Research Document 2016/114
Modelling spread and assessing movement of Grass Carp, Ctenopharyngodon idella, in the Great Lakes basin
By Currie, W.J.S.,Kim, J., Koops, M.A., Mandrak, N.E., O’Connor, L.M., Pratt, T.C., Timusk, E., and Choy, M.
Grass Carp (Ctenopharyngodon idella), a species of Asian carp, was first introduced to North America in 1963 for aquatic macrophyte control. It has since escaped from impoundments where it was stocked and entered rivers of the central United States and has continued making its way up the Mississippi River basin towards the Great Lakes. Diploid (i.e., fertile) and triploid (i.e., functionally sterile) Grass Carp continue to be used for various purposes (e.g., biological control, polyculture) with varied regulations across states and provinces. Currently, Grass Carp is in close proximity to the Great Lakes basin with increasing occurrences in the Great Lakes basin itself including within the Grand River, Ontario, and there is recent evidence of recruitment within the U.S. waters of western Lake Erie. Management agencies need to understand the risk that Grass Carp poses to the Great Lakes. Ecological risk assessment evaluates the probability of introduction (i.e., arrival, survival, establishment and spread) and the potential ecological consequences of a species (Mandrak et al. 2012). Predicting and assessing the potential spread within and between lakes by natural dispersal is a critical step in understanding and preventing the spread of Grass Carp if it was to arrive and establish in the Great Lakes basin. Most existing research on Grass Carp movement has been undertaken in aquaculture ponds and river systems, which are quite different from large lakes. As such, a modelling approach, using information available up to 2014, was applied to address the likelihood of Grass Carp spread within the Great Lakes basin. An area-restricted individual-based model was used to predict spread rates and regions likely to attract Grass Carp when released from two of the most likely invasion sites: Chicago Area Waterway System, Lake Michigan; and, Maumee River, Lake Erie. Model results indicate that at slow and fast movement rates, Grass Carp is expected to reach another basin from the one in which it was introduced within 5–10 years. Further assessment of the likelihood of spread of Grass Carp within the Great Lakes basin was accomplished by examining the potential pathways (i.e., lock and canal systems) that Grass Carp may use to spread between the Great Lakes. Two in situ experiments assessed the likelihood of spread by direct natural dispersal through canals and locks between lakes Erie and Ontario, and between lakes Huron and Superior. Tagged fishes moved between lakes Erie and Ontario (7 out of 179) and between lakes Superior and Huron (8 out of 152) by moving through the locks and canals between these lakes; however, few tagged individuals managed movement of this extent. Together, these results demonstrate that Grass Carp is likely to spread into all of the Great Lakes if it arrives and establishes, but spread to Lake Superior, if it occurs, will likely take much longer.
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