Will Asian Carp Invade Canada?
A thin, underwater “electric fence” in a canal near Chicago, and vigilance by governments and citizens, are all that prevent a group of invasive fish species from disrupting aquatic ecosystems across the Great Lakes.
Four species of Asian carp, the grass, bighead, silver, and black, could readily move from the United States into Canada. Freshwater fisheries scientist Nick Mandrak, of the Great Lakes Laboratory for Fisheries and Aquatic Sciences (GLLFAS) in Burlington, Ontario, says that “people tend to think of Asian carp as semi-tropical. But I've seen them thriving under a metre of ice in frozen Russian lakes. They could survive right across Canada. And they can do great damage.”
While scoping out the threat to Canadian waters including the Great Lakes, Dr. Mandrak and colleagues in the Department of Fisheries and Oceans and elsewhere are also providing scientific advice to American authorities trying to contain Asian carp. Some species have spread up the Mississippi River system to the Des Plaines River, only 50 miles from Lake Michigan.
People have imported Asian carp to North America for various purposes. Farmers may put grass carp into ponds to clean up unwanted vegetation. Consumers, especially of Asian heritage, use carp for food. And in the United States, fish farmers began raising them on farms next to the lower Mississippi River. The problems came with accidental releases into the wild, in the 1980's and 1990's.
Some Asian carps grow to more than 50 kilograms and longer than a metre, so they're big eaters, causing damage at several levels. The grass carp can destroy native plants in rivers, lakes, and wetlands. All four species when young have large appetites for zooplankton and phytoplankton, and these tiny animal and plant organisms remain major food items for adult bighead and silver carp. The black carp likes mussels and snails. Thus, carp can destabilize the aquatic food chain from nutrients and plankton on up, out-competing other species, and throwing off entire ecosystems.
Potential distribution of grass carp, based on mean annual air temperature range in native distribution. Distribution of black and silver carp would be broadly similar; bighead carp would stay at somewhat lower latitudes.
Too large for most predators to attack, the Asian carps roam and feed to their heart's content. In the lower Mississippi, the grass, bighead, and silver carps have taken over, now making up most of the aquatic biomass. They have devastated sport and commercial fisheries, displacing other species and destroying nets and gear.
Back in 1900, American authorities created a canal linking Lake Michigan to the Mississippi system by way of the Des Plaines and Illinois rivers. The purpose was to flush Chicago's sewage southward, rather than into Lake Michigan, which provided drinking water. Today, the Chicago Sanitary and Ship Canal also provides transport and recreational boating, and officials are reluctant to close it.
In 2002, to keep Asian carp or other species from crossing between the Mississippi system and the Great Lakes, American authorities set up an electrical field in the canal to repel fish. But as Nick Mandrak points out, "a failure of that single barrier would open up the Great Lakes to Asian carp. And invasive species can also enter Canada by other means."
The destructive zebra mussel, for example, probably arrived in the ballast water of a single foreign ship in the 1980's. They have spread through large areas of the Great Lakes, causing billions of dollars in damage. The mussels clump together on wharves and other structures, clog up water systems, and, when ingested, raise toxicity levels in birds and fish.
A more likely route for Asian carp would be the live food-fish trade. Dealers have in the past imported them for Asian-Canadian consumer markets. As well, some religions have ceremonies involving the release of live fish. If unaware of the dangers, practitioners might release Asian carp or other invasive species rather than native fish.
Isolated captures of grass carp have taken place in Lakes Huron, Erie, and Ontario, although there is no evidence of established, self-reproducing populations. (As for bighead carp, one of only two discoveries so far in Canada's "wild" came in a municipal fountain in Toronto, where a buyer discarded a live fish.)
In Alberta, Asian carp brought in to clean out pond vegetation have escaped at least once. No adverse consequences seem to have arisen, since those particular fish came from what are known as "triploid" eggs, treated to prevent reproduction. But even triploid treatment, Nick Mandrak notes, can have less than 100 per cent success.
Dr. Mandrak and colleagues have analyzed Asian carp characteristics to see how each species would survive in fish habitats across Canada. They have determined that once introduced, every variety would have a high chance of establishing itself. There appears to be no threat of interbreeding; the carps are too different genetically to create hybrids with native species. The damage would come from other effects, as in the Mississippi. Asian carp would distort the entire aquatic food web, to the vast detriment of existing fishes. On top of that, they can provide a pathway for new parasites and diseases.
Different types of carp would seek different habitats. The grass carp would go for wetlands and other vegetated areas. The others would cruise further offshore, eating plankton or other fish, with black carp dining especially on mussels. But there's no hope of it taking on the zebra mussels, which clump closely together and are difficult for predators, such as the black carp, to consume. Instead, black carp would go after native mussels, many of which are already classified as endangered.
In the Great Lakes, familiar species such as yellow perch, walleye, and cisco could all suffer. And Asian carp could survive in rivers and lakes of every province, with some reaching the Territories and Alaska.
Dr. Mandrak and research colleagues are fine-tuning their predictive models and their estimates of where, how, and how fast the Asian carp would spread. But what about coping with them once they arrive?
"If they get established, there's little you can do," Dr. Mandrak says. "In the case of sea lamprey, an alien species of long standing, scientists found a lampricide that keeps them under control. But for Asian carp, the only hope seems to be keeping them out."
Ontario in 2005 passed regulations forbidding the sale or possession of Asian carp, along with snakeheads and gobies. And the Department of Fisheries and Oceans is working with other federal and provincial agencies towards a national plan to combat invasive species. The proposed approach will stress research, awareness, co-operation and co-ordination, and above all, prevention.
"We've done our best to assess the risks from Asian carp, and they're major," Nick Mandrak says. "Now it'll take major vigilance to keep them out of Canadian waters."
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