Nonprofit, independent journalism. Supported by readers.


Asian carp expert says the invaders can be beaten

Duane Chapman’s bottom line: “I wouldn’t sell my boat yet.”

Asian carp were probably in the wild almost from the moment they were first imported to the U.S. for use in aquaculture, as a food fish, and as a “biological control” on certain disease-bearing snails and other pests, starting in the late 1960s.

I won’t say that optimism was his theme, exactly, and certainly there was no suggestion that Minnesota relax any of its efforts to keep Asian carp from colonizing its waterways.

But the overall picture that Duane Chapman laid out in his talk in St. Paul Tuesday night, on the subject of “Biology and Management of Asian Carps: Lessons for Minnesota,” was certainly more nuanced, way more interesting and markedly less dismal than the usual disaster scenarios we hear.

This matters because Chapman, a fisheries expert who works for the U.S. Geological Survey’s Environmental Research Center in Columbia, Mo., may know more about these fish than any other single human being. (He is on furlough from USGS nowadays because of the shutdown, but kept his speaking engagement as a private citizen.)

His bottom line: “I wouldn’t sell my boat yet.”

Article continues after advertisement

Some out-of-the-mainstream points from his talk that I found especially interesting:

  • The notion that Asian carp invasions  of American waterways began with their escape from southern aquaculture operations some 15 or 20 years ago is misguided, and the oft-repeated story that implicates the flood season of 1993 is an “urban legend” and “kinda bogus.”

Chapman says Asian carp were probably in the wild almost from the moment they were first imported to the U.S. for use in aquaculture, as a food fish, and as a “biological control” on certain disease-bearing snails and other pests, starting in the late 1960s.

Early escapes from fish farms

As for silver carp, the high-jumping stars of many a web video, the first one found in the wild was caught in Arkansas in 1972 — the same year that the first of that species arrived from China. The first known instance of a bighead carp being caught in the wild was in 1982, he said, but “it’s pretty clear that they were out there longer, because as soon as people started looking for them, they started finding them.”

Silver carp sort of “puttered along” in the wild until their populations surged in the 1990s, to great alarm; on the plus side, their rising numbers drove down the populations of bighead carp, the largest among the four varieties of current concern. And the record includes various instances of Asian carp moving from aquaculture operations into rivers and lakes without managing to survive in detectable numbers.

The significance of all this is that “it took us decades to get to where we are now, not just 15 or 20 years,” which may also mean that “we have decades, probably” to deal with the problem in areas where carp are not yet established. “But now’s the time to be working on it.”

  • The operation of private aquaculture operations based on Asian carp was not as freewheeling, unregulated or incautious as some may assume. In fact, their import and cultivation took place with considerable involvement from the U.S. Environmental Protection Agency as well as state regulators, and back in the 1970s  “biosecurity really wasn’t a word (yet) — we weren’t really too concerned about these fish getting loose.”

Chapman acknowledged that, even then, “some people were incredibly concerned” about the risk that might be posed by these big fish in natural environments, but “there was a feeling among the people who actually had the fish that, so what, if they get loose, they’re not gonna be able to reproduce. Everybody in China was telling us, if they get into our river systems, they’re not going to be able to grow.”

Indeed, the Chinese had gone through their own long struggle to find the correct way of setting up aquaculture operations based on these fish, owing to their sensitivities to a wide range of environmental variables that still are not fully understood. The key was creating artificial conditions to support spawning, and when this was achieved in the 1960s, carp-based aquaculture exploded worldwide.

It takes more than two to make trouble

Because of those environmental sensitivities, the  notion that a single breeding pair of carp — or even a group of 10, the theoretical invading party in one recent study focused on potential threats to the Great Lakes — can establish a population that overruns a natural river or lake system is maybe a bit fanciful.

Map of Asian carp distribution in the US

“Biology is not rocket science,” Chapman said. “It’s a hell of a lot more complex.” And although “we have come leagues and leagues in the last 10 years,” there is much more to know about how these fish operate in natural systems and, by extension, how they can be controlled.

“But we can control them,” he emphasized, and the Jurassic Park-tinged argument that “life will always find a way,” that the fiercest creatures in any system will persist, is simply misguided. “If life always found a way,” he said, “there would be no problem of invasive species,” because established species would withstand the invaders.

Article continues after advertisement

  • Much promising research is being done on control methods, some of it in Minnesota. One possibility is the delivery of carp-killing chemical “toxicants” in forms that are uniquely suited to the filter-feeding varieties and relatively harmless to other fish.

Another is the use of pheromone attractants to lure carp toward control locations or away from protected zones. Still another is research on how to improve the carp-blocking capabilities of existing Mississippi River dams, which Chapman said have actually proved quite effective in slowing the invaders’ upstream migration.

And in the Illinois River, the scene of many a popular jumping-carp video, a commercial fishery that has grown up around silver carp has proven its ability to exert some significant population control. Whether that example can be replicated, though, may depend less on environmental factors than economic ones,  like market demand, prices and subsidies.

Not a delicacy, except heads

Contrary to popular belief, Chapman said, American-sourced carp is not a prized delicacy in Asia — “it’s more like the hot dog of China, the cheapest animal protein you can buy.” The severed, frozen heads of the bighead carp, however, command a premium price.

  • Much remains to be learned, still, on such basic factors as how long a run of river various Asian carp species need for successful spawning, and to what degree various native species will be harmed.

So far, Chapman said, it appears that walleye, perch, sauger and similar species seem to be hurt the worst by invading carp, while bass and bluegills seem to suffer relatively little impact and catfishes seem unaffected. Crappies are a question mark, as are trout, salmon and whitefish. As always, the best way to ensure the health of native species is to protect their habitat.

  • Chapman’s slides included the obligatory leaping-fish photos, including one that featured a bowhunting  angler just before a leaping silver carp sailed into her boat and shattered her jaw. And he advised anglers going after silver carp to be sure to protect their gunwale-mounted throttles from an inbound fish that could send the boat surging out of control.

But he surprised some by saying that even the silver carp are not especially prodigious jumpers compared to other fish, pound for pound; it’s just their sheer size and power that puts their leaps into the record books at 10 feet or higher.

One theory for this behavior, by the way, is that in Chinese rivers their historic predators included 30-foot paddlefish that, unlike their filter-feeding American cousins, came equipped with jaws and teeth like those of a great white shark — and the best escape route was vertical.

  • Chapman’s prepared remarks didn’t deal directly with threats to the Great Lakes from Asian carp, but in answer to an audience question afterward, he said he thought Lakes Michigan and Erie could be vulnerable to serious harm. Lake Superior, on the other hand, might be at less risk because it offers less hospitable conditions.

And to another question, no doubt prompted by his title slide, Chapman explained the plurals of “carp” this way: If you’re talking about two or more individual fish, it’s carp, as in, My Scout troop in Columbia caught 140 carp in 90 minutes. If you’re talking about two or more species, it’s carps: There’s more to know about the bighead, silver, black and grass carps than you get in a typical TV news story.

Now you know.

* * *

Article continues after advertisement

Chapman’s lecture was sponsored by the Freshwater Society along with three units of the University of Minnesota: the College of Biological Sciences, the Minnesota Aquatic Invasive Species Research Center, and the College of Food, Agricultural and Natural Resource Sciences. Video of the full program is available here.

And an interesting update on the situation in rivers branching east of the Mississippi turned up in the Milwaukee Journal Sentinel on Saturday: Advance of Asian carp in western Wisconsin remains slow — for now.