EVALUATION OF THE RETURN OF ADULT CHINOOK SALMON 

 TO THE ABERNATHY INCUBATION CHANNEL 



Allan E. Thomas' 



ABSTRACT 



Adult returns of progeny of the 1964 year class of chinook salmon, Oncorhynchus tshawytscha, were 

 determined for the Abernathy incubation channel, natural production, and hatchery sources. A total of 

 4,620,600 fry were released from the channel into Abernathy Creek (state of Washington) as unmarked 

 fry. Natural production in the creek was estimated from spawning ground counts and fyke net 

 sampling of migrants at 16,700 fry, or 0.36% of the total unmarked fish. A total of 557,649 hatchery fish 

 were marked by feeding tetracycline, and 161,579 were both fin-clipped and fed tetracycline. All 2-, 3-, 

 and 4-yr-old adult fish returning to the hatchery holding pond were examined for fin clips and fluores- 

 cent bands on the vertebrae. Returns from hatchery sources were 506 fish or 0.070%. Potential egg 

 production was 865,000, or 76% of the original 1,142,604 eggs. Returns from the channel totaled 733 fish 

 or 0.016%. Egg potential was 2,050,000, or 35% of the original 5,888,048 eggs. Returns attributed to 

 Abernathy Creek totaled only three fish and egg potential was 0.2% of the original 2,880,000 eggs. 

 Survival of this year class was considerably below the 9-yr average of 0.118%. Intuitively, costs favor 

 incubation channel production over hatchery production. However, additional studies are needed to 

 determine if contributions to the fisheries and survivals are comparable in years of better year class 

 survival. 



Spawning and incubation channels for salmon 

 produce higher survivals of downstream migrants 

 than do natural spawning grounds. Studies by 

 Gangmark and Broad (1956), Lister and Walker 

 (1966), Thomas and Shelton (1968), and others have 

 shown that channels with flow and sediment con- 

 trol devices can produce many times as many 

 migrant-sized fish as are produced by the parent 

 stream. Little information is available on the per- 

 centage of fry produced in channels that return as 

 adults. Such data are needed to determine the 

 value of incubation channels for supporting and 

 maintaining salmon runs. 



In the present study, I compare the survival to 

 the adult stage of chinook salmon, Oncorhynchus 

 tshawytscha, from three sources: the Abernathy 

 incubation channel (near Longview, Wash.); the 

 Salmon-Cultural Laboratory hatchery adjacent to 

 the channel; and natural spawning in Abernathy 

 Creek. 



MATERIALS AND METHODS 



Problems were encountered in selecting the 

 techniques to use to distinguish returning adults 



'U.S. Fish and Wildlife Service, Fish Farming Experimental 

 Station, Stuttgart, AR 72160. 



from the various sources. Fin-clipping presented 

 two problems. First, fin-clipping of fry produced in 

 the channel was undesirable mainly because of the 

 small size of the fry (average weight, <0.5 g). The 

 chance of injury or incomplete removal of fins 

 would be high. Fin-clipping of hatchery fish has 

 been shown to reduce adult returns by 43.3% 

 (Weber and Wahle 1969). Second, the daily 

 numbers of fry migrating varied widely (from a 

 few thousand to over 120,000), depending upon 

 water conditions. Fin-clipping at a practical rate 

 would require that many fish be held beyond their 

 normal migration date. 



Marking channel and creek migrants with tet- 

 racycline would not be acceptable. Although 

 marking fish in this manner using techniques 

 developed by Weber and Ridgway (1962) had no 

 detrimental effect on adult survival (Weber and 

 Wahle 1969), the drug is normally administered in 

 the food. The artificial feeding of channel fish 

 might alter their characteristics and invalidate the 

 survival evaluations. Attempts to mark small fish 

 by immersion in solutions of tetracycline and 4% 

 dimethyl sulfoxide have shown some favorable 

 results (Richard C. Johnsen, pers. commun.), but 

 the technique has not been suflficiently developed 

 for reliable, large-scale marking. 



For these reasons migrant fry from the incuba- 

 tion channel and Abernathy Creek were not 



Manuscript accepted July 1974. 



FISHERY BULLETIN:VOL. 73, NO. 2, 1975. 



356 



