Bioenergetics modelling of grass carp: Estimated individual consumption and population impacts in Great Lakes wetlands

Grass carp (Ctenopharyngodon idella), native to eastern Asia, have established populations throughout the Mississippi River basin and are now reproducing naturally in the Great Lakes basin. As a large herbivorous fish, there is concern that an established grass carp population in the Great Lakes may threaten nearshore vegetated areas and wetlands. We parameterized a bioenergetics model for grass carp from the primary literature to quantify individual consumption levels and estimate the impacts of an established population on macrophytes in representative areas of Lakes Erie and Ontario. Individual life time consumption was estimated under average, cool and warm temperature conditions. Under average temperature conditions, a population of grass carp could consume up to 27.6kg of vegetation per kg of fish per year, depending on energy density of the vegetation. When consumption was estimated for populations of various grass carp biomass densities, most simulated scenarios resulted in <50% of vegetation remaining in an invaded wetland after one year, with the majority of consumption from pre-adult stages. Direct impacts will likely exceed these effects due to losses to vegetation production potential from grass carp feeding early in the growing season and grass carp foraging activity resulting in plant damage or uprooting.