On the Mississippi River near Cassville, John Lyons of the Wisconsin Department of Natural Resources is looking for Asian carp. Twice a summer for the last five years, Lyons has dragged the river bottom with trammel nets, seined the near shore, and electroshocked the shallows, in search of silver and bighead carp.
"So far, fortunately, I can say we have not seen or heard of the carp in that area," says Lyons, a fisheries scientist with the DNR's Fish and Habitat Research Section.
The bad news? Both species of the feared invader can be found in ever-growing numbers in the Mississippi below Cassville. And there have been at least 10 sightings of bighead carp above Cassville in the last decade. In early October, a commercial angler netted a 28-pound bighead in the Mississippi's Lake Pepin, near Frontenac, Minn., 150 river miles north of Cassville. It was the second bighead found in Pepin in the last four years.
Bighead and silver carp are a huge environmental problem. Because they're so prolific (bighead females can deposit millions of eggs a year), they can push out native fish species, as they've done in parts of the Mississippi and Illinois Rivers.
Bighead carp can grow to well over 80 pounds, silver carp in excess of 25 pounds. Voracious filter feeders, they suck up plankton, the base of the river food chain. Silver carp filter out plankton at the rate of two to three times their body weight every day. And there's a good chance these fish will make their way into Wisconsin's inland waters - if they haven't already.
Natives of China, bighead and silver carpwere imported to the United States in the 1960s by Southern fish farmers who wanted these aquatic vacuum cleaners to keep their rearing ponds spic-and-span. But the carp escaped into the Mississippi River watershed. Today, silver and bighead carp are found in more than a dozen states along the Mississippi, in many places as the dominant fish species.
The DNR's hope, says Lyons, is that dams and locks on the Mississippi River - especially the Keokuk Dam and Lock on Iowa's southeastern tip - will keep Asian carp below Wisconsin. The dam is high enough that, even during flood-stage, it's an effective fish barrier. Below Keokuk, Asian carp are abundant.
There are 17 dams and locks straddling the Mississippi River above Keokuk, and Asian carp numbers drop past each dam and lock. Lyons thinks this "gauntlet" has greatly slowed the invaders' northern migration.
Grass carp, another China import, escaped Southern fish farms a couple decades before the other two carp, and quickly established itself throughout the middle Mississippi River. Yet it hasn't made much of a move north. Lyons believes grass carp prefer warmer climes, and hopes bighead and silvers feel the same way.
But Denny Caneff, executive director of the Wisconsin River Alliance, says Mississippi River dams "all have locks" that let through boats, barges and fish. "So the lock-and-dam system on the Mississippi is not going to stop those carp. To get to Lake Pepin, that carp would've had to clear probably 23 locks and dams. And it did!"
With carp as far north as Lake Pepin, there's nothing to stop them from swimming up the Wisconsin River, which empties into the Mississippi just south of Prairie du Chien. Caneff says there are 26 hydropower dams on the Wisconsin between Rhinelander in the north and Prairie du Sac in the south. And these dams are actual barriers, without locks.
Still, says Caneff, "Asian carp could get up as far as Prairie du Sac. Which would be really interesting, if you think about it, given all the recreational value of the Lower Wisconsin River."
Maybe "interesting" isn't the right word. More like "frightening." Just ask the folks in tiny Bath, Ill., population 350, south of Peoria on the Illinois River.
Asian carp got there in the mid-1990s. According to Greg Sass, director of the Illinois River Biological station, there are now a staggering 2,900 silver carp per river mile near Bath. Bighead numbers have also grown exponentially.
Silver carp leap out of the water at the sound of boat engines, 10 feet or higher, and can smack right into boaters, anglers and water-skiers. Locals started the "Redneck Fishing Tournament" several years ago to focus attention on the problem, with people netting airborne carp for prize money.
While the national media got a few chuckles from these "redneck" anglers, in fact the invader fish have made sections of the Illinois unusable. Sass says people have had noses and jaws broken by kamikaze carp.
Meanwhile, native fish populations near Bath are in decline. Locals blame the carp. While a direct link can't be proven, Sass thinks the carp filter out so much plankton that they've disrupted the river's food web.
While hoping Asian carp won't arrive here in substantial numbers, the DNR is preparing for the worst. For example, the agency is now designing a fish-passage system to let fish move across the hydropower dam at Prairie du Sac. Lyons says the DNR will "sort through" the fish, to stop Asian carp from getting into the upper part of the Wisconsin River.
"That's a design consideration we're building into it," says Lyons, "for that very reason: There's a good chance the Asian carp might show up."
Carp move up the Mississippi
Great maps of these fish and their distribution were put together by Milwaukee Journal Sentinel in 2006, using U.S. Geological Survey data. This map and others by the agency include:
- The Journal Sentinel compilation map (PDF)
- A USGS map on bighead carp
- A USGS map on silver carp
- Before and after Fish and Wildlife Service maps of the carps' spread (PDF)
Madison lakes also at risk
The Dane County Lakes and Watershed Commission was recently awarded a $14,500 grant from the DNR to create an aquatic invasive prevention-and-control plan.
"It includes funds for hiring a limited-term employee to help us pull together information about not only our current invasives, but threats like Asian carp," says Sue Jones, the commission's watershed management coordinator.
There's no direct connection between the Wisconsin River and the Yahara chain of lakes in Dane County. So if Asian carp travel up the Wisconsin River, as feared, Madison-area lakes would not automatically be affected.
But Jones, who plans to attend a 2008 workshop on the Asian carp problem in Illinois, warns that aquatic invasives have a way of moving between watersheds.
"The way we got [invasive] Eurasian water milfoil [into Madison-area lakes] may not have been from the Wisconsin River," she says, "but it may have been from a watershed or basin to the east of us, just by boat transport."
