Stopping the spread of the invasive grass carp

Photo by Dan Koehler

The Lake Ontario shore in Oshawa, where grass carp could be in less than 10 years unless action is taken.

One of the four species of invasive Asian carps, the grass carp, has arrived in the Great Lakes, says a report from Fisheries and Oceans Canada (DFO) released on Jan. 27.

The species, which shares similarities with bighead and silver carp but differs in diet, presents a serious risk to native fish and their habitats.  Unlike silver carp, they don’t pose a risk to people and can reach a size of two to three feet.  Grass carp have been found in both Lake Michigan and Lake Erie, and are likely to reach Lake Ontario within five years unless something is done.

“If there are no additional actions taken there is a risk that grass carp could become established in the great lakes,” said Becky Cudmore, aquatic invasive species senior advisor for DFO and manager of its Asian carp program in a phone interview.

Grass carp feed solely on aquatic vegetation which is important for native fish like large-mouth bass and walleye.

“Its feeding patterns are particularly harmful to wetlands, embayments, and near shore areas,” said Marc Gaden, communications director and legislative liaison for the Great Lakes Fishery Commission in an interview.

Without proper wetland habitats, young fish are left unprotected and can succumb to predators.

“Those are really valuable areas for a lot of our fish to use as nurseries for their young,’” said Cudmore.

Although grass carp have yet to establish in the Great Lakes, their presence is enough to bring forth action, Gaden said.

“Because the fish that have arrived are fertile, the likelihood of establishment is very high within 10 years,” said Gaden.

Grass carp were first introduced into the United States to control aquatic vegetation in the 1960s.  According to the report, grass carp likely made it to Lake Michigan through the Chicago-Area Waterway System (CAWS).

The CAWS has since been secured to prevent specimens moving into the Great Lakes but not before the grass carp made their way north.

The report was a combined effort between the United States and Canada, said Cudmore.  The effort is focused on not letting a population of these fish establish, she said.

“We’re not thinking about international borders because the fish aren’t,” said Cudmore.

According to Brook Schryer of the Ontario Federation of Anglers and Hunters (OFAH), grass carp can lay more than one million eggs and reach 25 centimetres within one year.  Education and outreach are essential to preventing their establishment, he said.

One way this is being done is through the OFAH Invading Species Awareness program, a joint initiative between the OFAH and MNRF started in 1992.

The program attends trade shows and promotes invasive species awareness through social media.  They even have a mascot, Captain Carp, to help reach out to all ages.

“This past summer he traveled all around southern Ontario to various events,” said Schryer in a phone interview.

Schryer said since grass carp eat only vegetation, they can rarely be caught by recreational anglers.

“It’s not like grass carp are going to replace the angling opportunities that our native fish species provide,” said Schryer.  “You can’t efficiently angle for these guys.”

Both Schryer and Cudmore said if you come across a grass carp the best thing you can do is report it.  This can be done by calling the toll-free Invading Species Hotline at 1-800-563-7711, emailing, or submitting a report through

“The more eyes on the water the better,” said Cudmore.


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Dan is a second-year journalism student at Durham College, who enjoys writing about music, the environment, politics, and opinion pieces. He also hosts a show on Riot Radio and works as a volunteer technician. Dan loves spending time at his cottage and has a wide array of unusual pets, including reptiles and arachnids. In the future he hopes to work for a radio station while doing freelance photography.