Invasive carp are heading toward Chattanooga, threatening the region's renowned freshwater ecosystem and posing risk to recreational water users and fishermen.
The non-native fish are making their way through the U.S.'s main river systems via locks, and biologists, federal officials and fishermen are working to combat them as they spread.
"Basically, we have silver carp that have been in the Mississippi River system for quite some time," U.S. Fish and Wildlife Service biologist Angie Rodgers said. "They have been on this progression up the tributaries, and we're starting to see them move upstream in some of our major waterways."
Asian carp were brought to the southern U.S. from southeast Asia in the 1970s to help clean retention ponds, but the plan backfired when the fish escaped into the Mississippi River system during flooding and migrated to the Missouri and Illinois rivers. The fish have been moving throughout river systems in the eastern U.S. since, and with no North American fish large enough to eat adult Asian carp, they continue to spread.
Three species of Asian carp are considered invasive and threatening freshwater systems across the eastern U.S.: silver, black and bighead carp. Silver and bighead carp are capable of eating 5-40 percent of their body weight each day, according to U.S. Fish and Wildlife Service research.
Black carp bring unique challenges for the Chattanooga area. They feed primarily on mollusks, threatening native mussel and snail populations. Forty-two known species of mussels in Tennessee are currently on the federal endangered list, and several species have already gone extinct, according to the Tennessee Wildlife Resources Agency.
"Tennessee is world-renowned for having a high biodiversity of mussels," Tennessee Wildlife Resources Agency Chief of Fisheries Frank Fiss said. "We're concerned about what a mussel-eating fish that gets to be 100 pounds could do to a mussel community on the Tennessee River. Right now, they're in a low abundance, but they may not stay that way. We just don't know."
The most looming threat for the area is silver carp heading toward the Tennessee River system. The fish tend to populate a reservoir and migrate to the next one, moving quickly upstream as locks open for transportation. Biologists with the U.S. Fish and Wildlife Service have found carp as close as Decatur, Ala., meaning they only have a few locks to navigate before entering Tennessee.
"They feed on plankton, the little microscopic animals that float around in the water, and why this is a problem is all of our native larval fish feed on really small animals like plankton early in their life stages, especially our large river fish," Tennessee Aquarium biologist Bernie Kuhajda said. "The silver and big headed carp are large river fish, so they're directly competing for food that our native fishes need."
Silver carp pose numerous risks in addition to outcompeting native species for plankton. They are known to feed on larval fish, an important part of the food system. They can also densely pack a river system, stressing other fish and crowding them out. That impact on the freshwater ecosystem is enough to alarm biologists, but the risk doesn't end there.
Silver carp leap out of the water when threatened, an action often prompted by something as simple as a passing boat, and at an average of 40 pounds, they have caused serious injuries to boaters.
"If you get a 40-pound fish in your face going 40 miles per hour, it can kill you," Kuhajda said.
Federal and state governments have spent millions of dollars trying to combat the fish and have proposed hundreds of millions of dollars in additional funds to stop their spread.
Eradication is the ultimate goal, Rodgers said, but federal agencies are actively working to slow their spread and control the population.
There are several ways federal agencies are looking to do this. One of the most successful, Fiss said, has been working with commercial fisherman on incentives for carp fishing. Solutions still being looked at include a possible stimulus plan that would give fishermen extra money when they remove carp from waterways. Federal groups are also testing sound and light deterrents to keep the fish from entering locks and spreading.
"They've been able to scare carp, basically, in ponds in research situations, but we haven't done it in a big river like the Tennessee, yet," Fiss said. "There are ongoing projects to do that in Kentucky and other places now."
Part of the problem is no one quite knows what they're up against, Fiss and Rodgers said. In terms of overall aquatic research, this problem is relatively new and the issue has not been fully studied. Biologists don't know how many carp are spreading or how quickly they could get here.
"The magnitude is that it could get a lot worse, but we're not happy with where it is," Fiss said. "We don't have a clean way to get metrics on a carp invasion. This is the first time it's happened."