DISCUSSION • 



The results of these exploratory experiments generally agree with the results 

 of other investigators. Lethlean (1^53) noted that he expected better results by in- 

 creasing the angle of the lines of electrodes in relation to the dam from 30° to 45° . 

 Biologists of the International Pacific Salmon Fisheries Commission were quite 

 successful at Cultus Lake (1953) in diverting salm.on fingerlings with an angle of 

 45° and a 2 -foot width of field. 



In the experiments under the laboratory conditions described, a maximum per- 

 centage was recovered in the narrow channel with the rows of electrodes spaced 2 

 feet apart. When the v/idth of field was increased to 3 feet the .effectiveness was 

 reduced and it was observed that many fish experienced difficulty in escaping an area 

 in the immediate vicinity of a positive electrode. At the same time other fish were 

 paralyzed in the electrical field and were carried through it by the water current 

 untii they recovered equilibrium beyond the field. These factors are probably the 

 cause of much of the scatter in the data resulting from the 3 -foot width of field; 

 they are possibly the result of the increased power necessary to maintain the average 

 voltage gradient of 1 volt/cm. McMillan (1928) pointed out that when the distance 

 between rows of electrodes was increased while maintaining a constant voltage grad- 

 ient ihe concentration of the voltage gradient at the surface of the electrodes increased. 



Tests run under full light intensity resulted in a slight increase of the effective- 

 ness. A further increase was obtained when large numbers were released under full 

 light intensity. The results of these preliminary experiments Suggest that group 

 movement may be an important factor in diverting salmon fingerlings . When large 

 schools migrate downstream into an electrical field the effectiveness may be hi^er 

 than when smaller groups come in contact with d.c- barrier. Okada (1929) observed 

 that a weaker field can restrain the same percentage of fish as a stronger one when 

 the group was composed of many fish, indicating that group movement was involved in 

 his experiments. 



Since full-scale field trials were scheduled to begin subsequent to the completion 

 of these laboratory experiments, the experiments were limitfed to three angles, two 

 diameters of electrodes, a single field, and one arrangement of electrodes. The 

 experiments were conducted within a range of terriperatures of 8°C,, ,with a maximum 

 temperature of 16° C . Two test and two control experiments were uSed to investigate 

 any one set of conditions; each point on the preceding graphs was established with 

 approximately 100 fish. Hatchery -reared silver salmon ranging in size from 5.5 cm. 

 to 12.0 cm. were used; this does not include the range of sizes or species that would 

 be encountered under natural conditions . Another factor to be considered is that wild 

 fish may be more or less sensitive to an electrical field than?;hatchery -reared fish. 

 However, the experiments show the relative effectiveness of the various factors exam- 

 ined in this type of narrow d.c. ireld employed as a diverting barrier. 



39 



