, ecologically," Jude said. "Where before you had fish, now you have mussels."

There was some good news in the annual prey fish survey: The volume of slimy sculpin and ninespine stickleback in Lake Michigan increased in 2006 and the resurgent perch population remained strong, according to federal data.

But the overall picture is gloomy and casts a cloud of uncertainty over the future of the Lake Michigan sport fishery, said Jim Dexter, Lake Michigan basin coordinator for the Michigan Department of Natural Resources.

"The $64,000 question is, will the forage community (prey fish) hold up and continue to provide reasonable fishing in Lake Michigan and allow us to meet our objectives for maintaining native fish species," Dexter said. "There's a lot of angst out there."

Jude and other scientists familiar with the data said Lake Michigan's prey fish populations appear headed in the same direction as those in Lake Huron. Alewife began to vanish from Lake Huron in 2002 and the chinook salmon fishery collapsed the following year, after two years of near-record catches.

The chinook fishing on Lake Michigan has been phenomenal the past three years, despite the fact that the volume of adult alewife in the lake has been on a steady decline since 2002.

The four states around Lake Michigan reduced salmon stocking by 25 percent last year in a bid to bolster the shrinking alewife population.

Chuck Madenjian, a U.S. Geological Survey fishery biologist who worked on the study, said increased predation by salmon and lake trout are reducing the number of prey fish in the lake.

Jude said he believes prey fish are suffering because zebra and quagga mussels are consuming huge amounts of nutrients which otherwise would be eaten by tiny organisms that fish need for sustenance.

Under the worst-case scenario, Lake Michigan's alewife population would crash and the salmon fishery would follow suit.

Dexter said he believes the salmon fishing in Lake Michigan will be outstanding again this year because there are large numbers of juvenile alewife in the lake. The annual trawl survey in Lake Michigan does not track juvenile alewife, only adults.

Despite the presence of many juvenile alewife in the lake, Dexter said the lake's sport fishery is in a "precarious" state due to the soaring number of zebra and quagga mussels covering the lake bottom. "There is cause for concern," Dexter said.

Zebra mussels have caused profound ecological changes and billions of dollars in damage since arriving in the Great Lakes in 1988, according to scientific studies. The mussels have triggered toxic algae blooms, decimated populations of tiny shrimp that fish eat and coated miles of Great Lakes shorelines with mats of dead, stinky algae laced with potentially deadly bacteria.

Quagga mussels are the larger, tougher cousin of zebra mussels. Quaggas, which are capable of living in the deepest parts of Lake Michigan, are overwhelming zebra mussels and colonizing vast areas of the lake bottom, researchers said.

Goby, which compete with perch and are now abundant in places like the Muskegon and Grand Haven channels to Lake Michigan, are spreading across the lake, said Chuck Madenjian, a USGS research fishery biologist.

Despite the decline of prey fish and the spread of exotic mussels and goby, Madenjian said "the sky is not falling" on Lake Michigan's sport fishery.

"It's not a clear-cut panic situation yet," Madenjian said.
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