Laboratory Tests of an Electrical Barrier for 

 Controlling Predation by Northern Squawfish 



By 



GALEN H. MAXFIELD, ROBERT H. LANDER, and CHARLES D. VOLZ 



Fishery Biologists 



Bureau of Commercial Fisheries Biological Laboratory 

 Seattle, Washington 98102 



ABSTRACT 



Northern squawfish ( Ptychocheilus oregonensis ) prey extensively on the young 

 of sport and commercial fishes. Of particular concern to us was their heavy preda- 

 tion during early spring and summer on salmon ( Oncorhynchus spp.) that are 

 released from upstream hatcheries on the Columbia River and must pass through 

 squawfish-infested areas on their way to the sea. Control of these predators entailed 

 finding a means of blocking their passage into the release areas of the hatchery- 

 reared salmon without interfering with the outmigration. For this purpose, we 

 explored in the laboratory the effectiveness of electrical fields previously found to 

 direct the movements of salmon fingerlings. 



Electrical fields were produced by two rows of hollow aluminum electrodes 

 suspended in the water across a laboratory tank. Exploratory tests were run to 

 determine what combinations of electrode arrays, voltage gradients, and electrical 

 conditions would give results warranting systematic testing. Ten fish were 

 tested individually in each of these elimination tests. 



On the basis of test results, four electrode arrays, with capacitor discharge 

 pulses at 8 pulses per second and a pulse duration equivalent to that of 40 milli- 

 second "rectangular pulse," were tested at three voltage gradients. A staggered 

 array of electrodes in which the electrodes were spaced at 6l-cm. intervals in 

 rows 200 cm. apart was most effective. At the voltage gradients of 0.75, 1.00, and 

 1.25 volts per centimeter, 85, 93, and 96 percent respectively, of the squawfish 

 were blocked. 



INTRODUCTION 



The northern squawfish, a fresh-water spe- 

 cies in streams and lakes, has been widely 

 reported to prey on the young of Pacific 

 salmon, One o r hync hu s spp., and other de- 

 sirable sport and food fishes (see, for example, 

 Carl and Clemens, 1948; Foerster, 1937, 1938; 

 Foerster and Ricker, 1941; and Ricker, 1941). 



In the lower Columbia River, predation by 

 adult northern squawfish on salmon fry and 

 fingerlings from hatcheries has been noted in 

 the areas of release (Thompson, 1959). Ex- 

 tensive predation has been observed at the 

 Little White Salmon station on the Little White 

 Salmon River, about 1.6 km. above its con- 

 fluence with the Columbia River (fig. 1). The 

 construction of Bonneville Dam resulted in the 

 inundation of the lower half of Little White 

 Salmon River and the formation of an embay- 

 ment that is now referred to as Drano Lake. 



Predation is particularly extensive while 

 hatchery fish are passing through this lake. 1 



In 1953 we set gill nets to determine the 

 abundance and movements of northern squaw- 

 fish in Drano Lake before and during releases 

 of fry and fingerlings of chinook salmon, 

 0_. tshawytscha , into the lake. Catches demon- 

 strated that the population of squawfish was 

 fairly stable during February and April but that 

 squawfish moved into the lake from the Colum- 

 bia River during May and June, after the hatch- 

 ery releases. Thus, controlling the squawfish 

 would involve not only the reduction of the winter 

 population, but also the control of their immi- 

 gration into Drano Lake from the Columbia 

 River during the period of hatchery releases. 



Zimmer, Paul D. 1953. Observations on hatchery re- 

 leases and squawfish predation in Little White Salmon 

 River in spring of 1953. U.S. Fish Wildl. Serv., Portland, 

 Oreg., 14 pp. [Processed.] 



