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Fishery Bulletin 93(2). 1995 



rkm 75 and capture in the ocean were 0.75 mm-d" 1 

 (rc=152) and 1.05 mm-d -1 (n=31), respectively, for all 

 years combined. The higher estimated growth rates 

 for fish downstream of rkm 75 suggest that growth 

 rates offish in the Columbia River Estuary and ocean 

 were higher than growth rates in the areas upstream 

 in the Columbia River. Growth rates between rkm 

 75 and ocean capture were 0.98 (n=5), 0.98 (n=21), 

 and 1.41 mm-d" 1 (n=5) in 1981, 1982, and 1983, re- 

 spectively. Average instantaneous rate of growth in 

 weight of age-1.0 C WT Columbia River juvenile chinook 

 salmon between hatchery release and ocean capture 

 was 0.92% body wt-d -1 (« = 152), for all years combined. 



Discussion 



Age-1.0 chinook salmon smolts from the Columbia 

 River basin migrate rapidly to the north after enter- 

 ing the ocean in the spring. Evidence for this rapid 

 northward migration is found in the sharp decrease 

 between early and late summer in CPUE of CWT 



age-1.0 fish in the area off Oregon and Washington 

 (Table 5); in the much higher CPUE of age-1.0 fish 

 in the area north of the Columbia River than south 

 of the Columbia River in June (Fig. 2); in the low 

 CPUE of age-1.0 fish in late summer (Fig. 2); and in 

 the predominantly northward migrations of CWT 

 Columbia River fish (Fig. 5). These results are con- 

 sistent with those of Miller et al. (1983), who found 

 CWT age-1.0 fish only in their late spring sampling 

 in 1980 off southern Washington and northern Or- 

 egon, and who caught CWT age-1.0 fish only in purse- 

 seine sets that were open to the south (sets that catch 

 northward swimming fish). Our results are also con- 

 sistent with those of Hartt and Dell (1986) who 

 caught juvenile Columbia River spring chinook sal- 

 mon in the northern Gulf of Alaska in August of their 

 first year in the ocean. Only in May 1982 were many 

 CWT age-1.0 Columbia River fish found to the south 

 of the Columbia River (Fig. 5). This was a period of 

 strong northerly winds and southward flowing sur- 

 face currents which may have transported the juve- 

 nile salmon to the south by advection (Pearcy and 

 Fisher, 1988). 



Unlike age-1.0 chinook salmon, age-1.0 coho 

 salmon were fairly abundant in late summer off the 

 Columbia River mouth and off Washington (Pearcy 

 and Fisher, 1988). The Columbia River is the major 

 source for both of these species in the study area, 

 and yearlings of both enter the ocean at about the 

 same time (April through June). The continued pres- 

 ence in late summer of age-1.0 coho salmon off the 

 Columbia River and Washington coast suggests that 

 they are less migratory than yearling Columbia River 

 chinook salmon during their first summer in the 

 ocean. As maturing fish, these two species of salmon 

 generally also have different ocean distributions. A 

 major part of the ocean catch of several stocks of 

 Columbia River spring chinook salmon occurs far to 

 the north in British Columbia and Alaska ocean fish- 

 eries (e.g. Willamette R. and Klickitat R. stocks); con- 

 versely, Columbia River and coastal Oregon coho 

 salmon stocks are mainly caught in Washington, 

 Oregon, and California ocean fisheries (Garrison 5 ; 

 Howell et al. 7 ). This divergence in the ocean distri- 

 butions of these two species is already apparent in 

 the first few months of their ocean life. 



On the basis of estimated growth rates of CWT 

 fish, we concluded that both age-1.0 coho and chinook 

 salmon appear to grow at fairly similar rates during 

 the first few months they are in the ocean. Estimated 

 mean growth rates of CWT age-1.0 Columbia River 

 chinook salmon between release and capture in the 

 ocean (0.75 mm-d -1 ) and between rkm 75 and cap- 

 ture in the ocean (1.05 mm-d -1 ) were similar to the 

 estimated mean growth rate of juvenile coho salmon 



