Unwanted bounty
Written by Milwaukee journal Sentinel   
Wednesday, 18 October 2006 05:22

The only thing more spectacular than the volume of Asian carp now frothing the water in some river stretches of the northern Mississippi basin is the speed at which the invasion has occurred.

Part-time commercial fisherman Mike Savochka netted 6,500 pounds of bighead carp on a hot summer morning in late July. He said those nets, dropped in the same area of the Illinois River, once regularly filled with 5,000 pounds of native buffalo fish.
"Today we got one," he said of his buffalo fish total. "Not 1,000 pounds. One fish."

Savochka remembers the first bighead he brought into his wholesaler. Nobody knew what it was.

"We thought they were salmon," he said.

That was just five years ago.

Four species of Asian carp are now loose in U.S. waters. The most menacing - bighead and silver carp - have overwhelmed stretches of river in the Mississippi basin and have been found within about 50 miles of the shoreline of Lake Michigan. Imported as an agent to clean fouled waters, the filter-feeders let loose by government researchers three decades ago have a new generation of biologists in a fight they fret they cannot win.

It is a fight that could well change forever life in the Great Lakes region, home to more than 4 million recreational boats and a $4.5 billion annual commercial and recreational fishing industry.

Caught off-guard by the blitzkrieg speed of the invasion, researchers have yet to figure out exactly how the fish are affecting the Mississippi basin's native species. But those who make their livings studying the infested rivers say there is little doubt that these creatures that are so effective at stripping the plankton at the bottom of the food chain are changing the way things work in the river.

Bighead carp can reach a jockey-sized 100 pounds; the jumping silver carp are just a slightly smaller version of the bighead. Neither has a true stomach, which essentially compels them to eat non-stop. One fish can carry as many as 5 million eggs, a devastating attribute if the fish get into waters where no worthy predators exist.

"Their strategy," said United States Geological Survey biologist Duane Chapman, "is to overwhelm the environment."

Kevin Irons, a biologist with the Illinois Natural History Survey in the Illinois River town of Havana, has watched that strategy succeed.

"Six years ago, the Asian carp was nothing," Irons said. "Now most of the biomass out there is bighead and silver carp, so there certainly are implications."

But Carole Engle, director of the aquaculture center at the University of Arkansas at Pine Bluff, points out that silver and bighead carp have been swimming in the wild in Southern states for more than two decades, yet they apparently have not reproduced nearly to the extent that they have in Northern waters. She thinks polluted Northern rivers are a big part of the problem.

"There are tremendous amounts of nutrients going into that (Illinois) river," she said.

That, she said, means there might be plenty of food to go around for all the fish, and she notes that the scientific community has yet to show a direct connection between the silver and bighead carp explosion and the loss of native species on an ecosystem already ravaged by pollution, dams and other invasive species. She said "hysteria" has taken over where hard facts are needed.

"We need good science," she said, noting that heavy infestations on the Illinois, Mississippi and Missouri rivers appear to be localized and not uniform throughout the basin. "What impact are these fish really having?"

Geological Survey biologist Cindy Kolar agrees that the data on the Asian carp's impact on native species are slim, but that doesn't mean there isn't trouble in the water.

"In terms of (scientific) literature, it's just not there yet," she said. "That doesn't mean there are not effects."

Illinois biologist Irons points to preliminary results from a study on an 80-mile stretch of the Illinois River that shows the average weight for a 25-inch buffalo fish has dropped from over 12 pounds to less than 9 pounds in the last five years - a period of time that coincides with the invasion.

"We're seeing the buffalo are starting to suffer," agreed Rob Maher, commercial fishing program manager for the State of Illinois.

Maher adds that he is seeing commercial fishing operations go belly-up across the state, and a big reason is that the only thing fishermen are finding in their nets is thousands of pounds of unwanted fish.

The recreational fishery is also suffering.

Mike Conlin, chief of fisheries for the Illinois Department of Natural Resources, said he has seen enough to know there is "no question" the carp have squeezed out the native bass on the Illinois River near Peoria - and the anglers who chased them. He notes that Peoria's big-time bass fishing tournaments have disappeared in the last decade and said they are "absolutely" a casualty of the bighead and silver carp invasion.

Today the big sport in Peoria is watching the silver carp jump. Or slaughtering them with bow and arrow.

"We're trying to take advantage of a bad situation," said Christine Apple- berg, president of the Illinois Bowfishers association.


Biologists concede that they have yet to find a way to halt or even slow the spread, and every section of river or lake the fish colonize is likely a section of river or lake that will have Asian carp for good.

Some people are hopeful that strategic fishing programs might someday help curb the Asian carp numbers, but at the moment the price is too low to bring enough fishermen to the river.

There is a downside to relying on fishermen to control the species - inevitably the fishermen will become dependent on them. That could lead to demands that biologists manage waterways to sustain carp numbers in order to sustain the fishing industry, and "I certainly don't want to be managing rivers for these fish 20 years from now," said Geological Survey biologist Chapman.

Another potential control is to plant native predators, but the carp grow so fast - twice as fast as other fast-growing Mississippi natives, such as the gizzard shad - that there are worries no native species may be able to control them.

"Once you get to be a 5-kilogram (11-pound) silver carp, there's not much out there that is going to bother you - other than people," said Chapman.

The extensive dam systems on the rivers of the Mississippi basin could also be used to manipulate the peak spring flows that spawning Asian carp apparently require.

