157 



The offspring of these sockeye--and a male that returned this year-will be held in two 

 hatcheries as part of a captive breeding program. The resulting progeny will not be released 

 into the river to migrate, but will be kept in captivity for their entire lifespan to increase 

 their chances of surviving and producing offspring. Theoretically, at a future date when the 

 population reaches some, as of yet, undetermined numerical and biological strength, the 

 resulting offspring from the captive breeding stock will be re-introduced to their natural 

 habitat. 



Limiting this endeavor to the progeny of a few sockeye has enormous genetic risk. 

 When a population is subject to inbreeding because of severely restricted numbers over a 

 protracted period, as Snake River sockeye have for the past 50 years or more, a great deal of 

 genetic diversity is lost. (Geneticists call this a genetic bottleneck, see Figure. 1.) To limit 

 broodstock for recovering the Snake River sockeye to four plus fish is to further restrict that 

 diversity. Small populations possess little genetic variability and are therefore at great risk of 

 extinction because of inbreeding and/or the inability to deal with environmental changes over 

 time. Many potential genetic problems face small populations. Those problems include 

 increased juvenile mortality due to inbreeding, loss of genetic diversity through founder 

 effect and genetic drift, the physical expression of deleterious recessives, interaction of 

 demographic and genetic effects, and inadvertent selection for domestication (Ralls and 

 Ballou 1986). Although not a genetic risk factor, a single catastrophic event~a power 

 outage, for instance—could also wipe out an entire captive population. 



The genetic diversity that enables a salmon species to persist over time is found 

 within the whole range of that species. Trying to keep the genetics of salmon static in a 

 rapidly changing environment, as hfMFS' captive br^ding program is attempting, works 

 against natural evolutionary processes. Only by providing a species with its full genetic 

 diversity might it then be able to adapt and survive under changing conditions. For a 

 population that has experienced severe genetic bottleneck, the added diversity from inter- 

 breeding with other populations (hybridization) can provide that advantage. 



Hybridization Is a Natural Occurrence 



For a time, the U.S. Fish and Wildlife Service had an official policy against hybrids. 

 The agency abandoned the policy in 1990 (FWS. CW. 0440), after finding "new biological 

 information [that] casts doubt on the validity of the absolute pronouncements relied upon 

 [earlier], since in some cases introgression between taxa is not only a naturally occurring 

 phenomenon but may also be a necessary recovery measure to avoid the loss of a seriously 

 depleted listed taxon." 



In a March 1991 Science article about the Endangered Species Act, the founder of the 

 biological species concept. Dr. Ernst Mayr, and his associate, molecular biologist Dr. 

 Stephen J. O'Brien, emphasized that "living organisms are constantly evolving and that over 

 time hybridization may result in new, unique species." Mayr and O'Brien pointed out that, in 

 the case of endangered or threatened species, a ban on hybridization between sub-species or 



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