Asian carp cause problems in the region's waterways
Wednesday, August 20, 2008
A quiet invasion makes for troubled waters on the area's big rivers and some related backwater slough lakes.
The lower Ohio, Tennessee, Cumberland and Mississippi rivers nowadays teem with a pair of carp species that aren't native to American waterways. Indeed, bighead carp and silver carp are Asian in origin. Arkansas fish farmers imported the fish as pond cleaners in the 1970s. But the Asians escaped their commercial surroundings when floodwaters came calling to lowland ponds in 1993.
In the 16 years since their accidental release, bighead and silver carp proliferated in the Mississippi River, then blew up in numbers in all the major tributaries, including the lower Ohio and the far downstream ends of the Tennessee and Cumberland.
Rather than being a mere addition to rivers, streams and lakes, Asian carp force themselves among those swimming local waters. But that's especially true for huge numbers of large fish -- silver carp easily reach 30 pounds and bighead carp potentially double that size and more.
Paul Rister is the Kentucky Department of Fish and Wildlife Resources fisheries biologist for the state's westernmost waters. He said vast numbers of Asian carp could undermine the food base for other fish. As filter feeders, the bighead and silver carp strain small organisms, algae and plankton, from the water. The vast population of them might dramatically reduce this material, which is a basic food source for juvenile fish of many species and a primary food source for shad and paddlefish.
"Shad are filter feeders, too, and they're a chief food for most sport fish species," Rister said. "If shad go down because of the competition from Asian carp, then we don't have as much for sport fish to live on.
"One of our chief concerns is for paddlefish, which compete directly with Asians because they're all filter feeders," Rister said. "Paddlefish are clearly in poorer condition than what we've seen in the past.
"We've seen bighead and silver carp use the oxbow lakes that are occasionally flooded by the rivers as nursery areas," he said. Oxbow lakes are bow-shaped lakes formed in a former channel of a river.
"The paddlefish use them, too, and they compete for the same food there," Rister said. "The paddlefish we've seen in the oxbows are emaciated."
Fishing pressure to hook paddlefish for their eggs compounds the species' problems. Paddlefish eggs satisfy an inflated caviar market as a substitute for sturgeon roe.
Adult Asian carp found in Kentucky Lake and Lake Barkley are thought to have passed through navigational locks to reach the reservoirs. They are not thought to be reproducing in the lakes, however. Thus the numbers of bighead and silver carp reportedly are modest in comparison to the masses seen in the rivers and river-flooded oxbow lakes.
"They do especially well in the bottomland lakes," said Doug Henley, a Kentucky Department of Fish and Wildlife Resources Ohio River biologist. "To reproduce, they need running water like they have in the rivers, but the larval fish that they produce by spawning need the backwater areas as nurseries. There, they really compete with small native fish for plankton.
"The 2- and 3-inch crappie that are in the oxbows might end up without enough food when there's a mass of Asian carp in there, and that's where you get a bottleneck of all these mouths to feed and too little food," Henley said. "That's one way you get stunted fish."
A wild abundance of fish might seem to be a bounty instead of a blight to a commercial fisherman, but it all has to do with public demand.
"They're tasty fish, but there's no local market for Asian carp," said Ronnie Hopkins of Ledbetter, a commercial fishermen and one of a few who nets silver and bighead carp intentionally.
"I've got my own market, but I just ship them out as I get orders for them," he said. "I can usually catch all I need to keep the orders filled." Hopkins said existing demand primarily is ethnic in origin, people who are culturally inclined to eating silver and bighead carp. But with the huge resource of Asian carp in area rivers and lakes, consequently, processing facilities are needed to turn the invaders into ground fish patties or other forms that can be used in the mass market.
In the interest of improving the fish populations on some of Ballard County's state-owned small lakes, Hopkins has done some contracted netting to remove Asian carp from them. He also nets on the Ohio as demand rises for Asian carp as a food fish.
"We're eat up with them, but you have to go to the kind of places they go to catch them," he said. "On the river, they like to go where there's swift water next to dead water and net along the edge there."
Hopkins said silver carp are notorious for jumping when disturbed, and this behavior has proved painful for fishermen and boaters in this region. "They're shaped like torpedoes, and they hit just as hard when you're running along in the boat and you run into one," he said.
"I was just out running a net and had about 15 of them jump into the boat while I was working," Hopkins said. "One of them hit me in the back, and it was like somebody hit me with a ball bat."
The U.S. Geological Survey has issued information cautioning boaters about the jumping behavior of silver carp. The warning equates a leaping silver carp striking a power boat passenger with getting hit with a thrown bowling ball.
Asian carp also damage commercial fishing equipment, Hopkins said. A large school of these bullet-shaped exotics can destroy fishing nets designed for other species, he said.
Ohio River biologist Henley said the stronghold of the Asian carp seems to be in the lowest portion of the Ohio, with both silvers and bigheads growing markedly less plentiful in the Louisville, Ky., area and upstream.
Hopkins said despite their downstream plenty, Asian carp seem to be still on the upswing in the lower reaches in the Ohio River and in the lowest portions of the Tennessee and Cumberland.
"Their population is getting stronger every year," he said. "They're taking over."