There are wilder ideas.

Researchers are beginning to look at genetically modifying captive fish so they produce only male offspring. The theory: Release these fish into the wild, and they might just eventually - and ironically - breed themselves into extinction.

Fish poisons such as rotenone, meanwhile, are out of the question except for small-scale treatments because of the number of fish and the vastness of waters they have infested.

So the question now is: Where will the fish will turn up next?

"In invasion biology, proximity to the source is probably the single most important predictor," said Gregg Sass, director of the Illinois Natural History Survey research center in Havana, Ill.

That means the Great Lakes are in trouble.


The only thing standing between the fish and the Great Lakes is an electric barrier on the Chicago Sanitary and Ship Canal that has a history of power failures.

The Great Lakes are already ravaged by the arrival of more than 180 foreign invaders, and the worry is that the carp could be disastrous for an already sick system.

Although the lakes still sustain a booming commercial and recreational fishery, in some ways the world's largest freshwater system has become more an artificial fish factory than a self-sustaining ecosystem.

The sea lamprey invasion in the middle of the 20th century destroyed what was left of Lake Michigan's overfished native lake trout, the natural king of the food chain. The loss of that top predator opened the door to invading alewives, a pocket-comb-sized Atlantic herring that, coupled with historical overfishing, decimated what was left of Lake Michigan's other native species.

Today, lampreys are controlled by a non-stop poisoning program, and alewives are controlled by a non-stop Pacific salmon-planting program, which drives the lake's recreational fishing business.

Native species have been eliminated or so squeezed to the side that the entire system is now, in the words of renowned Canadian biologist Henry Regier, "stripped down to just a very simple and sad caricature" of its former self.

That makes it particularly vulnerable to new invasions. Picture today's "stripped down" version of the Great Lakes food chain as a skinny tower of building blocks, instead of the fat pyramid it once was. Now imagine the comparative damage that could be done by pulling a block from the base.

"The more complex an ecosystem is," explained Ron Benjamin, Mississippi River fisheries supervisor for the Wisconsin Department of Natural Resources, "the more resilient it is."

The system is already showing signs of wobbling.

In the late 1980s, the average 7-year-old native whitefish in Lake Michigan weighed more than 5 pounds. Today a fish that same age weighs about 1.5 pounds. The reason: The whitefish's main food source, a tiny shrimp-like creature, is disappearing from the lake bottom, a likely consequence of the arrival of the filter-feeding zebra mussel in the late 1980s and its cousin the quagga mussel a decade later.

But the trouble they're causing should worry more than fishermen.

The filter-feeding mollusks have also increased water clarity, which has spawned outbreaks of rotting algae, at times rendering Lake Michigan beaches useless and producing a stink so wretched it does what was unthinkable just a few decades ago - it can make you pity the people who live in the million-dollar mansions on the lake bluffs.

There are more ominous impacts; in some places on the Great Lakes, mussel-induced algae blooms have triggered botulism outbreaks that have killed tens of thousands of birds.

Zebra mussels have also been implicated in increased levels of a toxic blue-green algae called Microcystis, which produces a poison that can cause liver damage.

And now there is the looming arrival of filter-feeding Asian carp, dubbed by some the 100-pound zebra mussel and, biologist Chapman notes, another Microcystis-enhancing species. Microcystis is covered with a material that allows it to survive a trip through a silver carp's nutrient-rich gut, and it actually "comes out on the other end stimulated," Chapman said.

The question on everybody's mind: Can the Asian carp find a home in the Great Lakes?

The unfortunate answer: Yes.

Chinese professor Zhitang Yu has studied Asian carp for 50 years and probably knows as much about the habits and needs of the fish as anyone in the world. He thinks our big lakes would be a suitable home, even if they are colder and clearer than the nutrient-rich rivers of the Mississippi River basin. That, he said, means only that the fish will grow at a slower rate.

"In northern China, it's very cold, and we have the fish there, too," Yu said through an interpreter.

The Great Lakes tributaries, he said, will be the biggest trouble spots.

Chapman agrees adult Asian carp might find a home in the lakes, but the fish need the lakes' big, free-flowing tributaries to spawn. Biologists have mapped 22 such rivers on the U.S. side of the Great Lakes, including the Manitowoc and Sheboygan rivers.

Most also agree Asian carp could thrive in the warm, shallow bays and harbors of the Great Lakes. Unfortunately, those are the same waters anglers and boaters tend to occupy, as well.

What worries U.S. Fish and Wildlife Service biologist Mike Hoff is that the Great Lakes are being compared to other lakes and reservoirs, and they shouldn't be.

"The Great Lakes are, in some places, much like rivers. There are big, strong currents," he said. That could make open waters suitable spawning grounds, and that, he said, "unlocks much more habitat."

Hoff also worries what the combination of all five carp species could do to the lakes, because they depend on such different types of food. Bighead and silver carp are filter feeders; grass carp eat vegetation; and black carp eat mollusks. And then there is the bottom-foraging common carp, a weed-of-a-species that has plagued the Great Lakes for more than a century.

Each individually poses a significant threat, but Hoff said that working together they "can break apart the connections on which our ecosystems are based."

The only prediction Chapman will make about how the fish could change the lakes - and the way people use them - is to "expect the unexpected."

"It's possible you could drift along for 40 years before they go crazy. Or they could go crazy right away," he said. "You can't predict it."

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