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Ocean Watch

Susan Scott

Friday, May 7, 2004


Bighead carp threaten
the Great Lakes


While visiting my hometown in Wisconsin this week, I hiked along a breakwater to a lighthouse in nearby Lake Michigan. There, the fresh breeze, choppy swell and endless view reminded me of the ocean. This Great Lake smelled like the sea, too, but clearly this wasn't salt air. It was fish air and I loved it.

The Great Lakes resemble the ocean in some negative ways, too.

Both are threatened by various human activities, and both harbor what people consider bad fish. In Hawaii the villains are sharks and the introduced blue-striped snapper or taape. Here it's carps.

Although all four species of introduced carps are a threat to the Great Lakes, the big hazard right now is the bighead carp. These fish don't have teeth and aren't aggressive, but they're scaring people here, for good reason. Bighead carp have the potential to wipe out nearly every living creature in the Great Lakes.

Bigheads aren't your average carp. These Asian imports grow to 110 pounds and can measure up to 50 inches in length. To reach this enormous size, they eat half their weight in plankton every day.

And that's the problem. By gobbling up most of the Lakes' tiny plants and animals, bigheads hit the food chain where it hurts the most: at the bottom.

A shortage of plankton squeezes out the little fish that survive on it. And that's it. With no small fish, the trout, salmon and other fish-eaters in the lake are done for.

Anglers love fishing for trout and salmon, and lots of people love the anglers. The Great Lakes sports fishing industry generates an annual $5 billion to the region.

It was also economics that brought bigheads here in the first place.

Southern fish farmers imported these carp in the 1970s to clean algae from their ponds. The fish escaped during floods about 10 years ago and have been inching toward the Lakes since then.

People are right to worry. No state or federal laws exist prohibiting trade in, or release of, bighead carp. And the carp are definitely coming. A 38-pound bighead was recently caught in a Chicago lagoon only a few miles from Lake Michigan. Also, to date, four bighead carp have been caught in Lake Erie, and a snorkeler there spotted two more near a river entrance.

All the Great Lakes are connected.

Because the four bigheads taken from Lake Erie were all adults, biologists don't think the fish bred there. But with no regulations on these rapidly reproducing fish, it's just a matter of time.

Today, it's easy to buy bigheads in both Canada and the United States. One fish market in Illinois sells live bigheads for $1.29 per pound. It's up to the buyer to kill them.

Some softies, however, can't do it. They feel sorry for the gasping fish and set them free.

Alien species in the once-isolated Great Lakes is an old problem, dating from the early 1800s when the first man-made ship canal to the Lakes opened. A century later, people reversed the Chicago River's flow, linking Lake Michigan to the Mississippi River.

Since then the largest freshwater ecosystem on the world has been open to invasion from both sides.

People are currently working to keep the carp out of the Great Lakes in the form of electric fences, new legislation and public education.

There's hope yet for the health of the Midwest's oceans.



See the Columnists section for some past articles.

Marine science writer Susan Scott can be reached at http://www.susanscott.net.

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