Why the discovery of a grass carp in the St. Lawrence River concerns experts

Biologists are concerned about the discovery of an invasive grass carp in the St. Lawrence River, and are now struggling to determine its origins.

Last month, twofishermen in Quebec'sLanaudireregion reeled in the 29-kilogram specimen.

Thefish is native to east Asia, buthas been used in North America as a way tomanageaquatic vegetation and is viewed by someas a culinary delicacy.

Ifit manages to reproduce in the St. Lawrence River or the Great Lakes, it could be a major problem for local fish and vegetation.

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That's why the Quebec government decided to fasttrack its plan to fight the invasive species in the wake of the fishermen's finding.

The ministry will spend$1.7 million over three years to try and detect the Asian carp in the river and educate commercial fishermen.

"A grass carp is one of the four or five species of Asian carp that we do not want to see in the Great Lakes or the St. Lawrence," AnthonyRicciardi, an invasive species biologist atMcGillUniversity, told CBC Montreal'sHomerun.

Grass carp have been in North America since the1960sand were brought in to the United States on purpose to try to control weedy lakes,Ricciardisaid.

In recent years, the species has occasionallyended up in North American waters after being brought over alive to be sold in fish markets as a delicacy.

A threat to wetlands and smaller fish

Some varieties ofAsian carp, such as the silver andbighead,reproduce quickly and can eat up to 20 per cent of theirbody weight in plankton each day.

The grass carp, by comparison, is not as big of anenvironmental threat, but poses problems of its own.

Grass carp eataquaticvegetation, often uprooting large areas of vegetation, creatingproblems for smaller fish that use plantsto evade predators, Ricciardi said.

"It is a fish that feeds on plants and it feeds voraciously on plants," he said.

"If such a thing wereto become established [and begin reproducing]in the river or anywhere in the Great Lakes, it would be a threat if it was in a dense population to wetlands and all the things that depend on wetlands."

Chances it was the only one? Slim

MichelLegault,aQuebec government biologistheading the new project,said the province is consulting with experts in the United States and in Ontario, where grass carp have been discovered in Lake Erie.

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"We're still trying to determine where the fish came from," he said in an interview.

According to preliminary analysis, the specimenwas probably between 15 and 30 years old. Legaultsaidthe fish's belly was full of sterileeggs but was likely able to reproduce in the past.

At this point, he said it's too early to say whether there are more grass carp in the St. Lawrence River.

In Ricciardi's view,the chances of it being the only grass carp in the body of water is "unlikely."

"It certainly is a signal that the Quebec government was right to start a project," he said.