Since the discovery of carp DNA in the waterways near Chicago in 2009, the Asian Carp Regional Coordinating Committee, which consists of federal, state, and local agencies, has spent $100 million on carp research and control. The official line is that if any fish are living north of the electrical barriers on the canal, they are sparse and scattered, too few to reproduce in the Great Lakes. Though he doesn’t disagree, Chapman adds a note of doubt. “They’re very cryptic. They’re wanderers—an open-water fish. They could be out there.”
Duane Chapman knows his rivers, but the scientists who study the lakes are less impressed by the carp threat. “It’s way overhyped,” says Gary Fahnenstiel, an aquatic biologist with the Great Lakes Environmental Research Laboratory, which is run by the National Oceanic and Atmospheric Administration. One reason is that the nutrients and plankton in the waters of the Great Lakes are not merely limited, they are crashing, due to a different exotic species, the zebra mussel, and its cousin, the quagga mussel, two invaders that stowed on ships from Europe in the 1980s. Having multiplied on the bottom of the lakes, the mussels are straining the lake water of most of its plankton. One result, Fahnenstiel points out, is that the population of a shrimp important to the diet of whitefish and salmon is plummeting. The mussels’ threat to the fishery is not hypothetical—it’s actually happening.
As the mussels transfer nutrients from the upper levels of the lakes to the depths, yet another exotic species, the round goby, has exploded. The round goby is a small fish that feeds on the bottom, unlike the silver and bighead carp. In effect, the mussels bring the food supply down to the level where the gobies can get it. Indeed, it was the round goby that prompted the installation of the first electrical barrier in the Chicago Ship and Sanitary Canal 15 years ago. The barrier was meant to keep the goby out of the rivers, rather than the carp from the lakes, and it failed. At any rate, should a wave of carp make it through the canal or penetrate the lakes by another route, they will find little food to sustain them. Chapman counters that they might concentrate their diet on a blue-green algae, Microcystis, which the mussels don’t eat, or turn to a clumpy, shoreline algae known as Cladophora. They might get enough to eat that way, he says.
Survival of the Asian carp in the deep,
windblown, and, in winter, ice-covered waters of the Great Lakes is one thing, but development of a breeding population there is quite another. Silver and bighead carp cannot spawn in lakes; instead, they must find their way into river habitat. Their eggs and larvae need to drift for a period in a mild, steady current, or else they will sink and be smothered on the bottom. Chapman calls the spawning requirements of silver and bighead carp their Achilles’ heel because the rivers feeding the Great Lakes—assuming the fish could discover them—tend to be fast, rocky and short, not ideal for nursing carp.
Most probably, then, Lakes Michigan, Superior, and Huron will not support Asian carp in worrisome numbers. NOAA’s Fahnenstiel was not as confident about the unsuitability of Lake Erie. Erie could well host carp. The smallest and warmest of the Great Lakes, Erie has sheltered coves containing algae and a meandering river, the Maumee, for potential spawning. Three bigheads—isolated individuals—have been pulled from its waters by fishermen, though none have been seen lately. “Those were big fat fish,” Chapman cautions. “Lake Erie looks like a pretty good home for [populations of] bighead and silver.”
The USGS’s Columbia Environmental Research Center (CERC), where Chapman works, is in Columbia, Missouri, near the eponymous river, some 350 miles from Chicago and the front of the invasion. CERC maintains and studies carp of all sizes: adult bigheads and silvers in a dozen ponds; six-inch juveniles, swirling in tight schools in tanks; eggs and larvae floating in beakers; even carp in an aquarium behind the receptionist’s desk. Chapman directs a dozen scientists and staffers on various explorations of carp behavior and physiology.
There is pressure on the scientists to understand the life history of the two species better so that the agencies can attack them more precisely. For instance, when alarmed, juvenile Asian carp emit “aggregation pheromones,” biochemical signals telling the fish to bunch up. If the pheromones can be decoded and synthesized, they might be used to disrupt migration and spawning. The phases of egg hatching and larval development are the subject of another project. Chapman and colleague Amy George published a paper last year that aimed to predict the growth rates and temperature and current requirements of juveniles drifting in rivers. The work might allow wildlife managers to prioritize the tributaries that they ought to check for carp. A new finding that came out of the study was that, very soon after hatching, larval carp are able to swim vertically, fighting off their tendency to sink toward the bottom.
A post-doctoral researcher, Karthik Masagounder, who is in charge of nutritional studies, took me around a lab building at CERC. Masagounder records the calories in the dried algae that he feeds to his captive carp, and then he tracks the weight of the fish, which depends as well on the temperatures maintained in the tanks. He has put together a mathematical model of the calorie exchange. “We want to know,” he explained, “if they colonize the Great Lakes, how will they grow? With a certain amount of plankton available, the model will tell us their weight gain in a year.” Masagounder climbed a ladder onto the side of a large, round tank. It was covered with mesh, lest the subadult silver carp jump out. With a small dip net, the researcher tried to catch one. Cautiously he edged the net under the mesh. But the little fish went bonkers, leaping and splashing as its relatives do on the Illinois, and Masagounder backed off, shaking his head and remarking, “They make my life miserable.”
That is something Duane Chapman would never say about a carp. “They drive my waking moments, and I’m thinking about them at 3 a.m.,” he reflects. The 53-year-old Chapman is a commanding figure. With his resonating bass voice and 6’4” height, he dominates conversations with his peers, whether at formal meetings or standing around the water cooler. Although his focus these days is experimental, he has paid his dues in the field. “I’ve spent thousands of hours getting carp-slimed on the river,” he says, sounding proud. One day when he came home from work, he smelled so bad that his daughter, running across the lawn to greet him, stopped and ran the other way. If you email him a technical question about fish slime, he may send you more than you need to know, such as the fact that “fish have mucous on the outside of their bodies for the same reason that we have mucous inside our noses. It makes it hard for things we don’t like to get a purchase on our tissues.” And: “I have to admit, silver carp and bighead carp do seem to have a bit fishier smell to them than most, and I think that is something in the slime, plus the fact that their feces are usually runny and tend to run out and go everywhere when the fish jump in your boat. And the green color of the feces does not help.”
I soon realized that, though his mission is to stop them, Duane Chapman is fond of Asian carp. In his office he shows off a rack of teeth that were taken from a monstrous, 106-pound bighead. Placed at the very back of the throat near the gullet, the small teeth grind the plankton just before the food goes down. When he diagrams how the fish transfers the plankton from the water to its gill-rakers and then to its gullet, Chapman says, “It’s such a cool thing they’ve got, to channel their food.” Likewise, when reporters seek his views on the threat to the Great Lakes, his passion for the subject can encompass all sides of the issue, usually sketching how the carp could adapt to the lakes, but other times arguing why they might not. When I noted that three bigheads had already been caught in Lake Erie, he said sharply, “Do you know how hard it is to stock a big lake with Asian carp? The Europeans really had to struggle to establish a population.”