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Great Lakes Article:

Michigan fishing industry is threatened by quickly disappearing 'shrimp'
Gannett News Service
01/02/04

DETROIT -- One of the principal food sources for whitefish is disappearing rapidly in the Great Lakes, a change that threatens to shake up the food chain and hamper Michigan's large commercial fishing industry.

Diporeia, a half-inch-long, shrimp-like creature that lives on the bottom of the Great Lakes, has been wiped out in portions of Lake Erie, Lake Michigan, Saginaw Bay and Lake Ontario. About 17,000 square miles in the Great Lakes no longer have diporeia.

''We have never seen anything like this,'' said Tom Nalepa, the main research biologist studying the decline in diporeia population. He works in Ann Arbor at the Great Lakes Environmental Research Laboratory.

Research biologists found densities of diporeia in the 1980s between 10,000 to 20,000 per square mile of sediment in parts of the Great Lakes. Now in many of the same spots, no diporeia are found, Nalepa said.

Diporeia, sometimes re-ferred to as a fresh-water shrimp, is a main food source for many fish in the Great Lakes. Fish that don't eat diporeia eat fish that do.

Whitefish have become one of the first casualties of the loss of diporeia, re-searchers say.

Slimming down

Some of the fish caught now are much smaller than in the past, Nalepa said. Studies on their stomachs have found the fish have been feeding on zebra mussels and another invasive species known as quagga mussels, which are not as healthy for the fish as fat-enriched diporeia.

''The shells (from the mussels) pack their stomachs and they think that they are full,'' Nalepa said. ''They are getting skinnier and skinnier. The shell has no nutritional value at all.''

In the past, whitefish could be found that were 2 feet long and 5 pounds, said Jim Johnson, a research biologist for the state Department of Natural Resources. Now whitefish range from 20 to 22 inches. Some can't be used as filets because they are too thin, he said.

''We are concerned on how this is going to affect the future of the commercial fishing industry,'' Johnson said.

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