DIVERSION OF ADULT SALMON BY AN ELECTRICAL FIELD 



INTRODUCTION 



The artificial propagation of salmon, un- 

 like that of trout, is dependent, entirely, on 

 the entrapment of wild fish as a source of eggs. 

 Because of this dependency, the trapping and 

 retention of the adult fish until maturity is one 

 of the primary problems in salmon culture. 

 The problem becomes particularly acute in 

 some species of salmon where the interval be- 

 tween the upstream and spawning migrations 

 may be as long as three or four months. Un- 

 less natural holding facilities such as lakes 

 exist which cause the fish to remain concen- 

 trated until the spawning migration, the salmon 

 must be captured on the upstream migration to 

 prevent dispersal throughout the river system . 



The confinement of the fish until maturity 

 creates still another problem. The use of 

 stream impoundments has proved unreliable 

 because they are subject to the vagaries of sea- 

 sonal stream flows which may destroy or bypass 

 the retaining racks and permit the escapement 

 of the entire spawning stock. A loss of such 

 magnitude can be catastrophic to a program of 

 artificial propagation for the production poten- 

 tial for an entire year may be lost . Artificial 

 holding areas with controlled water supplies 

 have proved much more reliable for the reten- 

 tion of the fish. With at least a partial solution 

 to the impoundment problem available, actual 

 diversion of the adult migration either into 

 traps or into artificial holding areas becomes 

 the critical factor in the procurement of the fish. 



Conventional methods for diversion of 

 salmon employ mechanical barriers of one sort 

 or another to halt upstream progress of the fish 

 and force them to seek another route . Such 

 barriers usually impede stream flow and either 

 become ineffective or are destroyed at high 

 water stages. They are costly to install and 

 difficult to maintain under most conditions and 

 cannot be classed as positive barriers. 



In the search for a positive method of 

 diversion the use of an electrical field has been 

 at least partially explored. Until the problem 



of sea lamprey control in the Great Lakes de- 

 veloped, the primary interest in the use of 

 electrical barriers was for the diversion of 

 downstream migrants. The history of these 

 early experiments has been reviewed by Holmes 

 (1948). The Great Lakes Fishery Investigations 

 of the U. S. Fish and Wildlife Service, faced 

 with the problem of controlling the sea lamprey, 

 explored the possibilities of electrical fields 

 both for the diversion of upstream migrants 

 and as lethal devices. The results of these ex- 

 periments using alternating current were 

 reported by Applegate , Smith, and Nielsen (1952) 

 and using direct current by McLain and Nielsen 

 (1953). The conclusion drawn from these in- 

 vestigations was that an electrical field created 

 by 110 -volt, 60-cycle, alternating current was - 

 the most effective method for the diversion of 

 upstream migrants. 



The results of these investigations were 

 utilized in the development of an electrical bar- 

 rier for the diversion of adult salmon. Upon the 

 recommendation of Mr. Bernard R. Smith of the 

 Great Lakes staff, the alternating current field 

 created by a single row of hanging electrodes 

 and a ground line was selected as the most suit- 

 able for the stream conditions to be encountered 

 at the Salmon -Cultural Laboratory. This in- 

 stallation, with some alteration, has been tested 

 since 1953 as a method for the diversion of adult 

 salmon. It has been found to be a positive bar- 

 rier and an excellent method for the diversion 

 of adult salmon. This report will be concerned 

 with a general description of this type of weir, 

 the factors influencing its efficient operation, 

 the reaction of salmon to the electrical field, and 

 the application of the weir in salmon culture . 



DESCRIPTION OF THE WEIR 



The requirements of an electrical field 

 for the diversion of adult salmon differ consider- 

 ably from those for the trapping and destruction 

 of sea lamprey. Salmon, being larger, are more 

 sensitive to an electrical field and therefore re- 

 quire a lower minimum voltage to provide a 

 positive barrier . Because they are larger the 

 momentum acquired before entering the field is 



