Fisheries biologist Eric Gittinger can't forget that first face-to-face encounter. Every time he bends over to peer into a microscope or pore over a data table, the reminder comes as a throbbing, headache-inducing pain in his neck. "I had an MRI last week, and it doesn't look like there's any spinal damage," he says. "But anytime I look down, it is pretty uncomfortable." ¬ The cause of Gittinger's condition literally leapt out of the water on a late
afternoon in July 2000. Just out of graduate school, he was working for the Illinois Natural History Survey--a research arm of the state's Department of Natural Resources. He was sitting on the edge of a boat that was trolling down a wide-open stretch of the Mississippi River just south of Alton, Illinois, when a six-pound silver carp flew through the air, struck the back of his head and caused a neck injury.
Since then, the young biologist has developed a reputation among his co-workers for being something of a carp magnet. "I'm the leader for being hit the most times. Probably over 30 times in the last two years," he says with a shrug. So far this year, by Gittinger's count, he and his colleagues have been struck by leaping carp 19 times--and at least 70 fish have jumped into the boat. "I've only been here two years, and I've already had to fill out two workers' compensation forms for people who've been struck by carp," says Gittinger's boss, John Chick, the team leader at the Natural History Survey's Great Rivers Field Station.
Absurd as it seems, incidents of leaping carp striking boats and boaters has become a fact of life on many stretches of the Mississippi River in recent years. That's because there's been an explosion in the population of two closely related species of Asian carp: bighead and silver. No one knows for sure what causes these carp to jump. Gittinger and Chick note that the fish seem to be stimulated by boats traveling at a fast idle. Gittinger also theorizes that bigheads and silvers might be mistaking approaching boats for the sorts of big predators that inhabit their native waters in Asia, such as freshwater porpoise.
Earlier this summer, after Gittinger and his co-workers netted some of the fish to perform stomach-content analysis, they realized they were three fish short of their desired sample size. Instead of putting the nets back out, they simply motored into a school of the fish and waited for them to start flying out of the water. "It only took a minute or two and we were done," Gittinger recalls.
Unlike the common carp--brought from Europe to the U.S. in 1831, and now ubiquitous in Minnesota waters--bigheads and silvers are relative newcomers to North America. Experts are already worried, however, that the fish may be wreaking havoc on the aquatic ecosystems they colonize, possibly dwarfing the impact of previous exotic invaders such as the zebra mussel and the sea lamprey.
Asian carp were initially imported from China in 1973 by catfish farmers in Arkansas, who were looking for ways to improve water quality in their rearing ponds. As filter feeders, silvers and bigheads strain plankton from the water for sustenance, which can help control bothersome algae blooms. And since the fish have a voracious appetite (they can consume half their weight per day) and considerable heft (up to 100 pounds in their native Asia, 50 pounds in the southern U.S.), they initially proved to be a boon to the growing aquaculture industry.
In the early Nineties, Asian carp began to show up in the southern reaches of the Mississippi River. Most researchers believe that the fish escaped from the catfish ponds during floods; others theorize that some may have been deliberately introduced. Whatever the case, the fish have steadily moved up the Mississippi and its tributaries, advancing at a rate of 35 to 50 miles a year.
Silvers and bigheads have yet to reach Minnesota waters, but scientists say their arrival is a virtual certainty. In May, a commercial fisherman netted a 13-pound bighead some 40 miles south of LaCrosse, Wisconsin. That marked the fish's northernmost appearance on the Mississippi (a 150-mile advance from previous sightings).
"It's alarming," observes Jay Rendall, coordinator of the exotic-species program at the Minnesota Department of Natural Resources. "They're definitely on their way. I keep hearing that they're stacked up like cord wood at some of the dams in Iowa." Rendall cautions that he can't be certain what effect the fish will have once it arrives in Minnesota. But he is wary: "My gut instinct tells me there will be a pretty dramatic impact. In some of the states where these fish are established, they've essentially taken over the fishery."
In fact, it's gotten so bad in Illinois that commercial fishermen have abandoned some stretches of the Mississippi because Asian carp are constantly fouling their nets. In October 1999, a biologist at the scene of a large fish kill in a Mississippi backwater south of St. Louis calculated that an astounding 97 percent of the dead fish were Asian carp; near Alton, Illinois, where biologist Gittinger was hit in the head, the population has increased exponentially over the past three years and shows no sign of abating.