Monstrous Leaping Fish Are About to Invade the Great Lakes. Here’s How to Stop Them.

Slate’s animal blog.
Nov. 18 2013 12:49 PM

How to Stop an Invasion of the Easiest Fish in the World to Catch

An Asian carp leaps into the air.
An Asian carp leaps into the air after being spooked on the Illinois River in Peoria, Ill.

Photo by Mira Oberman/AFP/Getty Images

I leaned over the bow of a speeding boat with a long-handled net in my hands. The muddy water of a tributary of the Missouri River splashed my face. A fat, silver fish, as long as my arm, leapt out of the water as I lunged for it with the net. I missed, but it didn’t matter. The fish launched straight over my head and into the boat’s deep metal bin made to hold the catch of the day.

This was the easiest fish I ever caught in my life, but it wasn’t exceptional.  A dozen more voluntarily followed it into the boat without any encouragement on the part of yours truly.


These fish were silver carp, an invasive species from Asia that has been trashing ecosystems and fisheries throughout the Missouri and Mississippi river systems. Reaching up the Illinois and Des Plaines rivers to only a short distance from Lake Michigan, the species is considered the No. 1 threat to the Great Lakes if it manages to get in. More than $200 million has been budgeted to prevent it from entering the Great Lakes. But perhaps the real question should be why there has been so much hand-wringing over what to do about a fish that literally jumps into fishing boats.

The silver carp was deliberately brought to the United States during the 1970s to help clean up pollution in fish farms. They weren’t expected to escape, and at the time it was believed that the fish couldn’t successfully reproduce in American waters. As it happened, silver carp can make it just fine in the wild.

The carp’s advantage is in its method of eating. While it is capable of feeding conventionally through its mouth, every silver carp also has sponge-like pads on its gills that filter out tiny zooplankton and phytoplankton and use this material as food. The principle is similar to feeding in baleen whales. Every time this fish breathes, it eats. When water is polluted with excessive phosphates and organic material, that pollution helps plankton thrive, and the carp eat the plankton.

Baby silver carp hide in thick cover and grow bigger and bigger until there isn’t anything around except for a bald eagle that could even consider tackling them. Carp weighing 50 pounds are not unusual on the Missouri River.

Because they eat so low on the food chain, silver carp disrupt the food supply of everything else in the water. The total biomass of some stretches of river now consists of up to 95 percent invasive carp.

The Army Corps of Engineers constructed a set of electronic barriers to keep carp from migrating up a canal and into Lake Michigan. An electric current zaps and kills any fish that try to swim through it. Close to $200 million has already been spent on this system of barriers. But could it be a waste of money in the long run?

The problem with the barriers is that they may stop fish, but they cannot prevent human intervention. Fishermen catch live bait constantly using nets and minnow traps. Very small silver carp look like many other baitfish to the untrained eye. All it will take is one uninformed fisherman putting a bait bucket containing some silver carp in the back of his truck or bass boat and moving from one fishing spot on the Des Plaines River to another spot on Lake Michigan. With these waterways only a few miles apart in some places, it is only a matter of time until an accidental human introduction occurs. Once this happens, that $200 million will go right down the drain.

Meanwhile, next to nothing has been spent on eradication of silver carp in areas where they have become established. This is perplexing because silver carp are arguably the easiest fish to catch in North America. A genetic quirk of the population introduced to America is that they react to the sound (or perhaps the electromagnetic signature) of a motor by leaping madly into the air.

The most rational response to the invasion of silver carp would probably be to drag nets through the water and catch them while releasing native fish. This is literally stone-age technology. The operation should be able to pay for itself by selling the fish as food. It wouldn’t eliminate the baby fish, but at least it would lessen the ecosystem damage from adult fish.

The flesh of the silver carp is quite palatable. I have cooked and eaten silver carp and can testify that when they are promptly cleaned and processed, they taste like any other firm white fish. In a blind taste test, most people would not be able to distinguish between carp and cod. But in today’s market, we don’t even have to worry about whether people are willing to try eating something labeled “carp.”

Walk into the frozen food section of any grocery store and look at the fish filets and fish sticks. Most of the packages don’t say what species of fish it is. They could contain anything from guppies to goldfish and we wouldn’t know the difference.

I spent some time discussing this with Phillippe Parola, a Parisian chef who has been cooking for decades in Baton Rouge, La. As we hunted and cooked another invasive species (nutria, a delicious giant rodent), he described his efforts to get federal approval to market carp under the label “silver fin.” Sort of like how Patagonian toothfish was rebranded into “Chilean sea bass.” Parola’s labeling has been approved. The trouble is that there is still no network of local processing plants near the Missouri River capable of processing silver carp into the types of food products that the American market will buy. Carp have unusual bone structure compared with most other fish, and they require different technology to process.

What if, instead of spending hundreds of millions of dollars on barriers that will eventually be circumvented, we spend 10 percent of that money on a few processing plants? With a market that would pay 25 cents or more per pound, commercial fishermen would be able to make a reasonable living ridding the water of silver carp. When the fish finally start to take over the Great Lakes—it’s just a matter of time—build more processing plants.

This approach would probably never completely eliminate silver carp in the United States. But it can keep them controlled to a point where they don’t pose such a serious threat to ecosystems or economies.

Meanwhile, the last hope for natural control of silver carp in the Great Lakes has recently been dashed. It had been thought that carp would not be able to successfully reproduce in lakes. Carp eggs need to float down many miles of moving water without sinking or they don’t develop. Four invasive grass carp were recently found in a tributary of Lake Erie. Analysis of the fish determined that they had been born in the wild. Because grass carp have basically the same spawning needs as silver carp, it looks like silver carp will have the run of the place once they get into the lakes.

If $200 million worth of high-tech hardware won’t keep carp from moving into the Great Lakes, then maybe it’s time to find out if some stone-age know-how can get them out.


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