MANAGEMENT OF AQUATIC PLANTS IN MULTI-USE LAKES WITH GRASS CARP (CTENOPHARYNGODONIDELLA)

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Abstract
Recent hatchery advances producing sterile triploid grass carp and the relaxing of state and federal restrictions on their distribution are expected to result in widespread use of these fish for aquatic plant management in North America. This large Asian cyprinid is a voracious herbivore and must be used properly to avoid major reductions in desirable aquatic vegetation. Grass carp exhibit strong food preferences and should only be used to manage plants that they prefer. Their use to manage plants that they do not prefer can result in expansion of the target plant and severe reductions in non-target species. Food preferences must be verified regionally. For best results, plant biomass should first be reduced and then grass carp should be stocked at 2 fish per metric ton of remaining vegetation. Grass carp should not be used to control aquatic plants in waterfowl management areas. Because grass carp are very difficult to recapture, overstocking should be avoided. Overstocking grass carp has resulted in near complete elimination of submersed plants and severe reductions in many emersed species for periods greater than 10 years. Use of grass carp can increase turbidity, phytoplankton, and nutrient concentrations in the water column but to a lesser degree than can occur using most aquatic herbicides. Provided that they are not overstocked, triploid grass carp appear compatible for use in fisheries management areas.