Abstract. — Little is known of 

 the early ocean life of juvenile Chi- 

 nook salmon, Oncorynchus tshaw- 

 ytscha. During the summers of 1981 

 through 1985 we collected juvenile 

 chinook salmon with fine-mesh 

 purse seines in shelf waters off the 

 Oregon and Washington coasts. 

 Most coded- wire tagged (CWT) fish 

 caught in the ocean were yearlings 

 from Columbia River basin hatch- 

 eries. Catch per unit of effort of 

 CWT yearling fish was much higher 

 in the May-June period than in the 

 August-September period, prob- 

 ably, for the most part, because of 

 the migration of these fish out of 

 the sampling area by late summer. 

 CWT subyearling fish were more 

 abundant in late summer than in 

 spring and early summer. A few fish 

 from the Columbia River Upriver 

 Bright stock of fall chinook salmon 

 were recovered many months after 

 release near where they entered the 

 ocean, indicating that northward mi- 

 gration of some smolts from this 

 highly migratory stock may be de- 

 layed for several months following 

 release, or that some individuals of 

 the stock undertake less extensive 

 migrations than others. Subyearling 

 smolts were rare in our catches, de- 

 spite the larger spawning popula- 

 tions producing these smolts than 

 those producing the yearling smolts 

 in this area. Subyearling fish may 

 have been mainly distributed in 

 shallow water inshore of our sam- 

 pling. Our largest catches of small 

 chinook salmon (<130 mm FL) were 

 taken in the low salinity, high-tem- 

 perature waters of the Columbia 

 River plume. CWT fished were usu- 

 ally recovered north of where they 

 entered the ocean, except in May 

 1982 when southward currents 

 were strong. Average net rate of mi- 

 gration of yearling smolts between 

 the head of the Columbia River es- 

 tuary and ocean capture was 4.1 

 kmd 1 . Average growth rate of 

 CWT yearling fish downstream of 

 river km 75 in the Columbia River 

 was 1.05 mmd" 1 . Average instan- 

 taneous rate of growth in weight of 

 yearling CWT Columbia River fish 

 between hatchery release and cap- 

 ture in the ocean was 0.92% body 

 wtd -1 . 



Manuscript accepted 29 August 1994. 

 Fishery Bulletin 93:274-289 (1995). 



Distribution, migration, and growth 

 of juvenile chinook salmon, 

 Oncorhynchus tshawytscha, 

 off Oregon and Washington 



Joseph R Fisher 

 William G. Pearcy 



Oceanography Administration Bldg. 104 

 College of Oceanic and Atmospheric Sciences 

 Oregon State University. Corvallis, OR 97331-5503 



The Columbia River once produced 

 the largest runs of chinook salmon 

 (Oncorhynchus tshawytscha) in the 

 world (Van Hyning, 1973). Today, 

 runs are only a fraction of the size 

 they were in the late 19th and early 

 20th century (Chapman, 1986), and 

 a large fraction of the present popu- 

 lation is produced in hatcheries. 

 Although the runs of Columbia 

 River chinook salmon are affected 

 by many factors (e.g. dams, fresh- 

 water habitat depredation, ocean 

 fisheries, etc.), environmental con- 

 ditions during early ocean life also 

 may be important determinants of 

 year-class success for these fish. 



Little is known of the early ocean 

 distribution, migration, and growth 

 of chinook salmon during their first 

 year in the ocean prior to becoming 

 vulnerable to ocean fisheries. Hartt 

 and Dell (1986) collected juvenile 

 salmon with purse seines over a 

 wide area of the Gulf of Alaska and 

 the Bering Sea in the late 1950's 

 through the early 1970's. Although 

 relatively few juvenile chinook 

 salmon were caught during their 

 sampling (358 fish in 505 sets be- 

 tween 1964 and 1968; their Appen- 

 dix Table Al), subsequent recover- 

 ies of juvenile fish tagged at sea 

 provided information on early ocean 

 migrations of these fish. Four juve- 

 nile fish tagged in the northern Gulf 

 of Alaska in July and August of the 

 fish's first summer in the ocean 

 were recovered in later years in the 



spring in the Columbia River, indi- 

 cating that some Columbia River 

 spring chinook salmon migrate rap- 

 idly to the north into the Gulf of 

 Alaska during the first three or four 

 months of ocean life (Hartt and Dell, 

 1986). 



Miller et al. (1983) caught juve- 

 nile chinook salmon with purse 

 seines in the ocean off southern 

 Washington and northern Oregon 

 during three periods in 1980: late 

 May through early June; July; and 

 late August through early Septem- 

 ber. They sampled in water where 

 the bottom depth was >30 m near 

 the mouth of the Columbia River, a 

 major source of chinook salmon 

 smolts. Marked Columbia River 

 spring chinook salmon (yearling 

 smolts) were caught only during 

 their spring cruise, and only in 

 gillnet sets that opened to the south, 

 suggesting that this stock group 

 migrates rapidly to the north soon 

 after entering the ocean (Miller et 

 al., 1983). Very few fish <130 mm 

 FL were found over water greater 

 than 30 m bottom depth, in contrast 

 to the great numbers of small fish 

 caught in shallow marine waters 

 near the surf zone by Dawley et al. 1 



1 Dawley, E. M., C. W. Sims, R. D. Ledger- 

 wood, D. R. Miller, and J. G. Williams. 

 1981. A study to define the migrational 

 characteristics of chinook and coho salmon 

 in the Columbia River estuary and associ- 

 ated marine waters. Coast. Zone and Es- 

 tuarine Studies Div., Northwest Fish. 

 Sci. Cent., NMFS, Seattle WA 98112. 



274 



