Studies Of Gizzard Shad Reduction At Lake Beulah, Florida

Four experiments with 0.1 p.p.m. or less of 5 percent emulsified rotenone were conducted at Lake Beulah, Florida. Lake Beulah, an eighteen-acre lake with an average depth of 14.9 feet characteristically had a heavy plankton production. Estimated pounds of gizzard shad killed progressively declined during the four experiments although concentrations of rotenone were increased. The first kill was estimated at 23,455 pounds of shad; second kill, 7,976 pounds; third kill, 1,528 pounds; and fourth kill, 1,060 pounds. Small numbers of fish of other species were also killed. Length-frequency studies of gizzard shad indicated an over populated condition existed at the time of the first poisoning. Thereafter reproduction and rapid growth of this species occurred. Evidence exists that threadfin shad may have been eliminated from Lake Beulah following the use of the selective poisoning technique. Total kill calculations included results from bottom sample screens. An inverse relationship existed between average temperature and the percent of all fish killed which did not float to the surface.

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