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.

Invasive species that 'feeds voraciously on plants' prompts roll out of $1.7M government detection plan

Tommy Goszewski, a technician with the U.S. Geological Survey, holds a grass carp taken from a pond at an agency lab in Columbia, Mo., in 2013. Two fishermen recently reeled in a grass carp in the St. Lawrence River. (AP Photo/U.S. Geological Survey)

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, two fishermen in Quebec's Lanaudière region reeled in the 29-kilogram specimen.

The fish is native to east Asia, but has been used in North America as a way to manage aquatic vegetation and is viewed by some as a culinary delicacy.

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

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

This grass carp caught on May 27 is the first one discovered in the St. Lawrence River. (Dominic Brassard/Radio-Canada)
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," Anthony Ricciardi, an invasive species biologist at McGill University, told CBC Montreal's Homerun.

Grass carp have been in North America since the 1960s and were brought in to the United States on purpose to try to control weedy lakes, Ricciardi said.

In recent years, the species has occasionally ended 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 of Asian carp, such as the silver and bighead, reproduce quickly and can eat up to 20 per cent of their body weight in plankton each day. 

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

Fishermen captured this grass carp on May 27 in the St. Lawrence River near Lanoraie, Que. (Dominic Brassard/Radio-Canada)

Grass carp eat aquatic vegetation, often uprooting large areas of vegetation, creating problems for smaller fish that use plants to evade predators, Ricciardi said.

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

"If such a thing were to 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

Michel Legault, a Quebec government biologist heading 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.

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

According to preliminary analysis, the specimen was probably between 15 and 30 years old. Legault said the fish's belly was full of sterile eggs 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.

With files from The Associated Press