to a depth of more than 8 feet. In this area 

 they were subjected to voltages ranging from 

 0.42 to 0.54 volts per inch. With higher stream 

 velocities the depth of penetration was probably 

 less but accurate observation was difficult. 

 The length of the field determines the time of 

 exposure with all other conditions equal. Less- 

 er voltages, therefore, are required as the 

 field length is increased. 



Salmon subjected to a voltage gradient of 

 not more than 0.75 volts per inch do not suffer 

 tetanus even though prolonged exposure results 

 in immobilization and eventual death . Higher 

 voltages, however, do cause acute muscular 

 spasms severe enough to dislocate the verte- 

 brae. Surprisingly enough, fish which survive 

 such shocks do not seem to be seriously in- 

 capacitated and despite a spinal curvature are 

 capable of swimming effectively. It is desir- 

 able, however, that severe shock be avoided. 



In a weir of the Entiat type, high voltages 

 exist adjacent to the electrodes. At a distance 

 of 6 inches from the electrodes the measure- 

 ment is 2 volts per inch, but high voltages are 

 of little significance provided the field is of suf- 

 ficient length and strength to prevent the fish 

 from penetrating far enough to approach the 

 electrodes. In areas of shallow water, under 

 4 inches in depth, the electrical field is greatly 

 distorted both by diversion of the electrical cur- 

 rent through the ground and any unevenness of 

 the stream bottom . In such areas the voltage 

 gradient is more acute and the pattern is erratic . 

 Under these conditions salmon may occasionally 

 penetrate the field to within 1 or 2 feet of the 

 electrodes where they are subjected to voltages 

 sufficiently high to cause vertebral dislocations. 



The unfavorable conditions in shallow 

 water areas of the electrical field are usually 

 aggravated by a reduced water velocity. These 

 conditions were corrected at the Entiat site by 

 recessing the ground line to create a faster 

 water velocity and allow the fish free egress 

 from the field. In addition as shallow areas 

 were created by dropping river levels the fish 

 were diverted from these areas by the use of 

 rock dikes. Obviously the use of abutments to 

 constrict the stream flow would eliminate this 

 problem but, in locations where low stream 

 banks make abutments impossible, the use of an 



electrical weir is not precluded providing the 

 proper precautions are taken. 



Large rocks within the electrical field 

 must be avoided for they disrupt both the water 

 velocity pattern and the voltage gradient. High 

 voltages occur in areas adjacent to boulders, 

 and eddies are created behind them . Fish which 

 encounter the high voltage adjacent to a large 

 rock may be stunned and either swept against 

 the boulder or held in the eddy behind it until 

 killed. 



Characteristics of the electrical field 

 created by this type of weir are particularly 

 adapted to the diversion of salmon . The primary 

 requirements of adequate stream velocities and 

 an electrical field of sufficient strength and 

 length to halt the upstream progress of the fish 

 are not impossible to attain in most Pacific 

 Coast streams containing salmon runs. The 

 exact size limitations both as to the length of 

 the weir and the depth of water in which it will 

 op)erate effectively are not known. The present 

 test installations have been confined to water 

 depths less than 8 feet and to weir lengths under 

 200 feet. 



REACTIONS OF SALMON TO THE 

 ELECTRICAL FIELD 



Both Chinook and sockeye salmon runs 

 have been under direct observation at the Entiat 

 weir site since 1953. From these observations 

 it has been possible to ascertain the reactions of 

 these species to the electrical field. 



Chinook salmon "learn" readily. How 

 many times a fish will penetrate the field is dif- 

 ficult to ascertain because on their first encounter 

 the fish move rapidly downstream for about 200 

 yards and their individual identities are lost. 

 Observation indicates, however, that after one 

 or more experiences with the weir, chinook 

 recognize and avoid the electrical field. They 

 are sensitive to less than 0. 1 volt per inch as 

 indicated by the collection of fish just below the 

 ground line where voltages vary from 0.05 to 0.1 

 volts per inch. It is at this stage, when they 

 have become conditioned to an electrical stimulus, 

 that the angle lead of the weir becomes effective 

 in directing the fish toward the fish ladder. 



8 



