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Grass Carp in Lake Gaston

By:   Boyd Strain and John Slaton
        Lake Gaston Weed Control Council

Date: June, 2004

Grass carp (Ctenopharyngodon idellus) is a large plant eating fish with a feeding  preference for Hydrilla. At approximately 20 fish per vegetated acre, they have been shown to eliminate Hydrilla.  When stocked in lakes and ponds, however, grass carp will eat veraciously and have been known to eliminate all green plants. In 1995, approximately 6.5 grass carp per infested acre were stocked into Lake Gaston by the Lake Gaston Weed Control Council.  5,000 were added in 1999.  No restocking was done until 2003.  We were permitted to add 8 per infested acre in 2003 for a total of 25,392 grass carp.  We are requesting the maximum allowed for loss to attrition of 40% or 10,157 this year.

The Wildlife departments of North Carolina and Virginia have statutory authority to issue permits for stocking of grass carp into public waters. To help control Hydrilla but protect Lake Gaston from excessive plant removal, the departments have agreed to allow the stocking of grass carp of up to 8 carp per acre of weed infestation in 2003 and to review each year an amount based on attrition or 3 to 5 per acre. This will be determined after a Fall survey.   

Fisheries experts agree that it is necessary to maintain desirable plants in the water to provide food and habitat for fish and other wildlife. If too many grass carp were inserted it would be very costly to remove them and to re-vegetate the lake with desirable aquatic plants. Consequently, the current weed management plan is to conduct an intensive weed removal campaign using appropriate chemical herbicides on targeted noxious weeds. In addition, with yearly reviews, grass carp are to be maintained at approximately 8 fish per infested acre with the assumption that this number can maintain Hydrilla at low levels without damaging native plants.