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They can weigh 40 kilograms, eat nearly half their weight each day in plankton, and have been known to bludgeon unsuspecting anglers as they leap from the water.
And if their advance through U.S. waterways isn’t halted, two species of Asian carp could become the next big threat to the already unstable Great Lakes ecosystem and its multimillion-dollar fishery.
Eighteen Canadian officials, most of them from the federal Fisheries Department, have been helping co-ordinate a mass fish slaughter along a Chicago-area canal in a bid to stop the carp’s advance toward Lake Michigan.
Illinois authorities have dumped about 900 kilograms of the fish toxin rotenone into a nine-kilometre stretch of the Chicago Sanitary and Ship Canal.
Last week, officials announced they had found a single immature Asian carp among tens of thousands of dead fish.
“My guess is that if they get in (the Great Lakes) they’ll wreak absolute havoc,” said Peter Meisenheimer, executive director of the Ontario Commercial Fisheries Association.
“They’ll completely change the ecosystem.”
He said the province’s $100-million commercial fishery is at stake.
“The only thing that (Canada) can do is put pressure on the Americans to get their house in order,” he said.
Introduced to North America in the 1970s to stop the spread of algae, the silver and bighead species of Asian carp escaped from southern U.S. fish farms in the 1990s during flooding on the Mississippi River.
Since then, they’ve made inexorable progress towards the Great Lakes, thanks largely to the canal. Completed in 1900, the canal was designed to divert waste from Lake Michigan, Chicago’s water supply. But it also proved to be a fish freeway, letting invasive species move unimpeded from the Mississippi into the lakes.
Two electric barriers went up in 2002 and 2006 to deliver migrating fish a non-lethal jolt and hopefully change their course. But in July, scientists discovered DNA from Asian carp beyond the barrier, suggesting they may already be in Lake Michigan.
When one of the barriers had to go offline for maintenance this past week, authorities gave the go-ahead for the mass kill-off.
Finding one dead Asian carp among tonnes of fish carcasses suggests the invasive species is closer to the Great Lakes than scientists had suspected six months ago, said Becky Cudmore, a science adviser for Fisheries and Oceans Canada.
Cudmore, one of the Canadian scientists overseeing the rotenone poisoning, said that while it’s possible the carp are already in Lake Michigan, the fact only one specimen was found is a good sign.
“Numbers are really low at the front of the invasion, so we are still in an excellent position to be fully in prevention mode,” she said.
Cudmore said there are plans for a third electric barrier to be built along the canal by 2010.
While it’s understandable drastic measures had to be taken, it’s also disturbing the carp have reached so far north, said Krystyn Tully of the Lake Ontario Waterkeeper, a Toronto-based environmental group.
“This is a problem that we’ve seen coming for a decade,” Tully said Friday. “The fact that it’s come to this is extremely frustrating.”
The worry, she said, is that the Asian carp, which has no known predators, could devastate the Great Lakes by wiping out the bottom level of the food chain, leaving existing species with nothing to eat.
Tully said the canal, a vital shipping route, should be closed.
“You can take site-specific measures, but it’s becoming almost impossible to eradicate invasive species once they get here and they become entrenched in the ecosystem,” she said.
One U.S. politician, Michigan Gov. Jennifer Granholm, and five environmental groups have threatened to sue the U.S. Army Corps of Engineers to force the closure of three shipping locks near Chicago that could stop the carp’s advance.
The U.S. federal government confirmed Friday a decision on shutting one lock could come within days.
Two officials with Ontario’s Ministry of Natural Resources were in Illinois to oversee the recent kill.
Natural Resources Minister Donna Cansfield said some reports have suggested the carp won’t be able to reproduce in the Great Lakes, given the difference in lake and river currents.
As well, the fact only one Asian carp has been found beyond the electric barriers might suggest the fish aren’t as pervasive as had been feared, she said.
“Having said all of that . . . keeping them out is of paramount importance.”