A Review of Fish Control Projects

We searched the fisheries literature to assess the success of fish control projects. We reviewed 250 control projects from 131 papers. Usually each treated body of water was considered a project. Fish control treatments were divided into four categories: chemical applications (145), physical removal and reservoir drawdowns (70), stocking of fish (29), and any combination of chemical and physical methods (6). Success was judged by changes in standing stock, growth, proportional stock density, relative weight values, catch or harvest rates, and other benefits, such as angler satisfaction. Reduction in standing stock was the most common determinant of success. Of the 250 projects, we considered 107 (43%) to be successful, 74 (29%) to be unsuccessful, and 69 (28%) to have insufficient data to determine success. The most successful projects targeted rough fish. Total elimination was more successful (63%) than partial reduction (40%) in 221 waters. Success was not strongly related to size of water body. Success of chemical application was similar for treatment with rotenone (48%) and with antimycin (45%). Success rates for physical removal methods (nets, traps, seines, electrofishing, drawdowns, and combinations of physical treatments) ranged from 33 to 57%. Stocking certain species of fish to control others was the least successful, 7 of 29 water bodies (24%). Combined chemical and physical methods were successful in 4 of 6 projects (66%). Stocking after chemical or physical treatment may have increased success of fish control projects; 10 of 17 such projects (59%) were successful, a higher percentage than for chemical treatments, physical treatments, or stocking alone. An overall success rate of less than 50% for such a large number and wide variety of projects indicates that there is considerable room for improvement of fish control projects. The large percentage of unsuccessful projects and the complexity of factors influencing fish communities suggest that control projects should include critical evaluation of assumptions and of suspected causes of problems, explicit rationale and objectives, and pretreatment and long-term posttreatment study.