Agenda - 05-02-1994 - V-C - Laserfiche WebLink

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1 2 misguided attempt to provide habitat for game fish. Aquatic week specialists generally attribute approximately ninety percent of the spread of hydrilla infestation to human activities. The first official identification of hydrilla in Lake Orange occurred in October 1992, although there is anecdotal evidence that hydrilla may have been present for ten or more years prior to that. Immediately upon their identification of hydrilla in Lake Orange, Cooperative Extension officials notified the NC Division of Water Resources (DWR) . DWR is the state agency which has responsibility for responding to hydrilla problems. Dr. David DeMont, director of the Aquatic Weed section of DWR, made a site visit to Lake Orange shortly thereafter to confirm the presence of hydrilla and to assess the severity of the infestation. By January 1993, DWR staff had completed a field survey and measurement of the hydrilla infested areas of Lake Orange. The survey indicated that approximately eighty acres (fifty percent of the normal surface area) of Lake Orange were infested with hydrilla. A North Carolina Cooperative Extension Service publication which describes the state's hydrilla problem outlines a number of methods which have been used to control hydrilla. The literature indicates that many of the traditional methods of acquatic weed control, including those which involve draining a lake and mechanically removing the weed growth, are expensive and ineffective in eliminating hydrilla. Two methods of treatment which have been successful in suppressing hydrilla are: a) periodic application of specialized aquatic herbicides; and b) stocking an infested lake with genetically sterilized (non-reproducing) grass eating carp. The herbicides are commonly used in lakes which provide water for human and livestock consumption and are considered to be non-toxic to wildlife. The primary disadvantage to aquatic herbicides is expense. Significant quantities of the herbicide must be used in each of several applications per season. The use of herbicides to provide treatment of all infested areas of Lake Orange would cost tens of thousands of dollars per year. The method of controlling hydrilla with grass carp is very economical. The carp, which seem to prefer hydrilla to other desirable acquatic weeds, consume up to three times their weight in hydrilla each day and are stocked at a rate of twenty fish per acre of infestation. The carp are approximately ten inches long and weigh less than one pound introduced into a lake. Grass carp may live up to ten years and, at maturity, can exceed thirty-six inches in length and weigh in excess of twenty pounds. Dr. DeMont has determined that the extent of the hydrilla infestation at Lake Orange requires that the lake be stocked with 1800 grass carp at total cost of approximately $8000.