Back to the Fishway What is a carp? Carp introduction Carp ecology Carp elimination Exotic fish What is a carp? Carp, native to temperate regions of Asia, are one of the many non-native invasive species found within our nature sanctuaries. Closely related to the goldfish, and the largest member of the minnow family, the common carp (Cyprinus carpio) is identified by its long dorsal fin, olive-green back, yellowish sides and sucker mouth.  Carp are a fast growing fish, maturing at two to four years of age (35 to 45 cm, ~1 kg), and may live up to 40 years, reaching 110 cm (40kg). The average carp caught at the Fishway weighs between two and 11 kilograms, but carp as large as 25 kilograms have been caught there. The foraging and spawning behaviour of carp is one of the key human-induced marsh stressors contributing to the degradation of the Gardens’ marsh habitats. Carp exclusion has been seen as the necessary first step in marsh habitat restoration by the Gardens since the 1940s. Since then, many attempts have been made to eliminate carp from the marsh including commercial fishing and net barriers in the early 1950s, to the present and very successful operation of the Fishway and Christmas tree exclosures.  Carp elimination benefits all levels of the marsh environment as it allows for the re-growth of aquatic plants—the foundation of a healthy marsh ecosystem. Back to Top History of carp introduction Carp are valued as a food source in many cultures, and human activity has taken this fish species across the globe. For centuries carp were used to stock fish hatcheries. They have an adaptable diet, grow to a large size very quickly, and thrive in warm, nutrient rich waters. First introduced to New York State in 1831—after decades of intentional and accidental releases—they are now abundant throughout the Great Lakes and much of southern North America. Carp were first introduced to Lake Ontario in the 1870s when they were raised and stocked at a Wilmont Creek fish hatchery as a replacement for the disappearing Atlantic salmon.  By the 1930s, carp had become the dominant species throughout the Gardens’ 300 hectares of marshlands. In the early 1990s, before the installation of the Fishway, carp were found at extremely high densities (800 kg/ha). Serious ecological impacts begin occurring once carp densities exceed 50kg/ha. The large carp population size is a result of a combination of factors including altered water quality, an altered lake water cycle and the fact that warm rivermouth marshes such as those found here are the preferred habitat of carp. Back to Top Carp ecology—wetland destroyers Due to their large size, both the feeding and spawning actions of carp can uproot and crush aquatic plants. Plants are the foundation of the marsh ecosystem, the loss of which can result in ecosystem collapse. Carp are specifically adapted to bottom foraging in the soft sediments of a rivermouth marsh environment. When feeding, carp force their face into the soft sediments using their sucker-mouth to inhale the bottom material. The inhaled sediment is then filtered through their gills, keeping the food (worms, aquatic insects, mollusks, crustaceans, decaying organic matter and seeds), while the fine sediment is sent back into the water. This behaviour physically uproots existing aquatic plants and re-suspends the bottom sediments, degrading the water quality and further impacting plant growth. Although this is a common feeding behaviour of a number of native Ontario fish (i.e. fathead minnow), no native fish nearly as large as carp uses this foraging style in the marsh. Carp depend on aquatic plants for spawning. Each spring when water temperatures approach 17degrees Celsius, groups of adult carp begin to congregate in the flooded vegetation to spawn. During spawning, a single female will be pursued by up to 20 males thrashing about and scattering their adhesive eggs onto the plants. This activity crushes both native plants and small aquatic organisms. A single 10-kg female carp carries approximately 1,000,000 eggs, making them an ideal species for quickly colonizing unstable marsh habitats. Back to Top Carp elimination The elimination of carp is an important step in the rehabilitation of the Gardens’ marshlands. Knowledge of their behaviour is a key factor in this process. Carp behaviour patterns include a spring migration into shallow marshlands, and fall migration out to the adjoining deeper waters of Hamilton Harbour. This movement is due to the fact that while carp prefer to spend the spring and summer in the marshlands, they must leave the marsh in order to survive the winter. Declining fall Lake Ontario and wetland water levels, and the formation of winter ice often leaves Cootes Paradise too shallow (less than 30 cm deep) for carp to survive. The fact that carp must leave the marsh to over-winter in the Harbour is what makes carp exclusion possible. Carp must migrate through the Desjardins Canal, the only channel that connects Cootes Paradise and Hamilton Harbour, allowing them to be intercepted and sorted at the Fishway each spring and fall. By excluding carp from the marshlands, they are prevented from accessing their main spawning area. And although the excluded carp may still spawn in other areas of Hamilton Harbour, the survival rate of their young is very low because they can’t access the appropriate nursery conditions that exist only in the shallow marsh environment. For this reason it is only necessary for the Fishway to exclude mature carp (> 35 cm long).  By not allowing adult carp into the marsh to spawn, over time, the overall carp population in the area will decline. Back to Top Science contacts Ask our science staff a question about the science and conservation program. Science fact sheets Download a fact sheet and learn about our restoration projects. Directions Click here to see how easy we are to find. Local weather Find out the local forecast before you head out!
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