Now that a leaping silver carp and its kissin' cousin, a bighead carp, turned up in a commercial fisherman's net near Winona, Minn., sportsmen, environmentalists, scientists and politicians of all ideological stripes are boarding the Stop Aquatic Invasives bandwagon.

Members of Minnesota's congressional delegation introduced a bill for Upper Mississippi Conservation and River Protection (CARP, naturally) to close the lock and dam at St. Anthony Falls if Asian carp are found north of Hastings.

The legislation would tap into a $50 million federal fund for controlling the spread of Asian carp. (These fish, by the way, are not closely related to the common carp, widespread in Minnesota waters for a century.)

On a state level, legislators are moving a bill to spend more money in the fight against Asian carp, zebra mussels, and other exotic species -- that is, species of plants and animals introduced from somewhere else. Legislators are considering spending $13 million to install electric fish barriers and $16 million in bonding to make the Coon Rapids Dam carp-proof.

Some lakeshore residents want money from the Clean Water Legacy fund to fight zebra mussels. There is also a proposal to tap the fund for $1.8 million (with more money coming from bonding and the lottery) to start up an aquatic invasive species research center at the University of Minnesota. Peter W. Sorensen, the fisheries professor who proposed the center, says it's time to declare "war" on aquatic exotic species.

So war it is. But here are a few things to keep in mind. Because as Mark Davis, chairman of the biology department at Macalester College and author of the scientific text "Invasion Biology," recently told me, "A lot of money has been made by amping up the fears of invasive species."

The bad news: This is really hard

Biology is really tough to control. We don't have nearly as much dominion as we'd like to believe. Options for controlling uninvited plants and animals often come at great cost to our prosperity, enjoyment and freedom.

Exotic species move through trade, travel and tourism. People move; organisms follow, from pathological viruses to forest pests to aquatic weeds. Humans are unwilling to give up trade and travel (and the prosperity that comes from them) to stem the spread of deadly disease. What are the chances we will curtail our travel to prevent the spread of carp and buckthorn?

In Minnesota, the most effective and immediate way to cap the spread of zebra mussels? Easy. Close the public access we've spent decades and millions of dollars to develop. Peter Sorensen argues we should consider returning to a day when we rented boats at the lakes where we vacation.

I, for one, live for each new opportunity to carry my canoe to a different stream or lake. I would be loathe to give that up. And I suspect a lot of others feel the same way about the freedom to travel with their own boats.

Even nature works against us in the spread of exotics. In a paper published recently in PLoS One, Netherlands Institute of Ecology biologist Casper van Leeuwen demonstrated that some species of small snails can survive a trip through the intestinal tracts of mallards and, in theory at least, hitch a ride to waters hundreds of miles away.

Our largely successful fight against sea lampreys in the Great Lakes during the last half century hinged on two things: First, control was worth the money and effort because lampreys were causing very expensive damage by preying on lake trout, a popular sport and food fish.

Second, lampreys were uniquely vulnerable when they gathered in small tributaries to spawn. Many other species of aquatic invasive species show no such vulnerabilities and can probably never be controlled, much less eradicated.

The good news: It's not as bad as it seems

Despite our fears, exotic species will not, as many fear, "destroy the ecosystem."

Some diseases and agricultural and forestry pests are scary indeed. Who wouldn't want to bar the door against avian flu and emerald ash borer?

But other species, even ones that make our skin crawl, not so much. The dreaded silver and bighead carp, for example, have left an ambiguous body of evidence in the Mississippi and Illinois rivers.

Kevin Irons, aquatic nuisance species program manager for the Illinois DNR, reports that the carp, which strain the water for tiny plankton, present stiff competition for native bigmouth buffalo fish and American gizzard shad.

But there's no evidence they wiped out anything, or even caused the decline of any game fish. "I don't believe we've lost any species," he says.

In fact, the ascendance of Asian carp in the last decade has doubled Illinois' commercial fishing harvest.

"That's our primary business," said Jesse Schafer, of Schafer Fisheries in Illinois. "We harvest millions of pounds of them a year."

