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352 CHAPTER 14 fyke nets) are effective only in shallow waters since fish often swim over the leads in deeper water. Seines and trawls may have some promise for control in special situations but those gears require a relatively smooth bottom, free of snags (a condition rare in most waters), to be fished properly. In small farm ponds with smooth bottoms, seines can be used effectively. Wing nets and trap nets are effective for crappies, bullhcads, sunfish, and gizzard shad in shallow waters. Passive gear such as gill ncts and trammel nets are effective on various species of fish when the fish are active. Weirs can be effective in streams when fish are migrating, but require cleaning of waterborne debris from the mesh. The main drawback in using nets is that they require a great deal of human effort, and are rather expensive equipment that must be repaired or replaced fairly often. Nets may also cause some mortality of desirable game fish. Commercial fishers use nets designed to catch certain sizes of fish, but are seldom designed for control of a given species. Usually catches will be largest at the beginning of the netting operation. As the fish population declines, the catch per unit effort will drop making netting inefficient. 14.7 CONCLUSION If a fish species is considered undesirable, a variety of management methods (e.g., chemical, biological, or mechanical) should be considered to achieve carefully planned and predetermined objectives. The goals and objectives that are determined for control of undesirable species must be realistic in terms of success that may be achieved and costs related to benefits. Complete control of undesir- able fish is seldom possible and partial controls must remove enough of the undesirable fish population so that competition or predation on desired fish are reduced. Control programs should be carefully evaluated to determine if reason- able predictability of the outcome of the control method is possible. Fisheries managers must be flexible to increase or decrease management efforts depending on the response of the target fish population. Control, using the most effective methodes), should be applied at a time and location when the pest species is most vulnerable. At the same time, control should be implemented when there is the least risk of adverse impacts (Berryman 1972). Often the concept of integrated management (using a combination of methods) may be necessary to achieve selective manipulation of fish populations. 14.8 REFERENCES Albertson, L. M., B. R. Smith, and H. H. Moore. 1965. Experimental control of sea lampreys with electricity on the south shore of Lake Superior, 1953-60. Great Lakes Fishery Commission Technical Report 10. Berryman, J. H. 1972. The principles of predator control. Journal of Wildlife Management 36:395-400. Binning, L., and six coauthors. 1985. Pest management principles for the commercial applicator, aquatic pest control. University of Wisconsin, Cooperative Extension Service, Madison. Bradbury, A. 1986. Rotenone and trout stocking: a literature review with special refer- ence to Washington Department of Game's lake rehabilitation program. Washington Department of Game, Fisheries Management Report 86-2, Olympia.