Research Document 2016/101

Modelling Survival and Establishment of Grass Carp, Ctenopharyngodon idella, in the Great Lakes Basin

By Jones, L.A., Drake, D.A.R., Mandrak, N.E., Jerde, C.L., Wittmann, M.E., Lodge, D.M., van der Lee, A.S., Johnson, T.B., and Koops, M.A.

Abstract

Grass Carp (Ctenopharyngodon idella), is a large, herbivorous fish that was first introduced to North America in 1963 for aquatic macrophyte control. It has since escaped from where it was stocked and entered rivers of the central United States and has dispersed through the Mississippi River basin towards the Great Lakes. Commerce is also another source of spread in the United States, where sale of diploid and certified triploid (reproductively sterile) Grass Carp is legal in several states. Between 2007 and 2012, 45 Grass Carp were known to have been caught in the Great Lakes basin, raising concerns that a sufficient number of individuals are present and may be able to form a self-sustaining population. The potential for Grass Carp to invade the Great Lakes is of increasing concern and there is a management need to understand the probability of introduction and the potential ecological consequences of Grass Carp to the Great Lakes basin. Three modelling approaches were used to inform the likelihood of Grass Carp survival and establishment in the Great Lakes basin.

First, a bioenergetics model is presented to assess the likelihood of Grass Carp survival. Model results predicted growth and survival in the Great Lakes is possible using a variety of diets including solely Cladophora spp. A reproductive-sized Grass Carp weighing approximately 3 kg required approximately 15 kg of macrophytes annually to maintain body weight. This is likely achievable based on mean macrophyte biomass estimated in different regions of the Great Lakes. The potential loss of macrophytes from individual consumption pressure could be amplified if feeding preference or foraging behaviour result in plant damage beyond what is consumed (e.g., shifting macrophyte composition). The second modelling approach used the net reproductive value to assess the potential for establishment in the Great Lakes basin. The net reproductive rate (R₀) for Grass Carp in the Great Lakes was 24.8, indicating that Grass Carp are likely to establish in the Great Lakes. Varying the model to include slower maturation times for reproduction yields the same result of successful establishment. Third, a stochastic model was used to predict the overwinter survival of young-of-year (YOY) Grass Carp to estimate the likelihood of establishment. Overwinter mortality of YOY ranged from 0.42 to 1.0, with 100% mortality in more northern locations within the Great Lakes. These modelling approaches predict that Grass Carp has the potential to survive and establish in the Great Lakes basin.

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