At least two living specimens of Asian carp have been identified in the Richelieu River, a situation that concerns the Quebec Ministry of the Environment, since these fish represent a threat to the ecosystems of the waterways where they settle. The United States has been stuck with this family of invasive species for several years.
The two grass carp were observed at the Vianney-Legendre fishway, which is located at the Saint-Ours dam on the Richelieu River. The Ministry of the Environment, the Fight against Climate Change, Wildlife and Parks (MELCCFP) hopes to capture grass carp “to analyze them and try to confirm their provenance”.
“Given their rapid growth, voracious appetite and diet consisting of aquatic vegetation, grass carp can severely damage fish habitat, disrupt the functioning of aquatic ecosystems and affect water quality,” explains the MELCCFP in the press release issued announcing the observations.
“Even without forming a viable long-term population, grass carp can cause significant damage to aquatic grass beds on which many native fish species depend for food or reproduction,” the ministry adds. In the case of the Richelieu River, the situation is all the more worrying because the copper redhorse, an “endangered” endemic species, lives there.
Fish and DNA
The two fish observed in the Richelieu River were the third and fourth grass carp recorded alive in Quebec since 2016. That year, a fisherman caught a 27-kilo individual in Contrecoeur. A second grass carp was caught in July 2020 by a sports fisherman in the Chambly basin. This species can exceed one meter in length and weigh more than 50 kilos in adulthood.
In addition, several positive detections of grass carp environmental DNA have been documented each year since 2017 in the Richelieu River by the MELCCFP. Positive samples were thus collected at the mouth of the Rivière des Prairies, just east of the island of Montreal, in the Lake Saint-Pierre archipelago and in the lake itself, near the mouth of the Saint-François river.
Asian carp were imported into the United States in the 1970s for aquaculture purposes. Thanks to floods, they were able to reach the Mississippi River, then go up the mythical river and invade the waterways attached to it over a distance of more than 1,500 kilometers.
Grass carp, one of the four species of Asian carp, is already present in the Great Lakes, which are connected to the St. Lawrence River. Furthermore, breeding of the species has been confirmed in two rivers flowing into Lake Erie.
According to Fisheries and Oceans Canada, if the species takes hold in the Great Lakes, this Asian carp “could become the dominant species to the detriment of native species”, “virtually eliminate aquatic plants” and even be “harmful” to the habitat of bird species.