Experts disagree on what constitutes an invasion
from the Free Press 1/26/10 :
Do Asian carp really spell doom for the Great Lakes?
Many experts say the future looks grim, since the fish are voracious breeders and feeders that can multiply and scoop up all the plankton other fish need to survive.
Anglers and boaters fear them because one species, silver carp, typically weighs more than a bowling ball and can come flying into boats, injuring humans. The fish have no predators in the animal world, and they appear to have accomplished that over generations by growing too big for predators to eat.
But others say the likely harm from Asian carp depends on how many get into the Great Lakes, and whether they'll find the right conditions to survive and reproduce. Keeping those numbers low is the new mission.
"A few fish getting into Lake Michigan doesn't mean there's a population there," said Duane Chapman, a leading Asian carp expert with the U.S. Geological Survey in Missouri. "This game is not over. It's the numbers that invade the lakes that will ultimately determine whether they have a chance to get established."
Chapman, a U.S. Fish and Wildlife Service official, said last week that hundreds of fish would need to show up in the Great Lakes before he would be seriously concerned.
Earlier this month, carp DNA was found in Lake Michigan, but as yet, no one has found live Asian carp.
A few Asian carp have been found in Lake Erie since 1995, probably released live by humans, but there is no evidence they reproduced, Chapman said.
Even at a large lake in Hungary where Asian carp are stocked, with conditions similar to the Great Lakes, there's no evidence that they have reproduced, Chapman said. But they have reproduced in lakes and reservoirs in Asia.
Food supply low
David Jude, a University of Michigan fish biologist who was the first to find invasive round gobies in the Great Lakes in 1990, said he includes Asian carp in a talk he gives about what could doom the Great Lakes.
But he said there's no guarantee that the fish will find Lake Michigan hospitable. Asian carp feed on tiny plankton, and there's less of it in Lakes Michigan and Huron than there was before quagga and zebra mussels invaded and filtered much of it out of the water.
"The food supply in Lake Michigan is as low as it has been in 40 to 50 years," Jude said.
Lakes Michigan and Huron these days look more like pristine Lake Superior, with water so clear it almost looks distilled, he said. "It's a dramatic change."
Carp that make their way to Lake Erie would have an easier time finding food there, he said. They'll also probably find food in polluted harbors around Chicago, so they might not venture much further, he said.
Another barrier is that while Asian carp tolerate cold, it's not ideal for them, and Lake Michigan might be too cool. Lake Erie, however, is warmer.
The fish also need fast, long rivers to spawn in, and many rivers around the lake are too short to satisfy that need. The fishes' eggs need to be suspended for two days to survive; if they sink in slow water, they die.
Still, there are rivers that could work, such as the Grand River near Grand Haven, Jude said. The Fox and Maumee rivers in Wisconsin and Ohio also would be suitable.
Chapman and Jude said Asian carp could surprise the experts, finding ways to adapt to the Great Lakes.
It's also possible that more are already in the lakes than scientists realize.
Phil Moy, a Wisconsin fish biologist with Wisconsin Sea Grant, said Asian carp could have gotten past the electric barrier in the Chicago shipping canal in October 2008, when it was down for maintenance. That was before DNA testing showed how close the fish were to the barrier.
"They've probably been past the barrier and the O'Brien lock for 14 months now," Moy said.
Prevention is the most important weapon against invasive species, said Marc Gaden, spokesman for the Great Lakes Fishery Commission, set up to conquer sea lamprey, which wrecked the Great Lakes fishery in the 1950s.
"When that fails, the history of invasive species has taught us you don't have many options," Gaden said. "What we're missing now is a directive from the government that's equal to the push to put a man on the moon."
Stopping the spread
Two weeks ago, federal officials laid out how they hope to stop the further spread of Asian carp.
They plan to build an extra electric barrier in the shipping canal as a backup, do electrofishing and netting to capture any carp that might be in or near Lake Michigan, do more DNA testing to see where else carp might be, and try to seal off places where carp can get beyond the barrier.
They are to study whether to close the Chicago shipping canal linking the Mississippi River to the Great Lakes, which barge operators and Illinois politicians strongly oppose.
But federal officials said the latest carp DNA findings don't spell catastrophe.
Jennifer Nalbone, who works on invasive species issues with Great Lakes United, said she hates to hear people say that. Citizens and politicians need to keep up the pressure for action, she said.
"There's a whole lot to be done, and it should be done a heck of a lot faster," Nalbone said. "We can get hold of this, but the question is whether we have the willingness to do so."
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