LEADING ADULT SQUAWFISH ( PTYCHOCHEILUS OREGONENSIS ) 

 WITHIN AN ELECTRIC FIELD 



by 



Galen H. Maxfield, Kenneth L. Liscom, and Robert H. 

 United States Fish and Wildlife Service 

 Seattle, Washington 



Lander 



ABSTRACT 



The nature of squawfish predation on hatchery -reared salmon fingeriings requires an economical 

 and practical method for continuously removing the squawfish from the areas of releases. Research has 

 been directed toward the development of an electrical trapping device employing the principle of elec- 

 tiotaxis. The objectives of the study were to determine by systematic testing, (A) the optimum values 

 of the electrical variables of (1) potential (60, 75, and 90 volts), (2) pulse frequency (2, 5, and 8 pulses 

 per second), and (3) pulse duration (10, 20, and 30 milliseconds) for leading adult squawfish within an 

 electrical array; and (B) the possible significance of the direction of movement of the electrical fields. 

 Pulse frequency was found to be the most critical variables (optimum, 2 pulses per second). Potential 

 was also significant (optimum, 60 volts), but pulse duration was not significant, at least in the range 

 tested. The direction of the electrical fields io tiie laboratory tank was a highly significant variable. 

 The fi'!>i showed a greater response when the electrical fields moved toward the north end of the labora- 

 tory tank than toward the south. The reason for this reaction was not determined. 



INTRODUCTION 



For the past five yceirs, the Columbia 

 River fishery for salmon and steelhead has 

 been valued at $17,000,000 annually. In 

 addition, this fishery has provided an 

 inestimable amount of pleasure to sports 

 fishermen. The fishery is sustained, in 

 part, by some 600,000 Columbia River salmon 

 and steelhead that annually ascend the fish 

 ladders at Bonneville Dam. However, reduc- 

 tion in spawning areas, due to construction 

 of dams, has caused increasing dependence 

 on hatchery-reared fish. 



In 1956, about 58,000,000 salmon fin- 

 geriings, reared in hatcheries at a cost of 

 $732,000, were released into the Columbia 

 River and its tributaries below McNary Dam. 

 Since the fingerling salmon are released in 

 dense concentrations, thus becoming easy 

 prey for predatory fish, the success of the 

 salmon-rearing program is greatly affected 

 by the predators. Biologists and hatchery 

 personnel have often observed at times of 

 release of fingerling salmon that the squaw- 

 fish ( Ptychocheilus oregonensis (Richard- 

 son) , is the most destructive of these 

 predators. 



A study by the U. S. Fish and Wildlife 



Service — has shown that almost all of the 

 predation by squawfish occurs immediately 

 after release of the fingeriings. This fact 

 indicates that the most effective way to 

 control Squawfish predation is to reduce the 

 numbers of squawfish in the areas where the 

 fingeriings are released. 



Management biologists have used dyna- 

 mite and gill nets to reduce the populations 

 of resident squawfish in the release areas 

 for periods of several weeks prior to the 

 release of the fingeriings. Neither of 

 these control measures has been effective, 

 however, as the release of fingeriings soon 

 attracts more squawfish.—' Once the fin- 

 geriings are released, dynamite no longer 



V Thompson, Richard B. Food of the 

 squawfish, Ptychocheilus oregonensis 

 (Richardson), of the Lower Columbia 

 River. United States Fish and Wildlife 

 Service. Fish. Bull. No. 158 (In press) 



£/ Zimmer, Paul D. Observations on hatch- 

 ery releases and squawfish predation in 

 Little White Sailraon River in spring of 

 1953. United States Fish and Wildlife 

 Service, Mimeo. Report, August 1953. 

 14 pp. Portland, Oregon. 



