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Fishery Bulletin 93(2). 1995 



lumbia River (CO) in May 1985 (Fig. 2, bottom). For 

 each month and area the effort (number of purse- 

 seine sets) and total CPUE are also shown. The 

 length-frequency distributions of CWT age-1.0 Co- 

 lumbia River fish are shown in black, and lengths of 

 other CWT fish are indicated by letters (Fig. 2). 



In the May and June samples, most CWT age-1.0 

 fish from the Columbia River were between 130 mm 

 FL and 250 mm FL. As discussed earlier, from the 

 percentages of CWT fish in the catches, most un- 

 marked fish in this size range were probably also 

 age-1.0 hatchery fish from the Columbia River. On 

 the basis of CWT's and scale characteristics, we con- 

 cluded that larger fish (about 220-400 mm FL) in 

 May and June were a mixture of age-1.0 and age-0.1 

 fish. CPUE of fish in May was greatest in Area B, 

 which straddles the mouth of the Columbia River, 

 and was about half as great in areas to the south (C) 

 and to the north (A). Relative to May, CPUE in June 

 decreased in Area C, remained about the same in Area 

 B, and increased in Area A. CPUE in June was much 

 higher in the two northern areas than in Area C. 



Age-1.0 Columbia River fish were much rarer in 

 all areas in the July-September period than in the 

 May-June period, based both on the catches of CWT 

 fish and the length-frequency distributions of un- 

 marked fish. Generally, CPUE of fish between 150 

 mm FL and 330 mm FL was low in July and August in 

 all areas. In September only a few age-1.0 and age-0.1 

 fish were caught in Area A. Only one CWT age-1.0 fish 

 (340 mm FL) was caught in Area C in September. 



The most abundant fish in July and August were 

 less than 150 mm FL (Fig. 2). Catches of these small 

 fish were highest off northern California (CA), the 

 Columbia River (B), and the Washington coast (A). 

 The few CWT fish caught in July and August in this 

 size range were age-0.0 fish from the Columbia River 



( Fig. 2 ). The catches in the ocean in July and August 

 of these small fish coincided with the time of peak 

 abundance of subyearling chinook salmon in Oregon 

 estuaries (Nicholas and Hankin, 1988) and with the 

 later half of the peak migration of subyearling 

 chinook salmon in the Columbia River estuary 

 (Dawley et al. 4 ) and was well after the time when 

 most yearling chinook salmon enter the ocean (in 

 May, Dawley et al. 4 ). Therefore, it is most likely that 

 the unmarked fish <150 mm FL caught in the ocean 

 in July and August were age-0.0 fish. 



Catches of chinook salmon in September in Areas 

 B and C occurred mainly in 1983 and 1984. In Sep- 

 tember 1984, 32 moderately large (range 160—260 

 mm FL) fish were caught off Oregon (Area C). These 

 were mainly age-0.0 fish released in August from the 

 Anadromous Inc. release facility on Coos Bay (this 

 conclusion was based on associated CWT fish and 

 their percentage of the catch). 



During September 1983 we caught 207 unmarked 

 juvenile chinook salmon in areas B and C off Oregon. 

 Fish caught in area B were smaller (mean FL=185, 

 ra=35) than those caught to the south in area C (mean 

 FL=227 mm, rc=172; Fig. 2). Estimated mean FL at 

 time of ocean entry backcalculated from scales was 

 138 mm and 173 mm for fish caught in areas B and 

 C, respectively. Growth while in the ocean averaged 

 48.5 mm for fish caught in area B and 52.2 mm for 

 fish caught to the south in area C. Dividing by a growth 

 rate of 1.5 mm/d, we estimated time since ocean entry 

 to be just over one month for both these groups. 



The estimated date of ocean entry of these fish 

 (sometime in mid or late August) indicates that these 

 were subyearling rather than yearling chinook 

 salmon, since both naturally and hatchery produced 

 yearling fish generally enter the ocean in the spring 

 or early summer (see the introduction to this study). 