Most are shipped to the coasts and to Asia. Commercial fishermen are taking so many Asian carp that Schafer sees the size and abundance of fish dropping.

"You can't get rid of them, but you can overharvest them," he says.

Meanwhile, commercial fishermen continue to net the native buffalo fish and sheepshead.

"I don't think the Asian carp have really affected them too much," says Schafer. "It seems some of the game fish are actually more plentiful because they're eating the Asian carp eggs and small fish. The bass are having a smorgasbord. It's the same with the catfish, too. Mother nature's taking care of itself."

Anecdotal? Sure. But it does suggest the sky hasn't fallen.

Do no harm

Carp-phobia has created a psychology of walls and fences. Just as we've built a wall along the Mexican border to keep out alien humans, politicians and citizens are clamoring to build bubble barriers and restore dams on major rivers to prevent the spread of alien aquatic species.

But building bulkheads does no favors for the environment, especially our fisheries. Recently, we have removed dilapidated dams on streams such as the Kettle and Cannon to allow fish to move freely over dozens of miles of stream -- a real boon to game-fish populations. DNR fisheries biologist Luther Aadland has made a career of creating fish passageways around stream-choking dams to "reconnect" hundreds of miles of waterways.

It would be a shame to stymie or undo this beneficial work for the sake of a carp crusade. Says Aadland, "Dams are the biggest cause of extinction and extirpation of native species, while reservoirs and the altered habitat associated with dams are the biggest propagators of nonnative invasive species."

Science, not advocacy

If Sorensen succeeds in establishing an invasive-species research center at the university, "the idea would be to bring some focus to issues in Minnesota," he recently told me, "to develop new tools to solve invasive-species issues in Minnesota. The idea is to be as flexible and imaginative as possible."

Indeed, when it comes to exotic species, there are plenty of interesting and important research questions.

On the level of basic research: Are exotic species suitable substitutes for native species to provide "ecosystem services," such as wildlife habitat, carbon sequestration, erosion control or pollution reduction?

Do new species increase biodiversity or subtract from it? Is local diversity (by, for example, the introduction of new species) a valuable thing? Does it outweigh the loss of diversity at the global level (if, for example, endemic species go extinct)? Are species introduced by the hand of humans quantitatively distinguishable from species that arrive by "natural" means?

The opportunities for applied science are likewise interesting. In fact, Sorenson has worked on many of them.

Is there something in the life cycle or behavior of a nuisance such as common carp that makes it vulnerable to control or capture? Can the signature chemical pheromones emitted by fish be used to control or eradicate nuisance species?

Can exotic species be suppressed through the introduction of other exotics? How can we predict which species will become nuisances and which will not?

These are questions worth pursuing. But they are a far cry from the "war" on invasive species that Sorensen has also recommended. That promises to be as much a bargain as a war on drugs or a war on terror.

It's the habitat, stupid

One of the wisest observations on the exotic species scare comes from an unexpected source, Banu Subramaniam, an associate professor of women's studies at the University of Massachusetts. She's struck by the militaristic and "xenophobic rhetoric" that blames "aliens" for problems of our own making, distorting our view and even our management.

"The solution becomes stopping these alien species and focusing on them rather than on things such as development and what we are doing about habitat," Subramaniam told me. Blaming exotics "adds to the hysteria without doing anything that is actually going to help."

Waterfowl haven't declined because of carp. Wetlands haven't disappeared because of purple loosestrife. Bald eagles weren't once imperiled because of English sparrows. And moose aren't dying off in northern Minnesota because of buckthorn. If anything is "destroying ecosystems," it is the usual cast of villains -- pollution of air and water, destruction of habitat, poor land management.

So when it comes time to apportion Legacy grants or appropriate state and federal funds, sure, devote some to research and control of invasive species. But realize the best use of money, time and labor for a better natural world is restoration of natural habitat, clean water and clean air.

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Greg Breining, of St. Paul, writes about science, nature and travel. He is the author of "Paddle North: Canoeing the Boundary Waters-Quetico Wilderness" and "Wild Shore: Exploring Lake Superior by Kayak."