FISHERY BULLETIN: VOL. 72, NO. 3 



Using Equation (7) at 15 V/m, the range of an 

 electrode is: 



R 



[2,250 X 1 X 0.189 

 15 X 2 X 3.14 



R = 2.13 m. 



However, to accomplish at least a fright 

 reaction required 10 V/m or less, depending on fish 

 size. We feel that a fright reaction, although not as 

 effective as positive control offish, will accomplish 

 disorientation and therefore harvest of some fish 

 in an electrical trawling mode. Since the tem- 

 perature of below-surface water will be colder, 

 we can use higher resistivities than 0.189 in 

 calculations as shown in the following calculation 

 for field reach at 100 fm water depth. In addition, 

 Kreutzer's Equation (7) states that the factor 

 in the denominator goes from 2 to 4 as the 

 electrodes are placed in mid-water. Using these 

 values, we calculate the maximum variation of 

 values from the surface to 100 fm in the 10 

 V/m range of one electrode to be: 



Surface: 

 Salinity 32.9%o, temperature 28.7°C, 

 p = 0.189 



R = 



2,250 X 1 X 0.189 

 10 X 2 X 3.14 



R = 2.60 m. 

 100 fm: 



Sahnity 30 °/oo, temperature 10°C, P= 0.3 



R = 



/2,250 X 1 X 0.3 

 10 X 4 X 3.14 



R = 2.32 m. 



Again, the range of two electrodes is found to be 

 greater than twice the range of one electrode. In 

 addition, since each electrode pair based on their 

 required size for 0.2 ohm, will be separated 

 by about 1.22 m, field strength adding will occur. 

 Therefore, the effective range of an electrode pair 

 is significantly more than twice the range of one 

 electrode. By installing one polarity electrode on 

 the headrope and the opposite on the footrope, we 

 should be able to cover a 9 x 9 m area with 



the weakest part of the field having at least 

 enough strength to frighten fish. We can also use 

 pulse rates higher than 35/s, which will immobi- 

 lize fish more rapidly. In addition, it must be 

 remembered that at distances closer to the 

 electrodes, the field strength increases and 

 reaches values which will effectively lead or stun 

 the fish. Because the size of each electrode is 

 relatively small, current densities capable of stun- 

 ning fish will be found at some minimum distance 

 from the electrodes. This is not desirable for 

 leading fish in a netless harvesting application 

 and is avoided by using large electrodes, but it is 

 very desirable in a trawling mode where the 

 electrodes are inside the body of the net. 



ACKNOWLEDGMENTS 



We are grateful to Harvey R. Bullis, Jr. for 

 his support and continual encouragement of this 

 project. Conradin Kreutzer was of invaluable 

 assistance with his expert advice, technical 

 knowledge of physics and electricity, and design 

 experience in constructing the pulse generator 

 and experimental hardware. 



LITERATURE CITED 



Bary, B. M. 



1956. The effect of electric fields on marine fishes. Scotl. 



Home Dep. 1, 32 p. 



Bullis, H. R., Jr., and J. R. Thompson. 



1970. Bureau of Commercial Fisheries Exploratory Fish- 

 ing and Gear Research Base, Pascagoula, Mississippi, 

 July 1, 1967 to June 30, 1969. U.S. Fish Wildl. Serv., 

 Circ. 351, 29 p. 



Collins, G. B., C. D. Volz, and P. S. Trefethen. 



1954. Mortality of salmon fingerlings exposed to 

 pulsating direct current. U.S. Fish Wildl. Serv., Fish 

 Bull. 56:61-81. 



Halsband, E. 



1967. Basic principles of electric fishing. In R. Vibert 

 (editor), Fishing with electricity- Its applications to 

 biology and management, p. 57-64. Fishing News (Books) 

 Ltd., Lond. 



Higman, J. B. 



1956. The behavior of pink grooved shrimp, Penaeus 

 duorarum Burkenroad, in a direct current electrical field. 

 Fla. State Board Conserv., Tech. Ser. 16, 23 p. 

 Kessler, D. W. 



1965. Electrical threshold responses of pink shrimp 

 Penaeus duorarum, Burkenroad. Bull. Mar. Sci. 

 15:885-895. 

 Klima, E. F. 



1968. Shrimp-behavior studies underlying the develop- 

 ment of the electric shrimp-trawl system. U.S. Fish. 

 Wildl. Serv., Fish. Ind. Res. 4:165-181. 



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