FISHERY BULLETIN: VOL. 86. NO. 2 



Table 5. — Release Information and mean travel speeds in kilometers per day and body length (BL) 

 per second for CWT and fluorescent-pigment marked age .0 coho salmon recovered in the ocean 

 within 10 days of release. CR ^ Columbia River: OAF = Oregon Aqua Foods, Inc., (OAF Yaquina 

 is 3.7 km from ocean; OAF Coos Is 14 km from the ocean), Anad. - Anadromous Inc. (7.4 km from 

 the ocean). 



Effects of Ocean Currents 



The tendency for juvenile coho salmon to move 

 to the south early in the summer and to the north 

 later in the summer (Figs. 4—8) may be related to 

 advection of water and the size, orientation, and 

 swimming speeds of fish. Generally, surface cur- 

 rents are to the south off Oregon and Washington 

 in the early summer owing to prevailing north- 

 westerly winds (Hickey 1979; Huyer 1983). 

 Southward flow averaging 17-34 km d"^ (Huyer 

 et al. 1975, 1979) has been measured near the 

 surface. May and June are periods of peak outflow 

 of the Columbia River, so fish entering the ocean 

 at this time, especially in the Columbia River 

 plume, may be displaced to the south by advection 

 of surface waters. Southward flow is at a maxi- 

 mum in the coastal jet which is strongest (—22 km 

 d~^) during the spring about 15-20 km from 

 shore (Kundu and Allen 1976; Huyer et al. 1979). 

 Since currents can be equivalent to 1.7 BL s"^ for 

 a 15 cm smolt, advection alone could explain the 

 southward movement of most marked Columbia 

 River fish during May and June but not the rapid 

 northward movement of fish during this period 

 (see Figures 4-7). 



Coastal Oregon fish were often found to the 

 north in May and June, but these fish were usu- 

 ally substantially larger and generally released 

 much earlier in the spring than Columbia River 



fish, and were presumably better able to swim 

 against the current. Later in the summer when 

 Columbia River hatchery fish had grown larger, 

 movement was also predominately northward. In 

 August and September southward velocities of 

 surface coastal currents are diminished and the 

 mean may be near zero (Huyer et al. 1975). 

 Northward movements during the summer off 

 Oregon and Washington generally cannot be ex- 

 plained by passive drift and in most years must 

 entail active, oriented swimming. 



The northern El Nino of 1982-83, which had 

 severe effects on the growth and survival of adult 

 and jack coho salmon (Pearcy et al. 1985; Johnson 

 1984; Pearcy and Schooner 1987; Fisher and 

 Pearcy in press), also appeared to affect the distri- 

 bution of juvenile coho salmon. During Septem- 

 ber of 1983 nearly all the seine-captured juvenile 

 coho were taken along our northernmost transect, 

 off Cape Flattery, WA (Fig. 2). In other years 

 juvenile coho salmon during late summer were 

 common and more equally distributed from the 

 Columbia River northward. In the summer of 

 1983 juvenile coho salmon may have moved far- 

 ther north, or more likely those to the south may 

 have experienced higher mortality, as a result of 

 northerly currents (Huyer and Smith 1985), 

 warm temperatures and low productivity (Pearcy 

 et al. 1985; Chung 1985) that prevailed off Ore- 

 gon. 



188 



