FISHERY BULLETIN: VOL. 72, NO. 3 





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Table 3. — Effective electrical combinations based on a mini- 

 mum of 70% eliciting a positive response (Group 1 fish). 



fish. The wild fish were only exposed to a pulse 

 width of 0.5 ms, as the time between tests did 

 not permit a change in pulse width. Since this 

 pulse width provided satisfactory results, we felt 

 that either 0.5 or 0.8 ms would be satisfactory, 

 as indicated from our captured fish experiments. 

 Visual observations indicated that the larger 

 fish (>10 cm) reacted more quickly and swam to 

 and from the anode before the smaller fish 

 (<10 cm) did. Table 4 provides details and sum- 

 maries of our nighttime observations with wild 

 fish. In general, Spanish sardines and round scad 

 were controlled adequately at 120 V and a pulse 

 rate of 25 to 35 pulses/s at a pulse width of 

 0.5 ms. When large schools were attracted 

 between the electrodes, it was not always pos- 

 sible to control all of the animals. Our visual 

 observations indicated that fish in the fringe area 

 would escape since the voltage gradient was insuf- 

 ficient to control fish in the fringe areas. The 

 number offish escaping probably varied with their 

 position in the electrical field and their size, 

 since smaller fish require higher voltage gradi- 

 ents for control than large fish. At 35 pulses/s 

 and 120 V, we were able to pull or force fish into 

 the electrode array from the back side of the posi- 

 tive electrode. Positive reactions were elicited in 

 all species at the prime voltage of 120 and pulse 

 rates between 25 and 35. The results from the 

 wild fish experiment conclusively demonstrate 

 that coastal pelagic fish of the species tested can 

 be controlled and led with combinations of 

 120 V, 25 to 35 pulses/s, and a pulse width of 0.5 ms. 



DISCUSSION 



Effective electrical combinations for controlling 

 coastal pelagic species determined during our field 

 experiments compared favorably with the param- 

 eters determined by Klima (1970) in labora- 



662 



