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Great Lakes Article:

Outdoors: Non-native fish could threaten river's food chain

08/26, 2002

By Ben Moyer

Western Pennsylvania waterways may be the source and the destination for non-native fish, and that has the potential to disrupt ecosystems in their new environment.

Flathead catfish, including several young, have been caught below the Safe Harbor Dam on the lower Susquehanna River this summer. Since 1997, flatheads have also been caught in the Delaware and Schuylkill rivers, and in the Blue Marsh Reservoir, all in eastern Pennsylvania.

The species is not native to eastern Pennsylvania, but it is a natural inhabitant of the Ohio River drainage, including the Allegheny and Monongahela rivers in Western Pennsylvania. Flatheads have been known to reach 100 pounds and are active predators. The Pennsylvania state record is more than 40 pounds.

It is not known how the flathead catfish became established in rivers in eastern Pennsylvania, but there is concern that its arrival could harm established fisheries there. Where the diets of flatheads have been studied, sunfish, other catfish and crayfish are principal prey items.

Flatheads could disrupt native fisheries both by competing with native fish for food, and by eating native fish directly. In the Cape Fear River in North Carolina, where the flathead has also been introduced, researchers documented a severe decline in native fish populations within 15 years after flathead catfish became established there. Scientists found that after the flatheads had decimated populations of sunfish and other catfishes, they switched to feeding on shad.

That could prove serious on the Susquehanna, where the Fish and Boat Commission has led a cooperative program to re-establish a population of American shad in the river. Shad were abundant in the Susquehanna until early in the 1900s and supported a vibrant commercial fishing industry. Flathead catfish could hinder the reintroduction effort and the 500,000 angler-per-day annual sport fishing the Commission estimates would result.

Mike Kaufman, a Fish and Boat Commission biologist, said, "We're going to start spreading the word that we would like anglers to keep and kill all flathead catfish caught near Safe Harbor Dam on the Susquehanna."

Commission press spokesman Dan Tredinnick added another perspective.

"The flathead is an opportunistic feeder," he said. "If they get the chance, they will take shad. But smallmouth bass [another introduced species in the Susquehanna] love shad also, and at the right time of year a shad imitation is the best lure for smallmouth. We don't necessarily see this as the end to the shad reintroduction."

Flathead catfish are olive to light brown in color, with dark brown to black mottling. They have a wide head that appears flat and depressed, with chin barbels colored white to yellow. Unlike the more common channel catfish, the tail is not forked and it may appear square or rounded.

The best identifying mark is the lower jaw, which protrudes beyond the upper jaw.

According to the Fish and Boat Commission, anglers in Western Pennsylvania should consider the flathead a desirable game fish. In the Ohio drainage, where it has lived for centuries, the flathead poses no threat to native fisheries.

Not so with the bighead carp, which some biologists believe they have spotted recently in Lake Erie. The bighead carp is a native of lowland rivers in eastern China, but has been imported, hatched and raised in hatcheries in the American South. Commercial catfish farmers stock bighead carp in catfish ponds to rid the impoundments of algae, phytoplankton and other undesirable plants. Some fish have escaped and become established in rivers from Alabama northward to the Ohio, Missouri, and upper Mississippi rivers.

Bigheads have grown to 60 pounds in American rivers and 90-pound specimens are not uncommon in Asia. The fish have also been spotted in a canal linking Lake Michigan to the Illinois River, a tributary of the Mississippi.

Biologists believe this could be the route the bigheads used to access the Great Lakes. As with the flathead catfish and American shad in the Susquehanna, the bighead carp could threaten efforts to reintroduce the native paddlefish into the Ohio River in Western Pennsylvania. As a "filter feeder," combing large amounts of plankton and organic debris from the water as a food source, the bighead competes with the native paddlefish for nourishment.

Dr. William Kimmel, an aquatic ecologist at California University of Pennsylvania, is doing research on the paddlefish reintroduction effort on the Ohio River.

"These [bighead carp] have been reported 25 miles from Chicago and from the Ohio River near Wheeling," Kimmel said. "If their food habits include zooplankton at any stage in their life cycles, they could threaten not only paddlefish but larval fishes of many species, posing a threat to the entire river food chain including popular game species."

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