15 



provisions of this Act would present an overwhelming snd 

 overriding risk to mAn. 



The term 'threatened species' meajis Any species which is likely to 

 become an endangered species within the foreseeable future 

 throughout all or a significant portion of its range. 



NMFS made an attempt to better define these terms relative to listing 

 decisions concerning salmon through a paper by Thompson (1991). Under 

 the recommendations ■•ction, Thompson (1991) states: 



Likewise, the various analytic approaches can provide useful 

 information with a minimum of time and data. As an example of how 

 such approaches can be used, the density-independent diffusion 

 model and estimation procedures described by Dennis et al . (in 

 press) will be considered below in some detail. 



In discusBing the Dennis model, Thompson goes on to say: 



Finally, implementation of this or any other model requires 

 choosing p* and c* values. Actually two sets of threshold values 

 are required in the context of ESA, since the Act defines two 



levels of jeopardy (endangered and threatened) , As noted in the 

 Introduction, it is unfortunate that the ESA does not define 

 endangerment with much precision. In the absence of further 

 guidance , perhaps the best decision for "endangered" p* and c 

 values is to accept the conventional wisdom chat sets p* = 0.95 

 and f •• 100. In other words, at the 'endangered' level, HVP is 

 the population size that gives a 95\ chance of extinction over the 

 next 100 years. 



While the ESA is decidedly vague regarding the definition of 

 endangerment, it does give some indication of how 'threatened' p" 

 and t" values should relate Co their 'endangered' counterparts . 

 Since a threatened species is defined as one which is 'likely Co 

 become endangered within the foreseeable future,' one need only 

 interpret the terms 'likely' and 'foreseeable future' to relate 

 'threatened' HVP to the 'endangered' MVP. A reasonable 

 interpretation of a 'likely' event would be one which has at least 

 a 50% chance of occurring . Quantifying 'foreseeable future' is 

 not so straightforward, but perhaps something like 10 years would 

 be satisfactory . In other words, the 'threatened' HVP is the 

 population size that gives a 50\ chance of reaching the 

 'endangered' MVP within 10 years. 



This provided a fraine of reference for the KHTS initial decisions 

 concerning the status of various salmon stocks including Snake River 

 fall Chinook at the time this stock was added as a threatened species to 

 the endangered species list. 



THREATENED VERSOS ENDANGERED STATUS 



The basic question is whether status of Snake River fall chinook has 

 changed since Waples et al. (1991) evaluated stock statue and NMFS 

 provisionally decided in 1991 to list this stock as a threatened 

 species, a decision that NMFS subsequently reaffirmed with a final 

 listing decision in 1992. 



Waples et al. (1991) evaluated a number of factors' in considering the 

 level of risk faced by Snake River fall chinook salmon in 1991 and 

 concluded that: 



the current population occupies a fraction of its former range, 

 the remaining (and historically, the moat productive) habitat 

 having been inundated by reservoirs or blocked by dams. 



Waples et al. (1991) concluded that adult returns of Snake River fall 

 chinook declined by three to four orders of magnitude from pristine 

 levels. Waples et al. (1991) specifically recognized that the estimated 

 number of wild spawners in 1987, 1989, and 1990 were the second, fourth. 



