Undercurrents: beneath the obvious

November 28, 2006

Great Lakes Vulnerable As Asian Carp Overwhelm Nearby Rivers

Filed under: Invasive Species — nemo @ 6:53 pm

RedOrbit carries this report of the rapid advance and threat posed by Asian Carp. 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 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.

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.

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.”

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.

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.

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