16 



and first lowo«t on record, respectively; and that in 1990 just 78 wild 

 fish were estimated to have passed Lower Granite Dam, only 31% of the 

 number in the next lowest year (1987). 



Waples et al. (1991) evaluated the use of two time series of data for 

 applying the Dennis model to SnaJce River fall Chinook in an effort to 

 determine extinction likelihood, and concluded that a statistically 

 significant change in growth rate parameters of the population occurred 

 for runs that returned following construction and operation of the four 

 lower river dams (about 1980; the first year for which almost all 

 returning adults had to outmigrate through Lower Granite Dam as 

 juveniles). Because a time series used to estimate extinction 

 probabilities that spans a fundamental change in parameters affecting 

 the population can give misleading results, Waples et al. (1991) leaned 

 heavily on the 1980-1990 estimates of "natural" fall chinooVc crossing 

 Lower Granite Dam and concluded based ui?on application of the Dennis 

 model to this data set that the probability of extinction within 100 

 years was 10.8%. This probability of extinction (based upon recent 

 population trends) was less than the 95% probability of extinction level 

 suggested by Thompson (1991) as a minimum viable population threshold 

 for endangered status. However, other considerations and the higher 

 probability of extinction associated with using a longer time trend in a 

 second Dennis model led NHFS staff to conclude that a threatened listing 

 decision was in order. Waples et al. (1991) concluded their stock 

 status report with the following statement: 



In light of the above factors, and further conaidering that a) 

 drought conditions have likely adversely affected juvenile 

 survival in several recent years, reducing the prospects for 

 recovery in the near future as these year classes return as adults 

 and b) there is clear evidence that stray hatchery fish of non- 

 Snake River origin pose a serious threat to the genetic integrity 

 of the wild population, the BRT concluded that Snake River fall 

 Chinook salmon face a substantial risk of extinction if present 

 conditions continue . 



Following the Waples et al. (1991) paper and a proposed rule by NMFS to 



add Snake River fall chinook to the endangered species list with the 



status being defined as threatened (June 27, 1991; 56 FR 29547), various 

 reviewers to the proposed rule stated that fall chinook should be listed 



as endangered rather than threatened. On April 22, 1992, NHFS responded 



to this very pointed criticism in the final rule and specifically 

 stated : 



The threatened species designation in the proposed rule was based 

 on an assessment of the best available scientific and commercial 

 information , taking account of efforts to protect the species. In 

 making its final determination , NMSS considered the 1991 estimated 

 escapement of 318 wild adult fall chinook salmon above Lower 

 Granite Dam. This represents a considerable increase over the 

 1990 estimated escapement of 78 adults. Further, starting in 

 1991, all hatchery-produced fall chinook from the Snake and 

 Umatilla Rivers were tagged in order to separate adult hatchery 

 and wild fish at Snake River dams. Tagged hatchery fish will be 

 prevented from ascending further upstream, while wild fish will be 

 allowed CO proceed. This measure will be significant in reducing 

 any introgression of the Snake River gene pool with Columbia and 

 Snake River hatchery-produced fall chinook salmon. Furthermore, 

 at Lyons Ferry Fish Hatchery, the practice of taking wild fish for 

 brood stock has been stopped. Despite the need for caution in 

 using the moat recent years figure in determining a trend, this 

 increase approaching previous escapement levels typical of the 

 1980s may be attributable, at least in part, to the protective 

 measures already undertaken . Consequently, HMFS is issuing a 

 final determination to list the Snake River fall chinook salmon as 

 threatened under the ESA. 



A very notable change in the NMFS approach to Snake River fall chinook 

 and the listing status determination question is apparent in the two 

 1994 Federal Registers (emergency status change rule dated August 18, 

 1994, and the proposed permanent reclassification dated December 28, 

 1994). Rather than relying upon a reasoned, objective analysis of 



