36 



Fishery Bulletin 102(1) 



cious, sexually developed males) among the fish was prob- 

 ably a consequence of their very large size at ocean entry 

 and their high rates of growth in the ocean. 



Freshwater origins of juvenile salmonids 



Allozyme data were collected from samples of 247 chinook 

 salmon, 88 coho salmon, and 58 steelhead. Genetic mixed 

 stock analyses indicated that chinook salmon in June were 

 predominately (54%, SD=0.18) from rivers and hatcheries 

 along the mid Oregon coast, an area immediately north of 

 Cape Blanco (Table 5, Fig. 5). In August, chinook salmon 

 were largely from rivers that enter the sea south of Cape 

 Blanco. Fish from the Sacramento and San Joaquin rivers 

 in northern California were estimated to comprise 90% 

 (SD=0.07) of the chinook salmon sampled in August north 

 of Cape Blanco. The largest concentration of chinook 

 salmon we sampled was south of Cape Blanco in August, 

 and these fish were mostly from rivers in southern Oregon 

 (539(, SD=0.10) and the Sacramento and San Joaquin 

 rivers (20%, SD=0.05). Chinook salmon from the Colum- 

 bia River Basin were also present, but were estimated 



to comprise only 18% (SD=0.15) of the June sample and 

 8% (SD=0.05) of the August sample north of Cape Blanco. 

 Recoveries of hatchery chinook salmon bearing coded-wire 

 tags (CWT) provided direct evidence of stock origins for 

 ten fish, all taken in trawls north of Cape Blanco (Table 

 5). These data reveal that hatchery fish released from 

 the Umpqua River on the central Oregon coast (;;=6), 

 Columbia River Basin («=3) and Sacramento River (« = 1) 

 contributed to our sample of chinook salmon. The propor- 

 tion of CWT fish from the Umpqua River in our August 

 catch north of Cape Blanco (8%) indicated that the con- 

 tribution of mid Oregon coastal fish was underestimated 

 in the genetic analysis likely because of the small size of 

 the mixture sample. 



Genetic estimates of coho salmon indicated that most 

 fish originated from coastal Oregon rivers north of Cape 

 Blanco (479S , SD=0.10) and from the Columbia River (13%, 

 SD=0.08 ) (Table 5 ). However, a substantial proportion (40 r /i , 

 SD=0.09) of coho salmon were from coastal rivers south of 

 Cape Blanco, a region that includes spawning populations 

 in the Rogue and Klamath rivers. Eight coho salmon in 

 our sample contained CWTs and showed that fish from 



