electromechanical barriers was operated. At its peak in 1959 the program 

 included about 135 barriers in the United States and Canada, but 401 of the 

 5,747 tributaries to the Great Lakes are known to produce sea lamprey. The 

 effectiveness of barriers as a control method was never adequately 

 determined, but there is no doubt that barriers are effective in killing 

 large numbers of adult sea lampreys. The barrier program was discontinued 

 as the major control method after the discovery of a selective chemical. 

 Electrical barriers are still used at selected sites as a means of 

 assessing program effectiveness and to provide control over experimental 

 areas. 



AB'MjR 



Figure 5. The Great Lakes. Numbers igdicate streams on which sea 

 lamprey counting weirs were installed. From Smith, 1971. 



Some 6,000 chemicals were screened through laboratory bioassay over a 

 7-year period (Applegate et al . , 1957). Promising toxicants were field 

 tested in 1957 and 1958. These successful tests led the commission in 1958 

 to adopt use of two chemicals, 3-trif luoromethyl-4-nitrophenol (TFM) and 

 2', 5-dichloro-4'nitrosalicylanilide (Bayer 73), as the major sea lamprey 



223 



