41 



rable 14. Dilution effects en the ger.e pool of Snake River fall cr.L-czk 

 salmon labeled as "natural spauners" prior to 1983 due to estimated 

 numbers of strays entering into the escapements since 1983 under 

 various assumptions concerning the "fitness" of the two types of 

 strays. ^ 



Estimated Proportion of the Gene Pool Composed of "Natural Spawners"' 

 (heading abbreviations: (N) = "naturals; (S) = stravs; F = "fitness" 



Snake River and Columbia River Only Columbia R. Strays 



Stravs Included in the Stray Category Included as "Stravs" 



F(N) - 1.0 FCN) - 1.0 F(N) - 1.0 F(N) - 1.0 F{N) . 1.0 



F(S) ■ 0.0 F(S) . 0.5 F(S) = 1.0 F(S) - 0.5 F(S) ~ 10 



100% 100% 100% 100% 



100% 100% 100% 100% 



100% 100% 100* 100% 



100% 100% . 100% 100% 



100% 100% 100% 100% 



100% 100% 100% 100% 



100% 100% 100% 100% 



100% 100% 100% 100% 



88% 79% 100% 100% 



67% 51% 100% 99% 



78% 63* 99% 98% 



70% 54* 99% 99% 



35% 20* 97* 94% 



54% 34* 95* 90% 



44% 25* 83* 70% 



23% . 10* 85* 75% 



32% 16* 92* 85% 



44% 24* 91* 85% 



34% 17* 78* 62% 



24% 10% 



The simple dilution model used to derive these estimates assumed the gene 

 pool was 100% "natural spawners" prior to 1983 when coded wire tag data 

 technology first provided estimates of hatchery strays passing Lower Granite 

 Dam. The model assumes random mating; stray rates as defined in Table 4 

 were used; age composition of escapements were assumed as follows: 30% age 

 3, 56% age 4, and 14% age 5. A fitness value of 1 . assumes that strays 

 reproduce as successfully as "naturals". A fitness value of 0.5 assumes 

 that strays are only half as successful at spawning as are "naturals" and a 

 fitness value of assumes that strays are unable to successfully reproduce. 



