FISHERY BULLETIN: VOL. 86, NO. 2 



groups of juvenile coho, classified as age 0.0 or 1.0 

 from scale analysis, are shown in Figure 2, for 

 1981-84 in three regions: (A) Cape Flattery, WA 

 to Grays Harbor, WA (called Washington), (B) 

 Willapa Bay, WA to Nehalem Bay, OR (Columbia 

 River region), and (C) Cape Lookout, OR to Coos 

 Bay, OR (Oregon) (Fig. 1). In May of 1981, 1982, 

 and 1983, average catch per set of yearling (age 

 1.0) coho generally decreased from the southern 

 to the northern regions. Catches v^ere highest off 

 Oregon (Area C) or the Columbia River (Area B) 

 and lowest off Washington (Area A) in May of 

 1982 and 1983. This trend was reversed later in 

 the summer. In June of 1981, 1983, and 1984, 

 lowest catches were found in the Oregon region. 

 By August or September 1981-84, highest 

 catches consistently occurred off the Columbia 

 River or Washington and few yearling fish were 

 caught off Oregon. These shifts in abundance sug- 

 gest a northerly movement of age 1.0 smolts dur- 



ing the summer. Highest catch rates occurred in 

 May and June of 1981 and 1982 when an average 

 of over 10 juvenile coho salmon were caught in 

 most sets. 



Subyearling or age 0.0 coho salmon released 

 from private facilities at Yaquina and Coos Bays 

 provide more direct evidence on movements. Sub- 

 yearling coho salmon clearly demonstrated 

 northward dispersal. They were most common in 

 our catches of July 1981 and September 1982, 

 1983, and 1984 (Fig. 2). They were apparently 

 more numerous than age 1.0 coho salmon in the 

 Oregon region during June-August 1981 and 

 September 1982, and in the Oregon and Columbia 

 River regions in September 1983. The catches and 

 proportions of age 0.0 coho salmon increased off 

 Oregon during the summer because they were 

 released from hatcheries later in the summer 

 than yearling coho salmon. They were found in 

 the most northern region sampled late in the 



1981 



JUNE 



JULY 



....Mljlito^ 



i^i,i^»i 



AUGUST 



B 



C 



11*11(^1 



30 



10 



20 



30 



40 



FORK LENGTH (cm) 



Figure 2. — Catch per purse seine set of age 1.0 (open) and age 0.0 (shaded) juvenile coho by 10 mm length groups during different 

 months, 1981-84, for three regions of the Oregon-Washington coast: (A) Cape Flattery to Grays Harbor, WA, (B) Willapa Bay, WA 

 to Nehalem Beach, OR, (C) Cape Lookout to California. 



178 



