Fisher and Pearcy: Distribution, migration, and growth of Oncorhynchus tshawytscha 



277 



salmon at the time they entered the Columbia River 

 estuary was usually under 100 mm FL, whereas that 

 of yearling chinook salmon was about 130-150 mm 

 FL (Dawley et al., 1985a). Between January and July 

 1981-83 about eight times as many subyearling fish 

 as yearling fish were caught at rkm 75 (purse and 

 beach seines combined, Dawley et al., 1985a). Dur- 

 ing the same period an average of 2.3% of subyearling 

 fish and 2.5% of yearling fish caught at rkm 75 were 

 CWT'd (calculated from data in Dawley et al., 1985, 

 a and b). Large numbers of subyearling chinook 

 salmon, the mean lengths of which ranged from 91 

 mm in May to 135 mm in September, were caught in 

 shallow (<4 m water depth) marine waters outside 

 of the river mouth in some years (Dawley et al. 1 ). 



Most naturally reared chinook salmon from coastal 

 Oregon river systems also enter the ocean as 

 subyearling smolts (Nicholas and Hankin, 1988). 

 Peak abundance of subyearling chinook salmon in 

 Oregon estuaries generally occurs from late June 

 through August (Reimers, 1973; Nicholas and 

 Hankin, 1988). Although peak abundance in estuar- 

 ies is earlier, juvenile chinook salmon are often 

 caught in estuaries in the late fall (Myers and Horton, 

 1982; Nicholas and Hankin, 1988). By September, 

 subyearling chinook salmon smolts caught in beach 

 seines in the lower estuaries were generally from 100 

 to 130 mm mean FL (Nicholas and Hankin, 1988). 



Ocean migrations of stocks originating in north- 

 ern California and in Oregon south of Cape Blanco 

 are limited in extent, and few maturing fish of these 

 stocks are caught outside of the California and Or- 

 egon ocean or freshwater fisheries (Nicholas and 

 Hankin, 1988; Garrison 5 ). However, some northern 

 coastal Oregon and Columbia River stocks (both 

 spring and fall runs) undertake very extensive mi- 

 grations and are caught in large numbers in the ocean 

 fisheries of Alaska and northern British Columbia 

 (Nicholas and Hankin, 1988; Garrison 5 ; Hansen and 

 Johnson 6 ; Howell et al. 7 ; Vreeland 8 ). 



5 Garrison, R. L. 1986. Stock assessment of anadromous salmo- 

 nids. Oregon Dep. Fish Wildl., Annual Prog. Rep., Portland, OR 

 97207, 47 p. 



6 Hansen, H. L., and R. L. Johnson. 1987. An evaluation of fish- 

 ery contribution from fall chinook salmon reared in Oregon 

 hatcheries on the Columbia River, coded-wire-tag recovery pro- 

 gram. Oregon Dep. Fish Wildl., Annual Prog. Rep., Portland, 

 OR 97207, 47 p. 



7 Howell, P.. K. Jones, D. Scarnecchia, L. LaVoy, W. Kendra, and 

 D. Ortmann. 1985. Stock assessment of Columbia River anadro- 

 mous salmonids. Vol. 1: chinook, coho, chum and sockeye salmon 

 stock summaries. Final Rep., U.S. DOE, Bonneville Power 

 Admin., Div. Fish Wildl., Portland, OR 97208. 



8 Vreeland, R. R. 1986. Evaluation of the contribution of chinook 

 salmon reared at Columbia River hatcheries to the Pacific 

 salmon fisheries. Annual Rep., U.S. DOE, Bonneville Power 

 Admin., Div. Fish Wildl., Portland, OR 97208. 



127^ 



125^ 



123° 121° 



49 l 



47^ 



45^ 



43^ 



WASHINGTON 



Columbia R. 



ASTOfllA 



41 



39^ 



i-yPuget Sound 



Klamath ft. 



Sacramento ft. / 

 San Joaquin ft. 



Figure 1 



Sampling areas (A, B, C) where juvenile chinook salmon, 

 Oncorhynchus tshawytscha, were collected in purse seines, 

 1981-85. Sampling sites occupied in 1983 are shown (dots) 

 along with the 40 and 120 m depth contours (dashed lines). 

 Basins which are major sources of chinook salmon in this 

 region are indicated by arrows. Latitudinal extent of sam- 

 pling varied in the different months and years (see Fig. 5). 



Methods 



Chinook salmon were collected with a fine-mesh 

 purse seine between May and September, 1981-85, 

 along a series of east-west transects off Oregon and 



