Asian carp, from mouth to tail

“Asian carp” is an umbrella term that refers to a half-dozen species of fish. But two have made national news in recent years — bighead carp, which can reach 100 pounds in their native Asia and better than 40 in the United States, and silver carp, which are about half that size.

These two have taken over large parts of the Mississippi and Illinois River systems and threaten to invade the Great Lakes. The silver carp’s habit of exploding from the water by the dozens to evade predators or boats has earned it a lot of TV news time.

All Asian carp belong to a family of more than 2,000 species called cyprinids, or minnows, whose members range from a half-inch to nine feet long. Bigheads and silvers, which look similar, were brought to the United States in the 1970s by Southern fish farmers to clean algae from aquaculture ponds. The carp open and close their mouths constantly as they swim and suck in about 10 to 20 percent of their weight in tiny zooplankton and algae a day.

Black carp, which look very different from bigheads and silvers, were imported at about the same time to eat snails that were carriers for diseases in commercial fish farms, and a fourth species, grass carp, were deliberately introduced into the wild in some states to control aquatic weeds.

Many fish farms were sited along the Mississippi River in Arkansas and Mississippi, and when the Mississippi flooded its banks it sometimes inundated the ponds and let bighead, silver and black carp swim into the river.

Bighead and silver carp spread explosively up the Mississippi and Illinois rivers, which proved so congenial that by the 1990s the carp comprised 90 percent of the fish biomass in many areas, and greatly reduced populations of commercially valuable species like common carp and buffalo fish. Black carp haven’t spread as much, probably because of limited food and habitat.

A fish tale

Many people seem to misunderstand how Asian carp threaten other species in the Great Lakes. A few weeks ago, one of the talking heads on a national news program read a story about the danger posed to the lakes by “ravenous Asian carp” that “would indiscriminately destroy other fish.” That kind of ignorance might help viewers stay tuned until after the commercial break, but doesn’t it help them understand what this is all about.

Asian carp are “ravenous” only in the sense that they suck huge amounts of tiny creatures and vegetable matter out of the water. They are filter feeders, like monstrous zebra mussels, and 99.9 percent of their diet is plankton and algae less than a half-inch long.

The danger is that removing so much plankton from the water steals food from much smaller native creatures that form the bottom links of the food chain. That’s what happened in Lake Huron, where the salmon fishery collapsed from the bottom up about 10 years ago after invasive zebra and quagga mussels sucked up massive amounts of nutrients.

Credit: Sierra Club Illinois

Energy that once went into creating the flesh of native marine life was now locked up on the bottom of the lake in the form of incalculable billions of tiny mussel shells.

Asian carp are not predators; they don’t present a direct physical threat to the bass, walleyes, salmon and perch that anglers target. They don’t present a direct threat even to most of the smaller fish that game fish eat. Instead, they consume the minuscule things that feed the tiny things that feed the small things that these gamefish eat.

But the walleyes that people like to catch aren’t born at 20 inches, or the salmon 20 pounds. Those fish start as tiny hatchlings. Asian carp eat the same food that those hatchlings need to get through the first few days of life, and food that nourishes the tiny creatures the hatchlings will eat when they become fingerling.

Because they are planktonic filter feeders, bighead and silver carp can’t be caught by conventional hook-and-line. They are a major aquaculture species in Asian countries (Laos and Iran are the biggest exporters), and while their flesh is good they haven’t been accepted for consumption in the United States, with the exception of a few cities with large Asian populations.

Some efforts are being made to develop a market in China for Asian carp from the Illinois River (exporters say that Chinese consumers consider wild-caught fish from America to be superior to farmed fish.) But the Chinese want only bighead carp, and shipping costs are high.

Another species often lumped as Asian carp is the common carp, indigenous from the Danube Valley in Europe to southern China. This fish is another example of bungling by government agencies that didn’t understand the consequences of their decisions.

Common carp were introduced deliberately to America by U.S. Fish Commission, the predecessor of today’s U.S. Fish and Wildlife Service (the Romans introduced common carp as far east as Great Britain nearly 2,000 years ago.)

Native fish populations in the eastern U.S. had been so reduced by dams, pollution and overfishing that the Fish Commission sought species to replace them. It settled on two from Europe — common carp, a popular food fish in Germany and Eastern Europe, for warmer waters, and brown trout to replace decimated native brook trout in cold waters.

The brown trout were heartily disliked at first by fly anglers, because they were much harder to catch, but they spread into an environmental vacuum and were soon revered as fishermen learned new flies and techniques to catch them.

Common carp were greatly admired at first and within 20 years had been stocked from coast to coast. But unlike brown trout, common carp compete with every native species from minnows on up, and when a pond was depleted of the crustaceans and insects that were their preferred food, they happily switched to vegetation and turned once-clear waters into mud pits.

Ironically, while today’s fisheries scientists are working to eliminate common carp from our waters, in the past couple of decades the fish has developed a growing following of American anglers who have learned the specialized European techniques needed to consistently catch the hard-fighting species, which often exceed 20 pounds.

The St. Lawrence River, which carries the water of the Great Lakes to the Atlantic Ocean, is generally acknowledged to have the best common carp fishing in the world, and fishing lodges there now draw European anglers who pay $1,000 a week to catch more 20-pound carp in a day than they could expect in a lifetime at home.

In Michigan, several fly fishing guides on northern Lake Michigan and Huron offer sight-fishing for carp in crystal-clear waters, much like sight fishing for bonefish in tropical seas. And the Saginaw River offers excellent carp fishing for anglers who have adopted European bait-fishing techniques.

The sixth “Asian carp” is so closely-related to common carp that they can hybridize, and its numbers have increased remarkably in the Great Lakes watershed in recent years — the goldfish.

Apparently, some owners were too kind-hearted to kill fish they no longer wanted, or some fish survived the ordeal of a toilet flush, and they are now found in rivers and lakes across the country.

Most wild goldfish soon lose their gaudy aquarium colors, revert to the gray-and-silver of their feral ancestors and grow surprisingly large. But a few years ago I was kayak fishing off the south shore of Pelee Island in Lake Erie when I saw some flashes of color among the underwater rocks.

I cast a caddis nymph fly, got an immediate take and soon landed a goldfish as shiny as a rapper’s necklace that went about 2 1/2 pounds. Fought pretty hard, too.

Eric Sharp worked for 48 years as a reporter for the Buffalo Evening News, The Associated Press, The Miami Herald, The Detroit Free Press and numerous magazines, mostly writing about environmental and outdoors issues before officially retiring from the Free Press in 2012. He now splits his year between Florida, Michigan and western New York State where he continues to write about the same issues and is completing a book about environmental changes in the Great Lakes.