155 



(1) Are adequate proportions of the smolts likely to be found in shallow water? 



I conclude that about 30 % of the smolts inhabit the shaJ!v>w water, based on the 

 reports of Smith (1973) who reported about 30 ° b of juvenile cliinook were in the upper 

 three feet of the water at Lower Monumental Dam on the Snake Rj'ver. This was 

 confirmod by Dawley (1986) who found a jiniilar distribution of chiiiook juveniles in the 

 forebay of the Dalles Dam on the Columbia River. 



(2) Are times to mortality short enougli to kill smolt3 at prevailing gas le\els in 

 shallow water? 



I concluded that times to 5 "■'o mortality are sufficiently short to be oporative, as 

 judged from Table 1. which lists the a%erace times to 5 % mortalit>- for juveniJ'J rainbow 

 trout in shallow water (30 cm) at \arious hvperbaric gas (dP) pressures. 



Table 1. Hours to five percent mortality for rainbow trout 

 Oncorhynchus mykiss at various hyperbaric gas pressures. 



250 200 150 100 



133 126 119 113 

 4.0 5.7 J7.1 215 



95 % Umit= 0.3 0.8 0.5 4.9 x 

 Range= 1.0-3.0 1.8-5.8 4.1-7.2 13.5.39.9 29.3-502 

 Ntest»= 16 10 14 14 9 



The exposure times needed to kill 5 "-b of *e fish generally falls well within tlie 

 time period of a single night. That is. when nominal zas levels were 139 %. 133 ""u. and 

 126 %. 5 Vo of the fish were killed in 1.6. 4.0. and ?.7 hours respectively. When gas 

 levels were 1 19 °'o, the mean time to 5 "^'o mortalit>' v\as slightly over one day (27 hour>>. 

 AppKinK a 5 % mortality rate to 30 "o of the population (which is found in shallow water) 

 produces aii estimated average kill of (5° o mortilit>- X 30 <?'o of the fish X 24 27 of a da> ) 

 = 1.3 % mortality of the total smolts per day at gas levels of about 1 19 %. If the gas level 



