EBEL, PARK, and JOHNSEN: EFFECTS OF TRANSPORTATION 



release, 97 from the transported release — a 

 ratio of 2.1:1 of transport/control. This return 

 ratio is higher than that shown for the returns 

 of summer chinook salmon transported and 

 released at John Day. Although the juvenile 

 fish migrated downstream in different years 

 (1968 for Chinook salmon; 1969 for steelhead 

 trout), environmental conditions were similar. 

 During both years, heavy spilling prevailed 

 at the time of release and concentrations of 

 dissolved nitrogen gas were very high. 



If gas bubble disease caused by supersatura- 

 tion of nitrogen was the main factor deter- 

 mining survival of these groups, susceptibility 

 of the salmon and trout to lethal levels of 

 nitrogen gas in the river must have been 

 similar or the ratios of returning adults would 

 not have been similar. This, of course, is 

 merely a hypothesis; several other factors 

 which cause change in survival could also 

 have been responsible for the similarity of 

 the ratios. 



This return ratio also indicates that the 

 ability of steelhead trout to return or "home" 

 to Ice Harbor Dam was not appreciably af- 

 fected by transporting the seaward migrants 

 around a portion of their downstream route. 



Recovery of Marked Chinook 



Salmon in Commercial and 



Sport Fisheries 



Returns to the commercial and sport fisheries 

 in the lower Columbia River (Table 6) are 

 based on the spring fishery and indicate a 

 definite benefit from transportation. The return 

 ratio of transported fish (John Day-Bonneville 

 releases combined) to control fish was 1.4:1. 

 The marked increase in the transport/control 

 ratio for summer-run adults taken at Ice Harbor 

 Dam is not reflected in the commercial fishery 

 because of the closure on summer-run chinook 

 salmon. 



It was not possible to distinguish between 

 returns to the fishery from releases at Bonne- 

 ville and John Day because of the loss of the 

 identifying brands. Brands which would have 

 enabled identification by release site were 

 obliterated by gill-net abrasion. Transported 

 and control groups could be distinguished by 



TABLE 6. — A comparison between transported and 

 noniransportcd groups of chinook salmon based on 

 numbers of transported and nontransported juvenile 

 fish that were recaptured as adults by commercial and 

 sport fisheries in the lower Columbia River, 23 February 

 through 11 August 1970 and 1971. 



magnetic tags, but only two codes were used 

 — one for the controls and one for the trans- 

 ported fish. However, if the percentage of 

 adult returns obtained at Ice Harbor — where 

 brands of fish returning from releases at 

 Bonneville and John Day were visible — is 

 applied to the total transport returns obtained 

 in the commercial fishery, the ratio of transport/ 

 control becomes 1.7:1 for fish transported to 

 Bonneville Dam. 



Returns of Adults to 

 Spawning Grounds 



Spring and Summer Chinook Salmon 



Spawning ground surveys (Figure 3) and 

 examination of tagged adult fish at Rapid 

 River Hatchery near Riggins, Idaho, provided 

 further information concerning the ratios of 

 transi)ort/control spring and summer chinook 

 salmon at their "home" destination. During 

 the study, 65 tagged fish were recovered from 

 Rapid River Hatchery; an additional 29 were 

 from sport fishermen and spawning ground 

 surveys. Of these fish, 52 were from the trans- 

 ported groups and 42 from the control group. 

 By adjusting for the ratio of John Day to 

 Bonneville returns, we estimated that 36 of 

 the 52 transported fish were from the group 

 released at Bonneville Dam. The ratio, then, 

 of transi)ort/control fish for the group released 

 at Bonneville becomes 1.7:1 when computed 

 on the basis of the number of juveniles re- 

 leased per group. This is nearly identical to 



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