Improving Undesirable Fish Populations

Improving Undesirable Fish Populations

Undesirable fish populations can develop if bass numbers are low, if bass were never stocked, or if the pond has turbidity or vegetation problems. If anglers catch mainly 3- to 6-inch bluegills and few or no bass are taken, it is likely that either (1) bass overharvest has occurred, (2) bass are not present, (3) bass cannot see to feed, or (4) excessive aquatic vegetation has made bluegill unavailable to bass. The first two problems can be rectified by stocking 50 8- to 12-inch bass per acre. If the pond has an underwater visibility of less than 12 inches or if over 50% of the surface area of the pond is covered by vegetation, these problems must be treated before bass are stocked. Procedures for dealing with “problem ponds” are discussed in the next section. If turbidity problems cannot be overcome, the pond owner might consider stocking 100 8-inch and longer channel catfish per acre and forget about trying to produce bass and bluegills. After 8-inch bass have been stocked in a clear pond, bass less than 15 inches long should not be harvested for a 3-year period (2 years if 12-inch bass were stocked). Then, one of the four management options previously described should be followed, depending upon pond owner and angler desires.

If only small bass and no bluegills are caught, 100-250 4- to 5-inch or larger bluegills should be stocked per acre. Then, appropriate bass harvest restrictions and stocking strategies should be followed as outlined in one of the four management options.

If the pond contains neither bass or bluegills and small bullheads and green sunfish are present, 50 8- to 12-inch bass should be stocked per acre. Once the bullheads or green sunfish are under control, 100-250 4- to 5-inch or larger bluegills should be stocked per acre because bullheads and green sunfish will not provide adequate prey to sustain a desirable bass population.

In the absence of bass, bullheads and carp sometimes develop such dense populations that their bottom feeding activities roil the water severely. Even if bass were stocked in such ponds, they could not see to feed, and their impact on bull heads and carp would be negligible. Draining the pond is the most economical alternative for removing unwanted fish given these circumstances. If the pond cannot be drained, the fish community can be chemically removed. Liquid rotenone (5% or 2 1/2% synergized) is the chemical most frequently used. The chemical kills only animals with gills and is not harmful to warm-blooded animals. It should be mixed at a volume of 1 gallon per acre-foot of water. The amount of rotenone required may be reduced if the pond’s water volume can be lowered through siphoning or pumping. This is desirable because the chemical is expensive. Application of rotenone must be conducted by a registered herbicide applicator and a permit is required from the Kansas Department of Health and Environment. Contact a district fisheries biologist for further information.

Treatment should occur when the water temperature is 70°F or above. In ponds smaller than about 2 acres, the chemical should be mixed into the water using the propwash of a stationary outboard motor. The front end of a small boat should be pointed into the pond’s bank and the motor should be run in forward gear while the rotenone is poured slowly into the propwash. It is best to dilute the rotenone with water before it is poured into the pond so that the treatment is done gradually. The propwash will circulate the chemical to all depths of the pond. The motor should be run as fast as safely possible to assure maximum circulation. The front and sides of the boat should be tied to stakes driven into the pond’s bottom to keep the boat from running up the bank.

It is important to change the location of the boat several times so that the mixing action reaches all areas of the pond. Shallow areas or areas not reached by the propwash should be treated with a hand sprayer or by “bucketing” in the chemical. The mixing action is ineffective when the boat is only driven around the pond. While the upper 3 feet of water may be well mixed, little chemical will reach lower depths.

Rotenone may not reach all areas of large ponds or ponds deeper than 10 feet when the chemical is mixed with an outboard motor. The chemical should be pumped into areas not reached by motor mixing and into the deepest portions of such ponds. Fish can be stocked back into a pond within 3 weeks after rotenone has been applied.