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Research Document 2016/118

Ecological Risk Assessment of Grass Carp (Ctenopharyngodon idella) for the Great Lakes Basin

By Cudmore, B., Jones, L.A., Mandrak, N.E., Dettmers, J.M., Chapman, D.C., Kolar, C.S, and Conover, G.


A binational ecological risk assessment was conducted to determine the extent of the risk of Grass Carp (Ctenopharyngodon idella) to the Great Lakes basin and to provide useful, scientifically defensible advice on prevention, monitoring, early detection, and potential management actions for managers and decision-makers in Canada and the United States. This risk assessment covered both triploid and diploid Grass Carp. It assessed the probability of occurrence (likelihood of arrival, survival, and spread) for triploid Grass Carp, and the probability of introduction (likelihood of arrival, survival, establishment and spread) for diploid Grass, as well as the potential magnitude of ecological consequences within 5, 10, 20, and 50 years from 2014 (i.e., the baseline year). Arrival routes assessed were physical connections, human-mediated release (bait use, trade and stocking) and laker ballast. The most likely pathway of arrival for triploid and diploid Grass Carp into the Great Lakes basin was considered to be through the category of physical connections, specifically the Chicago-Area Waterway System into Lake Michigan. However, it is important to note that Grass Carp (both triploid and diploid) has already arrived to lakes Michigan and Erie. Based on thermal tolerance, food availability, predation, and pathogens and diseases, juvenile and adult Grass Carp will survive in the Great Lakes. Results of this risk assessment show that conditions exist to support establishment (e.g., suitable spawning and nursery habitat, potential for positive population growth, overwinter survival of early life stages) of diploid Grass Carp, and that establishment is very likely to occur within 10 years for lakes Erie, Michigan, Huron, and Ontario. However, establishment at northern latitudes of Lake Superior is less certain based on limited overwinter survival of young-of-year and ability to reach maturity. While no impediments to spread exist among the lakes, spread is of greatest concern to the other Great Lakes in the basin based on the arrival of Grass Carp in lakes Michigan and Erie; with movement from Lake Michigan to Lake Huron and from Lake Erie to Lake Ontario expected within 10 years. Should diploid Grass Carp become established, submerged aquatic vegetation will decrease or change in species assemblage, which may lead to consequences to other elements of the biotic community (e.g., birds, fishes) and abiotic environment (e.g., turbidity, nutrient cycling). These effects may be greater within localized wetlands if Grass Carp aggregate in these areas. Overall risk for triploid Grass Carp ranges from low to medium for all years and lakes. For diploid Grass Carp, overall risk is highest for lakes Michigan, Huron and Erie, followed by Lake Ontario and Lake Superior.

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