FiQUBE 13. — Troughs for counting anid identifying salmon and trout. 



14). The decrease in fish-collecting efficiency be- 

 tween 0.2 and 0.5 m.p.s. and the increase at 0.8 

 m.p.s. suggests that fish-guiding efficiency de- 

 creased as tlie water \elocity increased, but that 

 perliaps : ( 1 ) tlie electrodes created hydraulic con- 

 ditions that diverted more fish into the array trap 

 at a water velocity of 0.8 m.p.s. than at 0.5 m.p.s. or 

 (2) that the fish-holding efficiency of the array- 

 trap was higher at 0.8 m.p.s. than at 0.5 m.p.s. It 

 was not possible within the scope of this research 

 to determine the efl'ect of the hydraulic conditions 

 created by the electrodes on the fish-guiding 

 efficiency of the electrical system, nor was it pos- 

 sible to determine conclusively the holding effi- 

 ciency of tlic array trap at each of the three test 

 velocities. Because salmon and trout populations 

 of the Yakima River at the time of this experiment 

 were so critically low, we deemed it inadvisable to 

 handle, mark, and delay the number of migrating 



salmon and trout required to determine accurately 

 the efficiency of the array trap in retaining fish. 



General observations, however, indicated that 

 fish could escape from the array trap at all test 

 velocities but that fish-iiolding efficiency was 

 higher at 0.5 m.p.s. and at 0.8 m.p.s. than at 0.2 

 m.p.s. Therefore, during the power-on tests, some 

 fisli were probably guided into the array trap by 

 the electrical system but, because they were not 

 removed immediately, they were able to escape by 

 swimming back upstream into the canal. Conse- 

 quently, all of the fish-guiding and collecting 

 efficiencies reported here for the low and middle 

 water velocities are probably lower than the actual 

 efficiencies achieved. Those reported for the highest 

 water velocity, 0.8 m.p.s., are probably more ac- 

 curate than those for the lower velocities, but even 

 these values are doubtless below the actual values 

 achieved. 



FISH-GUIDING EFFICIENCY OF AN ELECTRICAL GUIDING SYSTEM 



319 



I 



