p 100 



S 901- 

 cr 



0. 8 h . M 



Q 70 



UJ 

 OL 



% 60 



q: 



»- 50 



I 40 

 u. 



< 30 



3 

 O 



(n 20 



10 









rrrrr 





July 2-15 

 POWER ON OFF 



July 16-21 

 ON OFF 



July 22-27 

 ON OFF 



July 26-31 

 ON OFF 



Figure 8. — Percentage of squawfish trapped in four series of 48-hour tests, 24 hours "power on" and 24 hours "power 



off," July 2 to Aug. 1, 1958. 



Chi-square was significant (p<0.01); there- 

 fore, we concluded that the squawfish were 

 diverted by the electric fields. 



For each of the four test series, we sub- 

 tracted the "power off" catches from the 

 corresponding "power on" catches (table 4); 

 these figures estimate the numbers trapped 

 under the influence of electricity. To examine 

 the relative effect of electricity during the 

 four series, we then divided these estimates 

 by the "power on" catches and tested the 

 fractions for uniformity. The fraction trapped 



under the influence of electricity was signifi- 

 cantly smaller (p<0.01) for the test series 

 July 16-21. Thus, the data suggest that the 

 effectiveness of the electrical fields in trapping 

 squawfish is decreased when the pulse fre- 

 quency exceeds some value between 10 and 15 

 pulses per second (2 and 3 pulses per field 

 per second, respectively, when five fields 

 were pulsed in sequence) or when the pulse 

 duration is shortened below some value be- 

 tween 30 and 50 msec. 



13 



