smaller numbers of salmon in the 1963B re- 

 lease, the percentage of this release lost was 

 almost three times greater than that for 1963A. 



The average length of salmon recovered 

 from stomachs of sculpins was smaller than 

 the average length of those released. The 

 mean length of the salmon released from the 

 Elokomin Hatchery was 59 mm. in 1962 and 

 60 mm. in 1963; lengths of salmon from 

 stomachs of predators averaged 43 mm. in 1962 

 and 42 mm. in 1963 (differences were similar 

 in Herman Creek). Also, the more capable 

 salmon predator, prickly sculpin, fed on the 

 same sized prey as smaller species of sculpins. 

 It seems clear that the sculpins preyed selec- 

 tively on the smaller salmon in the releases. 



The hatchery salmon varied in alertness 

 and agility between 1962 and 1963. The 1962 

 and 1963 releases of chinook salmon fry and 

 wild coho salmon fry differed in their ability 

 to evade capture in the stream by a dipnet. 

 It was more difficult to catch chinook salmon 

 in 1963 than in 1962; it was almost impossible 

 to capture wild coho salmon fry in either year 

 by this method. Chinook salmon released in 

 1962 were not as responsive to movements 

 above the surface as those liberated in 1963, 

 which instantly sounded at slight movements 

 above the surface. The greater alertness and 

 agility of the salmon in 1963 may have con- 

 tributed to the less intense predation in that 

 year than in 1962. 



By Salmon and Trout 



Although the primary aim of my study was 

 to examine predation by sculpins on fry of 

 chinook salmon, I examined stomachs of some 

 trout and yearling coho salmon collected in 

 the Elokomin River after the releases of chi- 

 nook salmon fry in 1963 (one rainbow trout 

 was collected in Herman Creek in 1962). 

 Salmon were found in the stomachs of 3 of 58 

 yearling coho salmon, in 11 of 44 rainbow 

 trout from the Elokomin River, and in 14 of 

 27 cutthroat. Tables 6, 7, and 8 show the in- 

 cidence, rate, and maximum numbers of salmon 

 eaten by salmon and trout predators. The rain- 

 bow trout from Herman Creek had eaten three 

 salmon. 



INFLUENCE OF 



HATCHERY TECHNIQUES ON 



SALMON LOSS 



The damage by fish predators to chinook 

 salmon fry released in the Elokomin River was 

 rather extensive. The extent of this damage 

 from the predatory activities of certain stream 

 fishes depends partly on the availability and 

 susceptibility of hatchery fish. Controlling the 

 predators might reduce the damage. The cost 

 of control of sculpins, however, is difficult to 

 justify, and attempts to control predation at 

 an early point in the life of salmon in poor 

 condition would be of little value because the 

 pressures of survival would surely eliminate 

 them later. If cultural practices were known 

 to be developed to a point where the quality of 

 the fish approached the maximum attainable 

 and heavy predation still continued, predator- 

 control measures would be worth considering. 

 Because hatchery practices are still improving, 

 it is not justifiable now to recommend control 

 measures on fresh-water sculpins or other 

 predatory fish. Indeed, predation on hatchery 

 salmon has always been a major concern of 

 fish-culturists and the results of this study 

 provide data that are important for the im- 

 provement of techniques of culture and release 

 of salmon. 



Factors Related to Methods of 

 Fish Culture 



Cultural techniques that better enable salm- 

 on to cope with the natural environment are 

 clearly desirable, as salmon released from 

 hatcheries will always be exposed to many 

 predators. Good physical condition and large 

 size are recognized as qualities for which 

 culturists should strive. 



Fitness of hatchery salmon may be attained 

 by physical conditioning and proper diets. Sur- 

 vival of hatchery fish has been improved by 

 exercising (Burrows, 1964) and by predator- 

 avoidance conditioning (Thompson, 1966"). 

 Data from this paper lend support to the hy- 

 pothesis that proper diets can decrease losses 

 from predation. 



3 Richard B. Thompson. 1966. Effects of predator 

 avoidance conditioning on the post-release survival rate 

 of artificially propagated salmon. Ph.D. Thesis, Univ. 

 Wash., Seattle, 155 pp. Typescript. 



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