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b. Fall chinook salmon 



With respecc to the proposed goal, 288 adult wild fall chinook 

 salmon per year for 4-5 years would represent about 1,150-1,440 

 adult fish per generation arriving at Lower Granite Dam. After 

 accounting for pre-spawning mortality and other factors (uneven 

 sex ratio and high variance in reproductive success) that 

 generally cause the effective size of natural populations to be 

 substantially lower than the census number, the goal still can be 

 expected to result in an N. per generation of several hundred. 

 This is true even at the low point of the trajectory described in 

 Table 1 (five year average of 225 adults) . This should be large 

 enough to minimize the short-term risks to the population from 

 inbreeding and erosion of genetic variability. 



c. Spring/summer chinook salmon 



Assuming each redd corresponds to approximately 2.5 adult fish, 

 an average of 2,052 spring/ summer chinook saimon redds per year 

 corresponds to a population abundance during the base period of 

 about 20,000 - 25,000 wild adults per generation (2,052 

 redds/year x 2.5 fish/redd x 4-5 years/generation) . Even 

 allowing for 1) a reduction in effective population size below 

 the census number and 2) the projection that abundance would 

 decrease to 9,303 redds per 5 years or about 1,860 redds/year by 

 1997 (Table 1) , it appears that the target population size is 

 large enough that no significant problems from inbreeding would 

 be expected if the population behaved as a single, randomly 

 mating unit. 



There continues to be some concern that local populations of 

 spring/summer chinook salmon could fall below desired levels. 

 NMFS anticipates that it may be necessary to establish individual 

 subbasin escapement goals for spring/summer chinook salmon. 

 However, not all of the life cycle models are designed to project 

 escapements to individual subbasins. We expect that additional 

 refinements in our evaluation criteria and reductions in 

 mortality will be needed to provide for long-term recovery. As a 

 result, for purposes of the combined-effects analysis, NMFS will 

 defer consideration of individual subbasin escapement goals 

 pending further analysis. 



Demographic considerations 



The other problem associated with low population size is the risk 

 of extinction. To date, NMFS' ESA evaluations have used a simple 

 drift-diffusion model (the "Dennis model", Dennis et. al 1991), 

 in conjunction with other information, to evaluate the degree of 

 risk faced by a population. We can apply this model to assess 

 the risk to populations that would result if the proposed 



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