Grass Carp: The New Threat to The Great Lake’s Fishing Industry
If fishing the Great Lakes is your passion, keep reading to learn how a Grass Carp invasion could affect your future angling experience!
A Quick Refresher: What Are Grass Carp?
Grass Carp are invasive freshwater fish that belong to the Cyprinidae family, meaning they are closely related and share characteristics with multiple species of carps and minnows. Grass Carp are native to the rivers, reservoirs and lakes of China and southern Russia but have been forming established invasive populations throughout the Southern United States over the last 40 years. Grass Carp are primarily herbivorous fish species, capable of consuming up to 40% of their body mass each day in aquatic vegetation. This aggressive eating behaviour grabbed the attention of aqua culturists. In the early 1970s, Grass Carp were introduced into the Southern United States and utilized for vegetation/algae control in aquaculture facilities and ponds. Flooding events allowed this invasive species to escape these facilities and move beyond contained environments into natural open freshwater systems, such as the Mississippi River Basin, where they have since become heavily established and begun to spread. Grass Carp pose significant ecological threats to the Great Lakes through aggressive feeding and removal of aquatic vegetation, resulting in habitat loss and degradation affecting a wide variety of native fish species. Although it is true that there are currently no established populations of Grass Carp in the Canadian waters of the Great Lakes or anywhere in Canada, risk assessments suggest if no additional actions take place soon, the overall ecological risk of Grass Carp to the Great Lakes is high, especially to the central lakes, with impacts of Grass Carp increasing over time.
Grass Carp have oblong shaped bodies, a flattened head, and moderately small eyes centred on the side of the head. Their scales are large and overlapping, with coloration ranging from blackish to olive-brown with brassy or silvery-white on the sides and belly and outlined by darker-coloured pigments on the back and sides. This gives them a cross-hatched/ checkered appearance. It can take up to 2 years for Grass Carp to reach sexual maturity, but sometimes over a decade to grow to their maximum size. Grass Carp can grow quite large, reaching weights surpassing 80 pounds and lengths of 1.5 metres!
Photograph by: Toronto and Region Conservation Authority
How Would Anglers Be Affected?
As a primarily herbivorous fish that typically does not consume or attack other fish species, it may come as a surprise how much damage and impact introduced Grass Carp can have on native fish populations. There are numerous ways that Canadian anglers could be impacted by a Grass Carp invasion, but the most prominent impacts could include reductions in freshwater sportfish populations and decreases in water quality.
Grass Carp can negatively modify habitats, compete with native fishes for food and resources, and act as carriers for diseases or parasites that could spread to native fishes. The eating habits of Grass Carp can disturb lake and river bottoms, leave native small/ juvenile fishes without sufficient protection from predators, and reduce possible spawning habitats for species that prefer to nest in aquatic vegetation. Grass Carp can grow to reach considerable sizes and develop appetites just as large. Capable of reaching weights of 80+ pounds and lengths surpassing 5 feet, it takes a lot of food resources to keep them fed. Grass Carp eat primarily aquatic plants, with a single individual capable of consuming up to 40% of its body weight in aquatic vegetation daily. This could potentially range from 20 to 30 pounds a day for a fully-grown Grass Carp! In addition, these invasive carp grow very large very quickly, and it is unlikely that their populations would be controlled by native predators in the Great Lakes basin if they were to establish, as they would outgrow the gape (mouth) size of native predatory species. Aquatic vegetation plays an important role in aquatic ecosystems such as providing shelter for native species, food, refuge from predators, nesting habitat for countless species, producing oxygen, regulating water quality and more.
At Risk Sport Fish Species
High impacts are predicted for over 30 native freshwater fish species in Canadian waters upon Grass Carp establishment due to habitat loss and resource competition. Examples of species that are predicted to experience impacts include but are not limited to the following:
Spotted Gar
Longnose Gar
Bowfin
Grass Pickerel
Northern Pike
Muskellunge
Green Sunfish
Pumpkinseed
Warmouth
Bluegill
Largemouth Bass
Smallmouth Bass
White Crappie
Black Crappie
Yellow Perch
White Bass
Impacts to Canada’s Fishing Industry
The Great Lakes contribute $13.8 billion to the Canadian economy every year through commercial, recreational and subsistence fishing, water use, water-based hunting, oil and gas, commercial navigation, recreational boating, beach / lakefront use, and wildlife viewing. Among this value, recreational fishing is an extremely valuable venture responsible for contributing roughly $556 million CAD to Canada's economy annually. Grass Carp could damage this economic value by reducing the population sizes of favoured angling species. A Grass Carp invasion would mean limited food availability and increased stress on native aquatic wildlife, which could decrease total lengths and weights in native sport fish species.
A large amount of money is contributed to Canada's economy via anglers through the purchase of fishing licenses, fishing equipment, gear, and tourism. Reduced recreational fishing due to decreased water quality and diminished sport fish availability would affect other small businesses and livelihoods that depend on the growth of this sector, including bait and tackle shops. The rapid loss of native species could also put more pressure on stocking efforts by government-funded hatcheries, which may be forced to stock more frequently to keep up with the rapid loss of natural populations, and possibly experience a reduction in funding.
How Anglers Can Make a Difference
Grass Carp are currently not established in Canadian waters, and we all have a role to play to make sure it stays that way! Those such as anglers and watercraft users who spend the most time out on the water act as the first line of defence against Grass Carp introductions and play a very crucial role in prevention. Here are some simple ways anglers can lend a hand:
Never release the contents of a bait bucket back into any waterbody. In Ontario, it is illegal to deposit or release baitfish into or within 30 metres of any waters (including onto the ice), as they may contain invasive species or their eggs! Click here to view the Confused with Carp: Baitfish Guide
Learn how to identify invasive Grass Carp and how to differentiate them from native look-a-like species. Click here to view the Grass Carp Identification and Reporting Guide. Click here to view the Confused with Carp: Common Look-a-Likes Guide.
If you think you have seen or captured a Grass Carp, take a photo, and report it to the Invading Species Hotline at 1-800-563-7711 or EDDMapS.org DO NOT release it!
If you can't reach anyone, kill the fish without damaging the head or eyes and keep the fish in a cooler with the head above ice ensuring the eyes do not freeze, as The Department of Fisheries and Oceans will collect the fish and the eyes are important for further analysis.