EBEL. PARK, and JOHNSEN: EFFECTS OF TRANSPORTATION 



Adult returns (14 of 20) from those marked 

 and transported after 13 May indicated that 

 about 70% of the juveniles migrating seaward 

 after that date were summer chinook salmon. 

 All returns (11) from those marked after 19 

 May were summer chinook salmon — again 

 indicating that the latest juvenile outmigrants 

 are from summer chinook salmon populations. 



This, in part, explains why the benefit from 

 transport (2.8:1 ratio of transport/control fish) 

 was so much higher for summer chinook salmon 

 than for spring chinook salmon. After heavy 

 spilling at dams, from early May on, a higher 

 proportion of the juvenile population consisted 

 of summer chinook salmon. The obvious impli- 

 cation is that the control groups released from 

 this time on were largely wiped out by gas 

 bubble disease, caused by high concentrations 

 of nitrogen gas from the heavy spillway dis- 

 charges. 



Steelhead Trout 



Juvenile steelhead trout were transported 

 from 28 April to 1 June 1969, each group 

 being marked with a distinctive weekly brand; 

 90% of those that returned as adults in 1970 

 arrived at Ice Harbor between 24 September 

 and 14 October. There was no particular rela- 

 tion between time of seaward migration and 

 time of return. Adult returns from juveniles 

 marked between 28 April and 1 June were 

 equally distributed throughout the return 

 period, 24 September-14 October. 



We examined scales to determine whether 

 the adults were predominantly 1- or 2-year 

 freshwater smolts at the time of their down- 

 stream migration. All adults had lived 2 years 

 or more in fresh water. Only 19 scale samples, 

 however, had legible freshwater annuli. The 

 size of these fish was of interest. After spending 

 only 1 year in the ocean, they averaged 61 cm 

 and 2.6 kg. No significant difference was found 

 between size of control fish and transported 

 fish. 



Retention of Cold Brand and 

 Magnetic Tag 



We were particularly interested in deter- 

 mining the percentage of brand retention on 



adult fish that had been cold branded as 

 juveniles during the course of this study. Both 

 cold (Mighell, 1969) and hot (Groves and 

 Novotny, 1965) brands have been used success- 

 fully as short-term marks on chinook salmon 

 and steelhead trout; up to the time of this 

 study, however, no information was available 

 concerning the retention of the brand to adult- 

 hood by chinook salmon and steelhead trout. 



Clifford Long (National Marine Fisheries 

 Service, Pasco, Wash., pers. comm.) determined 

 that the brand was retained by 70% of the 

 jack coho salmon marked for his studies; the 

 Fish Commission of Oregon had similar results 

 with coho salmon they had branded (Groves 

 and Jones, 1969). Although we attempted to 

 duplicate the techniques used by the above 

 authors, the salmon and trout that we branded 

 did not retain brands as well as the retention 

 reported for coho salmon. Forty percent of 

 our brands were not detectable on the spring 

 and summer chinook salmon when they re- 

 turned as adults (Table 7). The brand was 

 legible (Figure 4) on 38% but only partially 

 legible on 22% . Of the steelhead trout brands, 

 64% were legible, 24% illegible, and 12% par- 

 tially legible. The size and physiological condi- 

 tion of the fish at the time of marking may 

 have affected brand retention. The chinook 

 salmon and steelhead trout we marked were 

 smolting. Size range of the chinook salmon 

 was 80-140 mm and of the steelhead trout, 

 160-250 mm. 



Average overall tag loss for all groups was 

 determined by comparing returns to Rapid 

 River Hatchery of: 1) adults with adipose fin 

 clips and wire nose tags with 2) adults with 

 adipose fin clips only. 



Approximately 27% of the juvenile chinook 



TABLE 7. — Quality of marks ("cold" brands) on adult 

 chinook salmon and steelhead trout that had been 

 branded as juveniles during their downstream migration. 



Species 



Chinook 

 Steelhead 



212 

 115 



80 

 74 



38 

 64 



46 

 13 



22 

 12 



86 

 28 



40 

 24 



559 



