randomly distributed within the schools 

 of passing fish, and it was desired to 

 determine the efficiency of capturing any 

 specific fish that nnigrated upstream. 



Electrodes were panels of screening, 

 3 feet wide and 8 to 25 feet long, installed 

 flat on the river bottom in the usual path 

 of migrating fish. The negative electrode 

 was in the offshore position; the positive 

 electrode, to which fish are attracted by 

 the pulsing direct current, was closer to 

 shore. As the selected tagged fish passed 

 between the electrodes the current was 

 turned on, forcing the fish towards the 

 positive electrode, where, in the denser 

 electrical field, it was narcotized in a 

 more accessible position in shallow, 

 quieter water. Final capture was accom- 

 plished with a long-handled dip net. It 

 was possible to allow the remainder of 

 the school to escape unharmed, for direct 

 current causes no harm unless fish are 

 burned by direct contact with the elec- 

 trode. 



The object was to move a specific fish 

 into the vicinity of the positive electrode 

 by means of the pulsing current (elec- 

 trotaxis) and to immobilize or render it 

 unconscious (electronarcotized) in the 

 immediate vicinity of the positive elec- 

 trode. 



The equipment necessary for this op- 

 eration consists of a portable generator 

 (as a power source), pulsing and current- 

 control unit, lead wires to the electrodes 

 from the pulser, the electrodes them- 

 selves, and a long-handled dip net or spear 

 to make the final capture. 



The generator used was a modified 

 Homelite Model 24D230, which produced 

 2,500 watts of direct current at 230 volts. 

 The generator has been modified with 

 capacitors and resistors to match its out- 

 put to the Type HI transitorized pulsing 

 and control unit of the Fish and Wildlife 

 Service. 



The Type III pulser and control unit 

 was produced for the Predator-Competitor 

 Investigations by the Fisheries Instru- 

 mentation Laboratory, both located at the 

 Seattle Biological Laboratory, Bureau of 

 Commercial Fisheries, U.S. Fish and 

 Wildlife Service. The transistorized pulser 



is an elaborated version of the Type 11 

 pulser described by Dale.' This pulser 

 produces square-wave pulsations of direct 

 current at 230 volts. Frequencies of pulsa- 

 tion adjustable from 2 to 200 per second 

 are available. Duty cycles, that is, the 

 percentage of on-time within a full pulse, 

 are available between 30 and 90 percent. 

 Superposition of a high-cycle pulsation and 

 a low-cycle pulsation results in bursts of 

 pulses or double modulation of the pulse 

 pattern. 



A remote push-button control switch is 

 provided to operate the pulse unit to send 

 the pulsed current to the electrodes. Re- 

 leasing the button opens the control circuit 

 and turns off the currentto the electrodes. 



The fish shocker apparatus was first 

 installed on the north bank of the Kvichak 

 River, 100 yards upstream from the Insti- 

 tute's No. 1 counting tower. The electrodes 

 extended out into the river perpendicular 

 to the bank from where the depth of water 

 was about 3 feet to where it was 8 feet 

 deep, a distance of about 30 feet. The 

 negative electrode was placed downstreann 

 of the positive electrode so that there 

 was a distance of 10 feet separating the 

 two. These electrodes were laid flat on the 

 river bottom under the path of the salmon 

 migration. 



At this location it was necessary to 

 have at least a 3 -man crew for optimum 

 operation. From an elevated position 

 where he could observe the fish, one man 

 operated the push button that energized the 

 electrodes. In a boat, one man attempted 

 to capture the narcotized fish with a dip 

 net upon signal from the operator while 

 the other controlled the boat. 



At camps where counting stations have 

 been operated, manpower availability is 

 usually limited. With this in mind, another 

 location was sought where one man could 

 operate the entire collecting system; that 

 is, observe the passage of fish, operate 

 the generator and pulsing unit, and make 

 the recovery of the tagged fish. 



The site was located just below a small 

 eddy which was formed by the main river 

 current flowing around a small rocky point 

 (fig. 2). The migration path of the salmon 

 followed within 10-15 feet of the shoreline 



3Dale, Harry P. Electronic fishing with underwater pulses. 

 Electronics, vol. 32, No. 4, pp. 31-33, January 1959. 



