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



275 



Hence, they concluded that offshore movement of 

 chinook salmon is size dependent, beginning when 

 the fish are about 130 mm FL (Miller et al., 1983). 



Healey (1980, 1991) studied juvenile chinook 

 salmon in Georgia Strait, British Columbia. He found 

 that "stream-type" chinook salmon (those spending 

 a year in streams before entering the ocean) were 

 only abundant in marine sampling from about late 

 April to late May, suggesting that these fish migrated 

 out of the protected waters of Georgia Strait soon 

 after leaving fresh water. Conversely, "ocean-type" 

 fish (those entering salt water as small subyearling 

 fish ) were abundant in the protected marine waters of 

 Georgia Strait throughout the summer and early fall. 



In this study we describe the abundance, distribu- 

 tion, migration, and growth of juvenile chinook 

 salmon collected by purse seine during the spring 

 and summer of 1981-85 in coastal marine waters from 

 northern Washington to southern Oregon. This study 

 extends the temporal and spatial scope of available 

 information on the early ocean life of juvenile chinook 

 salmon off Oregon and Washington. The following para- 

 graphs include a short review of life histories, spatial 

 and temporal patterns of hatchery releases, and sea- 

 ward migrations of different stocks of chinook salmon 

 smolts in the area from northern Washington to north- 

 ern California to aid the reader in the interpretation of 

 the distribution and movement of juvenile chinook 

 salmon in the ocean as presented in this paper. 



The majority of stocks of chinook salmon found 

 along the coast of North America from northern 

 Washington to northern California return to rivers 

 to spawn in the fall (i.e. are fall-run fish), and their 

 offspring migrate to the ocean as subyearling smolts 

 (ocean- type) in the summer or fall of the same year 

 during which they emerge from the gravel (Nicholas 

 and Hankin, 1988; Healey, 1991). Although stocks 

 that enter the ocean as yearling smolts ( stream-type ) 

 are also found in this region, mainly in large river 

 systems ( e.g. the Columbia River ), they are not as abun- 

 dant as the ocean-type stocks (Healey, 1983, 1991; 

 Nicholas and Hankin, 1988; Table 1, this paper). Most 

 stream-type fish begin their upstream spawning mi- 

 gration in the spring (i.e. are spring-run fish), and the 

 downstream migration of their offspring to the ocean 

 as smolts begins earlier than that of the ocean-type 

 fish (Healey, 1982; Dawley et al., 1985, a and b). 



Total releases of yearling and subyearling fall and 

 spring chinook salmon from coastal Washington, 

 Columbia River, and coastal Oregon hatcheries av- 

 eraged 138 million fish per year in the two-year pe- 



riod 1982-83 (Table l 2 ). Of these releases, about 75% 

 were subyearling fall chinook salmon, 14% were 

 subyearling spring chinook salmon, and 11% were 

 yearling spring chinook salmon (Table 1). (A much 

 smaller number of summer, winter, and late fall 

 chinook salmon, not included in Table 1, were also 

 released in these two years). 



Fish from the Columbia River accounted for over 

 89% of all hatchery releases of chinook salmon in 

 this area; Columbia River subyearling fall, subyear- 

 ling spring, and yearling spring chinook salmon rep- 

 resented 66%, 12%, and 11% of the total, respectively. 

 Subyearling fall chinook salmon from coastal Wash- 

 ington and coastal Oregon hatcheries represented 6% 

 and 2% of the total release, respectively. Subyearling 

 spring chinook salmon from coastal Oregon hatcher- 

 ies represented 2% of the total release. 



Most subyearling fall chinook salmon from the 

 Columbia River and coastal Washington hatcheries 

 were released from April through June at a small 

 size (about 4 or 5 g body wt; Table 1). A smaller pro- 

 portion of subyearling fall chinook salmon from these 

 two areas was also released later in the year at a 

 much larger size (Table 1). In contrast, most 

 subyearling fall and subyearling spring chinook 

 salmon from coastal Oregon hatcheries were released 

 in late summer or fall at a large size (averaging 

 roughly 30-60 g; Table 1 ). Releases of yearling Co- 

 lumbia River spring chinook salmon were concen- 

 trated in the April^June period, whereas releases of 

 subyearling Columbia River spring chinook salmon 

 were spread throughout the year. 



Some of the fish released from hatcheries were 

 marked with coded- wire tags (CWT) from which the 

 release history of the fish could be obtained. In the 

 two years examined, an average of 2.9% of the 

 subyearling, and 6.5 7c of the yearling fish released 

 from January through June in the Columbia River 

 drainage were marked with CWT's. 



Releases of chinook salmon smolts from Califor- 

 nia hatcheries averaged about 30 million fish per year 

 in 1982 and 1983, most of which were fall chinook 

 salmon. 3 Of the California releases about 25 million 

 were small subyearling fish in the spring and about 

 5 million were large subyearling fish in the fall. 



Extensive sampling of juvenile salmon in the lower 

 Columbia River (rkm 75) between 1977 and 1983 

 determined that yearling chinook salmon smolts en- 

 tered the Columbia River estuary (at rkm 75) mainly 

 from April through June and that peak migration 



2 This table was compiled from data received in 1994 from the 

 salmonid release data files of the Regional Mark Information 

 System of the Pacific States Marine Fisheries Commission, 45 

 SE 82nd Drive, Suite 100, Gladstone, OR 97027-2522. 



3 Calculated from data supplied in 1994 bv Frank Fisher, Calif. 

 Dep. Fish, and Game (CDFGl, 2440 North Main St., Red Bluff. 

 CA; Gary Ramsden, CDFG, Trinity River Hatchery, Lewiston, 

 CA; and Kim Rushton, Iron Gate Hatchery, 8638 Lakeview Rd. 

 Hornbrook, CA. 



