FISHERY BULLETIN: VOL. 71, NO. 2 



FIGURE 4. — Spring chinook salmon with legible brand (arrow) captured at Ice Harbor Dam, spring 1970. 



salmon we tagged lost their tags between the 

 time they were released as juveniles and re- 

 turned as adults. The weighted average initial 

 tag loss of all groups measured after release 

 of juveniles in the river was 9.2% . This was 

 computed by checking recaptured juveniles 

 with brands and clips at The Dalles Dam and 

 by checking samples of fish released below 

 Bonneville Dam. Obviously an additional 18% 

 tag loss occurred sometime after the 9.2% 

 figure was established. This is much higher 

 than the loss (0.31%) determined by Bergman 

 et al. (1968). There are several possible explana- 

 tions for this high loss: 1) The population 

 we marked had a much wider size range 

 than the hatchery stock Bergman et al. used, 

 and this could have resulted in poor placement 

 of the tag in those fish that were either too 

 large or small for the tagging machine; 2) our 

 fish taggers were inexperienced in operation 

 of the machine; or 3) the Snake River has a 

 high incidence of pathogens which could cause 

 infection of the tag wound, resulting in rejec- 

 tion of the tag at a later date. 



A combination of the above factors probably 

 accounts for the high tag loss in our initial 

 experiments. We believe that continued train- 

 ing and experience of the tagging personnel 

 will result in a major reduction of tag loss 



560 



in the future. For example, initial tag loss in 

 1969 was reduced to 5% and in 1970, to less 

 than 1% . Although the loss was high in 1968, 

 it could be compensated for mathematically. 

 The basic information we needed from the 

 data was not affected. 



DISCUSSION 



All comparisons between the returns of 

 transported and control groups of spring chi- 

 nook salmon indicate that survival was defi- 

 nitely increased by transporting juvenile fish 

 to a release site downstream from Bonneville 

 Dam. The ratios varied from 1.7:1 in the 

 commercial fishery to 1.8:1 at Ice Harbor 

 Dam. Comparison between the control and 

 transported groups of summer chinook salmon 

 can be made only at Ice Harbor Dam. No 

 returns were obtainable in the sport and com- 

 mercial fishery because direct fisheries on these 

 fish have been restricted in recent years due 

 to decline in the size of run; only nine returns 

 were obtained on the spawning grounds. The 

 return ratio (2.8:1) at Ice Harbor Dam, how- 

 ever, clearly indicates a definite increase in 

 survival of transported summer chinook salmon. 



These ratios also provide information on 

 the effect of transportation on homing and 



I 



