FISHERY BULLETIN: VOL, 71, NO. 2 



O : Control 



• = Transport I test) 



FIGURE 3.— Location of tagged 

 adult Chinook salmon returns 

 from spawning ground surveys 

 and returns of tags from sport 

 fishermen in the Snake River 

 drainage. 



the ratio at Ice Harbor Dam for the Bonneville 

 release, indicating no straying or loss of 

 homing between Ice Harbor Dam and the 

 spawning grounds. 



The Chinook salmon spawning grounds of 

 the Okanogan and Methow Rivers and the 

 hatcheries on the Columbia River above and 

 below the mouth of the Snake River were 

 checked for returning tagged adults, but no 

 tagged fish were found. Thus, if straying to 

 these areas did occur, it was too small to 

 detect. 



Steelhead Trout 



Information on the return of adult steelhead 

 trout to their spawning ground is based solely 

 on recoveries of dart tags by sport fishermen. 

 To date (January 1972) only nine tags have 

 been recovered — two from the control group 

 and seven from the transported group. 



Timing of Seaward Migration of 



Juvenile Fish in Relation to 



Adult Returns 



Spring and Summer Chinook Salmon 



During marking of juveniles in 1968, a 



distinctive brand was used each week for the 

 transport and control groups. These identifying 

 brands provided a means of comparing the 

 timing of the downstream migration of the 

 juvenile fish with the timing of the upstream 

 (spawning) migration of the adult fish. Only 

 a small number (57) of adult returns could 

 be used for this comparison because the brand 

 on the adult fish had to be absolutely legible 

 to determine the time of downstream migration. 

 Returns from the control group could not be 

 used because poor environmental conditions 

 caused by supersaturation of dissolved nitrogen 

 gas apparently wiped out whole groups of 

 juvenile fish that were released during the 

 highest nitrogen concentration. For example, 

 over 37,000 fish were marked for the control 

 group and released between 5 May and 27 May; 

 only 1 adult fish was recovered from those 

 marked during that period. 



Adult returns of juveniles marked and trans- 

 ported between 12 April and 13 May indicate 

 that the juvenile population at that time is 

 mixed, with juvenile summer and spring Chi- 

 nook salmon evenly dispersed. Of 37 adult 

 returns from groups marked and transported 

 during this period, 20 were spring chinook 

 and 17 were summer chinook salmon. 



558 



