August 6, 2019


Invasive Species are covered under the Great Lakes Water Quality Agreement and the most threatening species to Georgian Bay wetlands is Grass Carp. Most of the talk about invasive Asian carps is about the carp species south of Chicago. Grass carp are different and have been found in Lake Erie and Lake Huron and are now reproducing in 2 Ohio rivers. They spawn 2 to 3 times a year and each female can lay up to 500,000 eggs at each spawn.

The time for research is over. The 2017 binational Grass Carp Risk Assessment determined that it would take 10 years for them to invade Lake Huron but stated that “If the rate of arrival increases, the onset and magnitude of risk will increase.” Shockingly, they were caught in 2018 in Lake Huron – just one year later!

Grass carp grow very rapidly. Young fish 20 cm (7.9 in) can grow to over 45 cm (18 in) by fall. Their maximum length is 1.4 m (4.6 ft) with a maximum weight of 40 kg (88 lbs). They eat up to three times their body weight each day. The principal issue with Grass Carp is their ability to colonize habitat that is occupied by native species. Their sheer numbers simply out-compete native species for space and food and destroy habitat that is occupied by young native fish species. This would include destruction of spawning habitat for species such as yellow perch, northern pike and muskellunge, largemouth bass, sunfish and rock bass. Grass Carp, with their voracious appetites, also pose a serious threat to the very existence of wetlands. Wetlands, according to the Great Lakes Wetlands Consortium, provide $1500/acre annually in ecological services including filtering out contaminants and nutrients.

In spite of the imminent risk these fish pose to the Great Lakes, the Ohio and Michigan Departments of Natural Resources together with Michigan State University have been conducting research that includes catching, tagging and live releasing these invasive fish. Canada’s Department of Fisheries and Oceans for 2 years has been calling for Ohio to begin an eradication program. The IJC can play an important part in this needed eradication by strongly recommending to the US State department that eradication action by Ohio and Michigan begin this summer and their “research” program be terminated.

Grass Carp Held By US Fish and Wildlife Staff