100 r 



90 



o 



t 40 



30 



o 



^ 20 



_i 

 o 



X 



I*- 



0.2 



CHINOOK SALMON 



COHO SALMON 



RAINBOW - STEELHEAD TROUT 



0.5 

 VELOCITY (MPS.) 



0.8 



Figure 14. — Fish-collecting efficiency (mean percent) of the electrode array and array trap, 

 with the electrode array energized, for each water velocity and fish species. 



Figure 14 shows that the mean fisli-collecting 

 efficiency was highest for chinook salmon, inter- 

 mediate for coho salmon, and lowest for rainbow- 

 steelhead trout. 



Examination of table 3 shows that at the 0.2 

 m.p.s. velocity, the results were about the same in 

 the fourth test period as in the first three. At the 

 middle and high w ater velocities, however, the fish- 

 guiding and collecting efficiencies were substan- 

 tially lower during the fourth test period than 

 during the first three. To determine the reason for 

 this decrease, we considered such factors as the 

 size of fish, timing in the migration period, envi- 

 ronmental fluctuations, possible malfunctions of 

 the electronic equipment, and underwater damage 

 to the electrode array trap. None of these factors, 

 however, were sufficiently different from previous 

 conditions to provide an explanation for the lower 

 fish-guiding efficiencies. (It should be noted that 

 the sudden unexplained failures in fish guidance 

 at the middle and high water velocities did not 



occur at 0.2 m.p.s., which was the last velocity 

 tested during tlie fourth test period — see table 2.) 



ELECTRODE ARRAY NONENERGIZED PLUS 

 ARRAY TRAP 



We calculated the fish-collecting efficiency of the 

 electrode array and array trap with the power off 

 (table 4) for each test velocity and test period, by 

 fish species, by the same method used to determine 

 the fish-collecting efficiency of tlie electrode array 

 and array trap with the power on. The catches 

 compared were those made under control condi- 

 tions. Figure 15 shows that the fish-collecting effi- 

 ciency (mean percent) of the electrode array and 

 array trap with the power off increased for all 

 three species as the velocity increased. This in- 

 crease in fish-collecting efficiency with increasing 

 velocity during tests with the power off substan- 

 tiates one or both of our previous hypotheses that : 

 (1) the electrodes created hydraulic conditions at 

 the higher water velocities that diverted fish into 



320 



U.S. FISH AND WILDLIFE SERVICE 



