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Great Lakes Article:

UVM research documents
fish eating zebra mussels

By LISA RATHKE

Article Courtesy of the Associated Press

August 16, 2001

ABOARD THE MELOSIRA, Vermont (AP) -- University of Vermont researchers have discovered that fish are feeding on zebra mussels in Lake Champlain and are investigating whether that diet could reduce the population of the nuisance species that has infested lakes across the country.

" We don' t believe that they' re going to get rid of zebra mussels by any stretch but if they can make a dent that would be pretty incredible in itself, " said Mary Watzin, head of the University of Vermont' s Rubenstein Ecosystem Science Laboratory.

With an underwater, remote-controlled video camera, Watzin and her team of researchers have filmed sheepshead and other fish eating zebra mussels off a sunken railroad barge near Port Henry, N.Y. The barge is scattered with broken mussel shells.

" The sheepshead fish in Lake Champlain seem to be learning that zebra mussels are food, " she said from the deck of the Melosira, the university' s research boat.

Sheepshead, also known as freshwater drum, apparently crush the mussels with their jaws and spit out the shells, she said. Other fish, such as yellow perch and pumpkinseed, feed on the smaller, younger zebra mussels, digesting them whole or spitting out the thinner shells.

Zebra mussels, native to Europe, have infested freshwater lakes and rivers from the Mississippi River east. They can choke out native species, clog water filtration systems and sewage plants, and create hazards to swimmers and boaters.

This week, Watzin spent three days on the Melosira to gather more evidence.

She filmed fish pecking at the mussels and spitting out the shells. The crew set out gill and trap nets at night to catch fish to take back to the lab. There they will analyze their contents to see how much of their diet is zebra mussels and how that could affect their health.

By the second of the three days, they hadn' t seen or caught any sheepshead. Plenty of sunfish, however, hovered over the barge, and ingested smaller mussels, while the remote controlled camera, which Watzin operates with joy sticks from the boat, watched. The gritty image of a school of fish floating over beds of crushed shells played above board on a monitor.

The research is funded by a $50, 000 grant from the Argosy Foundation.

Watzin said she doesn' t think the fish will control the mussels but their feeding behavior could help reduce the zebra mussel population.

" One of the really interesting things when you see zebra mussels in their native habitat is that their densities aren' t anything like we see over here because so many birds and fish eat them, " she said. " So the more things in Lake Champlain or any place in North America that learn how to eat zebra mussels and recognize them as food they' ll have some impact on the population and they won' t be quite as devastating."

Although Watzin is encouraged by the research, she emphasized that the discovery will not solve the spread of the mussels.

" I don' t hold out a lot of hope for anything controlling them, " she said. " I think we just have to get used to the fact that the ecosystem is going to be different. It' s going to be a different lake in 10 years than it is now."

The zebra mussel arrived from Europe on ships that unloaded in the Great Lakes in the late 1980s. They have since invaded every major water body east of and including the Mississippi River.

They were first spotted in Lake Champlain in 1993 and have infested the entire lake since then, encrusting rock ledges, shipwrecks and docks. And the population continues to grow.

The mussels block water intakes and sewer lines. They also choke out native mussels by growing on top of them. They eat plankton and filter algae and other food sources for fish.

The result is clearer water " at the expense of the food chain, " said Watzin.

A diet of zebra mussel can be detrimental to some fish.

White fish in Lake Michigan are eating the mussels, and their health is declining, said Tom Nalepa, a research biologist with the Great Lakes Environmental Research Lab in Ann Arbor, Mich.

" The population is going down, their weight is going down, " he said. " While their stomachs are full of shells, they are not getting nutrition, " he said.

Watzin' s research is not the first discovery of fish eating zebra mussels but its significance will depend on the extent of the feeding.

" We find zebra mussels in the diet of sheepshead, " said Jeffry Miner, associate professor of biology at Bowling Green State University in Ohio, who does zebra mussel research in the Great Lakes. " It' s perfectly expected that they would (eat them.) They are bottom feeders."

He has studied whether the round goby fish, which feeds on zebra mussels in the Great Lakes, could reduce the population there.

" We find in experiments we can reduce the number of zebra mussels, " he said.

The gobies eat the smaller mussels, which may reduce the number of adults, he said.

The ecosystem of Lake Champlain could have different effects on zebra mussels. Because the lake has less calcium than the Great Lakes, zebra mussel shells are weaker.

" There could be a slight combined effect, " said Miner. " There' s not enough minerals for the shells to be strong. That might allow sheepshead to have just enough advantage. What might happen in Lake Champlain is predators that aren' t effective in Lake Erie could be effective in Lake Champlain. In Lake Champlain the sheepshead may succeed."

 

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