29 



that straying of hatchery fish above Lower Granite Dam was merely 

 coincidental with the advent of coded wire tag technology. 

 Consequently, it seems likely that at least some level of introgression 

 of the gene pool called "naturals" has occurred due to straying of 

 hatchery fish. Thus the gene pool of progeny of fish that spawn in the 

 wild today is likely different than it was a few years ago. 



A similar dilution model was developed for the Lyons Ferry Hatchery 

 brood stock (Figure 15). Results indicate that the current brood stock 

 is likely more similar to the prior "natural" stock than is the current 

 population of fall Chinook spawning in the wild and this is because of 

 the efforts at the hatchery to protect the genetic integrity of the 

 brood stock. 



Although there is a clear potential for introgression of the Snake River 

 fall Chinook gene pxsol by Columbia River hatchery strays, the question 

 of fitness of these strays remains somewhat open. Waples et al. (1991) 

 provided genetic data showing the relationship of Snake River fall 

 Chinook to other Columbia River Chinook populations as well as showing 

 how allelic frequencies of Snake River fall chinook were potentially 

 converging with Upper Columbia River fall chinook populations. 



Since the initial listing decision, fall chinook salmon spawning in the 

 Snake River have been genetically sampled along with outmigrating 

 juveniles and Lyons Ferry hatchery fish. Although results from much of 

 this research have not been published and made generally available, the 

 researchers involved with these studies have verbally told Alaska 

 Department of Fish and Game staff that: 



• Samples of fall chinook adults returning to the Snake River, 

 including strays, have an increased genetic affinity to the 

 Columbia River cluster of populations. 



• Samples of juveniles collected from the Snake River cluster 

 with the historic Snake River fall chinook group rather than 

 with any other group. 



• The genetic distances, albeit small, between Snake River and 

 Columbia River fall chinook, observed by NMFS in the 1970s, 

 generally persist through 1994. 



• Rare genotypes endemic to the Snake River fall chinook 

 population persist in the 1994 juvenile collection. 



• Stray chinook from the Columbia River apparently have not 

 shifted the frequencies of the Snake River outmigrants, nor 

 have they swamped rare endemic genotypes. 



• Snake River fall chinook rare genotypes have not been lost due 

 to bottlenecking. 



• The available genetic data indicates that the Columbia River 

 strays have not contributed substantially, at least yet, to the 

 Snake River gene pool. 



• Although the Snake River fall chinook ESU is facing challenges 

 from straying and bottlenecking, the ESU remains basically 

 intact through 1994. 



• Lyons Ferry Hatchery is the reserve for genotypes for the ESU 

 and Lyons Ferry Hatchery fish should be included in the ESU. 



The dilution modeling results and comments from geneticists studying 

 potential introgression of the Snake River fall chinook salmon ESU 

 indicate that it would be prudent to add the Lyons Ferry Hatchery brood 

 stock into the Snake River fall chinook salmon ESU. The following 

 factors also support the inclusion of the Lyons Ferry Hatchery brood 

 stock. 



26-104 - 96 - 2 



