Destructive carp invader hits Lake Ontario
Monday, November 24, 2003
The Globe and Mail (Canada) by Martin Mittelstaedt
Biologists have discovered a grass carp, a dangerous invasive fish originally from Eastern Asia, living in Lake Ontario at the mouth of the Don River in Toronto.
The grass carp was caught inadvertently a few weeks ago by staff at Toronto and Region Conservation during an assessment of the size of fish communities in the Lower Don River, one of the city's most polluted waterways.
Grass carp are feared because they are voracious feeders of aquatic vegetation, an attribute that causes serious disruption of any environment in which they become well established. Their most destructive practice is ripping underwater vegetation out by the roots, leading to increased turbidity and poor water quality. They have become a major pest in some areas of the United States, harming the commercial and recreational fishing industry.
The pale grey fish, related to the common goldfish and also known as the white amur, can become uncommonly large, growing up to a metre in length and weighing up to 50 kilograms. It is something of a plant eating machine, consuming up to its own body weight in vegetation each day, giving it huge potential for disrupting underwater plant communities.
Researchers from the Toronto conservation authority made the discovery on Oct. 30 while they were electrofishing -- passing an electric current through water -- to determine the size and composition of the fish community in the Lower Don.
The electric current temporarily stuns all fish in the immediate vicinity and makes them float to the surface. Scientists can then easily gather them up in nets and identify the species and their populations in a given area.
Scientists do not know yet whether the carp they caught is a single fish released into the wild by someone in the city, or if it is part of a previously unknown breeding population around Toronto.
Live carp can be bought in fish markets, through the aquarium trade and even over the Internet.
To try to solve this mystery, Toronto and Region Conservation, the Ministry of Natural Resources and the federal Department of Fisheries and Oceans are conducting what they call an "aggressive" surveillance program on rivers that lead into Lake Ontario to determine if there are any more of the fish.
"The Ministry of Natural Resources is committed to investigating this incident to confirm that this is an isolated instance," Natural Resources Minister David Ramsay said.
As long as the weather remains mild, researchers will be conducting more electrofishing on the Don, Humber and Rouge rivers this year. Additional electrofishing is planned for next spring.
There have been only four known previous sightings of grass carp in Ontario, and all of these were presumed to be solitary individuals and not part of an established breeding population. One fish was caught in Lake Erie in 1985 and three more in commercial fishing nets in southern Lake Huron during 1989 and 1998.
Grass carp were first brought to the United States in the 1960s for research on the control of water plants, but they subsequently escaped the research ponds.
They were introduced in Alberta in 1987 to see whether they could keep irrigation canals clear of vegetation, but they have since escaped into the wild. Many areas in the U.S. and Alberta require that only sterile grass carp be released, but despite this precaution, breeding populations have become established in the U.S.
The fish caught in Toronto is being tested to determine its age and whether it was capable of reproduction.
The Ministry of Natural Resources is asking the public to report any sightings of grass carp, and wants fishermen to keep samples of fish suspected of being grass carp so they can be positively identified.