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PRI's Environmental News Magazine

Fish Kill

Air Date: Week of February 16, 2007

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A disease is killing fish in the Great Lakes. Scientists believe the virus may have first come from Europe on the ballast of a ship and spread from there. As Lester Graham of the Great Lakes Radio Consortium reports, biologists and the federal government are trying to figure out how to prevent the spread of the virus, without causing harm to businesses that rely on fish shipments.

Transcript

CURWOOD: A fifth of the fresh water of the world is found in the Great Lakes along the US- Canadian border, and more and more it seems these lakes are in trouble. Changing rain patterns have kept the lakes lower than usual over the past few years, and they’ve also been laced with pollutants and invasive species. Now the lakes are facing a microscopic threat in the form of a virus that can make fish bleed to death. Lester Graham of the Great Lakes Radio Consortium has more.

GRAHAM: The disease that’s killing fish is called Viral Hemorrhagic Septicemia - or VHS. Jim Diana is a fish biologist at the University of Michigan who’s been looking into what it does to fish.

DIANA: The virus causes really kind of a general systemic deterioration. Ah, most noticeable, sometimes they’ll develop sores or lesions on the outside of the body, but they often will die without really external evidence at all.

GRAHAM: Basically, the fish die from internal bleeding. For several years there have been die-offs in the St. Lawrence River, which connects the Great Lakes to the Atlantic Ocean. But researchers weren’t able to confirm the cause was VHS. Then last summer in Lake Saint Claire - the lake near Detroit that lies between Lake Huron and Lake Erie - Jim Diana says fish die-offs were confirmed to be caused by VHS.

DIANA: And since then, they’ve found it in quite a few other species, something like 20 other species, so it’s quite widespread.

GRAHAM: Since then, the virus has been detected in Lake Huron. It’s not clear how the virus got here. But the first strains of VHS were discovered in Europe about 50 years ago. Researchers guess that infected fish hitchhiked in the ballast tanks of ships or a live fish shipment escaped into the St. Lawrence River and it’s spread from there.

Biologists say the spread of VHS is NOT expected to wipe out fish in the Great Lakes. It is causing some real concern.

GADEN: We’re not talking about a couple of fish here, we’re talking about large fish kills. And VHS is present in those and implicated in the deaths of those fish.

GRAHAM: Marc Gaden is with the Great Lakes Fishery Commission. Gaden says because stocking fish is a big industry, there’s a lot of fish shipped between the U.S. and Canada and between one state and another.

GADEN: There is a movement of fish, fish eggs and other fishery related things like, um water that’s used in the fish stocking trucks, things like that. There’s aquaculture that occurs, fish farms in the Great Lakes basin. The Departments of Natural Resources harvest fish eggs to use in their stocking programs and the fish themselves are stocked.

GRAHAM: So the chance that the virus can be spread by all those fish moving around is significant. The federal government thought it was such a risk that it banned all live fish shipments. Most of the Great Lakes states and commercial fishers quickly appealed that ruling. They said it was overkill. They persuaded the feds that state testing would reduce chances that VHS would be spread by transport.

So, the federal government backed off a bit. But restrictions are still causing some problems. For example live fish that are not going to be put back into the lakes, live fish that are headed for dinner plates at restaurants still have to be tested. And VHS poses no risk to human health.

The Great Lakes states, the U.S. and Canadian governments, are still trying to figure out how best to prevent the spread of VHS without hurting the businesses that rely on live fish shipments any more than necessary. Meanwhile, some scientists say the virus will simply have to run its course. Those fish that survive will build up a natural immunity to VHS.

For Living on Earth, this is Lester Graham.

 

Links

Great Lakes Fishery Commission

 

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