Silver carp. (Photo: Doug Canfield, USFWS)

An unwanted guest, the silver carp has recently invaded the Tennessee River in both Tennessee and Alabama.

You may have seen videos of silver carp jumping out of the water in a frenzy and slamming into boats.

“They’re like the feral hogs of the water—at least silver carp are as big a threat,” said Nick Nichols, Alabama Wildlife and Freshwater Fisheries Division fisheries section chief.

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Just as feral hogs compete with native wildlife for food and habitat resources, silver carp can interrupt the natural food chain, with native species being devastated. Silver carp are one of four species of Asian carp that has been released in the U.S., the others being bighead carp, grass carp (white amur) and black carp.

Silver carp and black carp are considered the greatest immediate threat to the aquatic resources of Alabama and Tennessee.

Many people who have ponds or lakes are familiar with grass carp, which were introduced into the U.S. in the 1960s to control aquatic vegetation.

Nichols said there is no evidence so far that grass carp have adversely impacted aquatic ecosystems in Alabama.

Bighead carp, filter feeders that primarily feed on zooplankton and can weigh 80 pounds or more, came to the U.S. in the 1970s.

The black carp has the potential to be a devastating invasive species because of its food preferences.

“The black carp is a species that very much worries us,” Nichols said. “This species looks very much like a grass carp. They were accidently brought into the country with loads of grass carp because they look so much alike. The problem is that black carp feed almost exclusively on snails and mollusks.”

States such as Alabama, Tennessee and Kentucky have a huge biodiversity of aquatic mollusks, which includes snails and mussels of conservation concern, and the black carp could have a big impact on those species.

But the greatest concern currently is the silver carp.

Nichols said:

The silver carp is also a filter feeder. It filters not only zooplankton but also phytoplankton, the microscopic plants. So they’re feeding right at the bottom of the food chain. By doing so, they’re competing with every other fish species in that body of water for the food supply. If they’re cropping off that zooplankton, that’s taking food out of the mouths of the native species, like the shad and bluegills.

Also, silver carp don’t disperse but stay in large schools, thus overwhelming some systems, with the silver carp being the only thing left.

Kentucky Lake on the Tennessee River and adjacent Barkley Lake on the Cumberland River have both been hit hard by a growing silver carp population that has had a severe impact on sportfishing. More recently, silver carp have spread upstream into Pickwick Lake.

As a response to the threat, Alabama has joined forces with the Tennessee Wildlife Resources Agency and the Mississippi Department of Wildlife, Fisheries and Parks to mitigate the spread of silver carp.

Twenty-eight states in the Mississippi basin have joined to form the Mississippi Interstate Cooperative Resource Association.

The U.S. Fish and Wildlife Service, the U.S, Geological Service, the Tennessee Valley Authority, the U.S. Bureau of Reclamation and two Native American tribes are also members of the coalition.

Tennessee Tech has received federal funding to monitor numerous lakes, including Pickwick, for silver carp. One goal is to catch silver carp and insert sonic tags for tracking their movements.

“There’s not much to stop them from moving upstream,” Nichols said. “Typically, they will go through the locks.”

He said several methods are being evaluated to deter the spread of silver carp, including electronic barriers and large hydrophones to scare the fish away from the locks.

According to Nichols, several elements need to come together in order for the fish to have a successful spawn.

“If we’re lucky, these silver carp in Pickwick will die of old age before they can get off a big spawn,” he said. “That assumes we don’t get more fish from Kentucky. If they do get established, it will have a big impact on the native game and nongame fish species. And that’s not good news.”

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