25 



This indicatea chat the probabilities of the Snake River fall Chinook 



run having escapements in excess of 300 fish is considerably higher than 



was the case based on recent years; and, the level of jeopardy is 

 reduced over the recent year model runs. 



Assuming that reasonable and prudent alternatives are implemented to 

 benefit listed salmon under the final biological opinion for the 

 hydrosystem, which will be issued as a result of the lOFC v. NHFS 

 judgement, the probabilities of Snake River fall chinook escapements 

 exceeding 300 fish will increase over the levels modeled with the 

 original 1994-1998 biological opinion. 



Indeed, when the STFA used hydro management options as defined under the 

 Detailed Fishery Operating Plan (DFOP 1993) with 16 options under a 

 variety of assumptions concerning depensation, transport benefits, and 

 predator control effectiveness, the STFA estimated that the proportion 

 of yearly escapements at or above 300 for a 24 year period was always 

 1.00 (always exceeded the benchmark level of 70%) and the proportion of 

 yearly escapements at or above 300 for a 100 year period was also always 

 1.00 (always exceeded the benchmark level of 90%). 



It is uncertain exactly how the hydro system will be managed in coming 

 years, but it is likely that alternatives will be implemented that will 

 increase the probability that escapements will exceed 300 fish. Hence, 

 Snake River fall chinook are in less jeopardy now than was the case at 

 the time of listing (the model results associated with recent BY 80-88). 

 The STFA model results do not support chanaino the status of Snake River 

 fall Chinook from threatened to endangered . The status of Snake River 

 fall Chinook is projected to improve over conditions in place at the 

 time of listing because of altered and improved hydro system management. 



Spawner-Racruit Relationthip 



Two spawner-recruit relationships were developed for the Snake River 

 fall Chinook salmon stock. The first relationship was developed using 

 only natural adult escapements estimated to pass over Lower Granite Dam 

 and the second relationship was developed using all adults counted over 

 Lower Granite Dam. Escapement data used ia provided in Table 3 (column 

 1 for naturals and column 6 for the total escapements). Estimates used 

 to apportion escapements by age were taken from Roler (1994) for the 

 197S-1993 escapements and the 1983-93 average was used for the 1994 

 escapement. 



Total returns (recruits) were calculated in adult equivalents (A£Q) for 

 both catches and escapements. Returns in the escapement were calculated 

 back to the river mouth by dam conversion rates included from the CTC 

 Chinook model IDL file which agree favorably with those conversion rates 

 documented in NM7S (1994). Catches were calculated by exploitation rate 

 analysis (ER) provided in the Pacific Salmon Commission chinook model 

 (CTC 1994) for ocean and terminal catches. The Pacific Salmon 

 Commission chinook (PSC-C) model does not include in-river test fish 

 catches or some subsistence and ceremonial catches. Consequently, 30% 

 was added to in-river catches provided in the PSC-C model to account for 

 these catches. The PSC-C model exploitation rates are based upon coded 

 wire tag analysis, out-putting total ER, ocean ER, and terminal ER. 

 Total AEQ return is calculated from ESC/l-ER. Consequently, total 

 returns were calculated as escapement to the river mouth plus terminal 

 catches plus ocean catches, with both terminal and ocean catches 

 adjusted to AEQs. Simple Ricker spawner-recruit relationships were 

 fitted to the paired sets of spawners and total returns. 



The estimated average AEQ return for the 1975-1989 brood years was 2,949 

 fish, composed of an escapement to the river mouth of 1,573 fish, an 

 ocean AEQ catch mortality of 849 fish, and an in-river AEQ catch 

 mortality of 527 fish (Table 12). Parent year escapements averaged 485 

 natural spawners. Ocean mortality averaged 29% and in-river mortality 

 (from fishing and dams) averaged 56% of the total AEQ return and 

 averaged 78% of the return to the river mouth. Return per spawner 

 averaged 6.7, which is high for a population with high out-migrant 

 mortality (i.e., even with 91% to 96% downstream mortality, an average 



