FISHERY BULLETIN: VOL. 86. NO. 2 



transport from Oregon Aqua-Foods, Inc. (OAF) 

 hatchery to their ocean release facilities at 

 Yaquina Bay or Coos Bay, OR. 



In the laboratory ashore, species identifications 

 were confirmed and individuals remeasured and 

 reexamined for both fluorescent marks (under ul- 

 traviolet light 1981-82) and missing adipose fins 

 or other marks (1979-85). Coded-wire tags from 

 the heads of salmonids with missing adipose fins 

 were decoded by personnel from the Oregon De- 

 partment of Fish and Wildlife, Clackamas Labo- 

 ratory. 



Juvenile or age .0 (first year in the ocean) coho 

 salmon were distinguished from adult or age .1 

 (second year in the ocean) coho salmon by exami- 

 nation of size-frequency histograms and scales. 

 The division between age .0 and .1 coho pro- 

 gressed from approximately 300 to 420 mm FL 

 from May to September, in most years. Most coho 

 salmon migrated to the ocean a little over one 

 year after hatching (age 1.0), but OAF released 

 large numbers of subyearling (age 0.0) smolts 

 into Yaquina Bay and Coos Bay. These two age 

 groups of smolts were distinguished by the radial 

 distance to the 21st circulus on scales removed 

 from the preferred area (Clutter and Whitesel 

 1956) of the fish. The accuracy of this method for 

 distinguishing known age 0.0 and 1.0 fish was 

 approximately 85-90%. In the years 1981-85, 

 scales from 52% of the 4,222 juvenile coho sam- 

 pled were analyzed. The estimated numbers of 

 age 0.0 and 1.0 fish represented in different 

 geographic areas and cruises were then extrapo- 

 lated from their proportions in each 10 mm length 

 interval. 



Distances traveled and movement rates were 

 estimated from actual distances between sites of 

 release and entry into the ocean, and from 

 straight-line distances between ocean entry and 

 recapture locations for CWT or fluorescent 

 marked juvenile coho salmon that were recovered 

 in the ocean within 10 days of release. These dis- 

 tances and swimming speeds are minimal esti- 

 mates. 



In addition to purse seining, fine-meshed 

 monofilament gill nets were used off the Oregon 

 coast (ca. lat. 45°00'N, long. 124°21'W) during 24 

 and 25 July 1985, from the training vessel Oshoro 

 Maru , to determine depth and direction of swim- 

 ming of juvenile salmonids. Surface and subsur- 

 face nets were used. The surface gill nets were 

 2,050 m long, and fished from depths of 0-6 m 

 with 11 mesh sizes ranging from 29 to 121 mm 

 (stretch). The subsurface nets were 500 m long 



and consisted of four mesh sizes ranging from 29 

 to 42 mm; they were suspended below large (300- 

 400 mm) mesh to fish at depths of 5-12 m. Four 

 sets were made in an east-west direction with 

 soak-times of about 4-9 hours. As the gill nets 

 were hauled, the direction that each juvenile 

 salmonid was heading when caught, and its depth 

 in the net (upper, middle, or lower section) were 

 noted. Each juvenile salmonid was given a con- 

 secutive number and frozen for later identifica- 

 tion. Comparisons of catch rates in the surface 

 and subsurface nets were based on equal lengths 

 of the four mesh sizes of the subsurface net, stan- 

 dardized to 10 hours of fishing time. 



Information on the location of landings of 

 marked juvenile coho by commercial and sports 

 fishermen was provided by the Pacific Marine 

 Fisheries Commission (PMFC), (PMFC 1980, 

 1981, 1984a, b, c, 1985a, b), from lists of non- 

 standard recoveries (Johnson PMFC unpubl. 

 data), and from state agencies. The actual num- 

 bers of tagged fish, and the total numbers of 

 tagged fish estimated from the proportions of the 

 catch sampled are reported. 



To determine if juvenile coho salmon were sex- 

 ually precocious "jacks", we examined testes from 

 542 juvenile males caught in July 1981 and 1984, 

 in August 1981, and in September 1982, 1983, 

 and 1984. All developed and some undeveloped 

 testes (ribbonlike, with no thickening), as deter- 

 mined by visual inspection, were weighed (123) 

 and gonadal-somatic indices (GSI = testes wt./ 

 body wt. X 100) were determined. 



RESULTS AND DISCUSSION 



Swimming Direction 



Of the 106 juvenile coho salmon captured dur- 

 ing June in paired, half-round purse seine sets, 

 all but two were in the sets open to the south 

 (Table 2). This suggests that juvenile coho salmon 



Table 2. — Catches of coho salmon In semicircular 

 purse seine sets open to the south (S) and north (N) off 

 Oregon, June 1979. 



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