fish, but often the circuH are so uniformly spaced 

 that no area of widest spacing can be identified. 

 Plate 9 shows example.s of these variations in 

 spacing of circuli within the first ocean growth 

 zone, as follows: 



Figure 1. A scale from an Asian sockeye sal- 

 mon with the widest spaced circuli 

 (arrow) immediately preceding 

 the winter ocean growth. 



Figure 2. A scale from a Bristol Bay sockeye 

 salmon with the widest spaced cir- 

 culi (arrow) formed immediately 

 after migration to the ocean. 



Figure 3. A scale from a Cook Inlet sock- 

 eye salmon with a summer growth 

 zone of widely and uniformly 

 spaced circuli. 



Figure 4. A scale from a Skeena River sock- 

 eye salmon with a summer growth 

 zone of unifoiTnly spaced circuli. 



Figure 5. A scale from a Rivers Inlet sockeye 

 salmon with a summer growth 

 zone of evenly and closely spaced 

 circuli. 



Figure 6. A scale from a Columbia River 

 sockeye salmon with a summer 

 growth, zone of widely and uni- 

 formly spaced circuli. 



WINTER ZONES IN OCEAN GROWTH (Plate 10) 



Winter zones in the ocean gro'W'th result from 

 slower scale growth in the fall, winter, and early 

 spring, during which time the circuli are foraied 

 closer together than during the faster gi-owth 

 in the late spring and summer. Zones of winter 

 growth in the ocean, like those in the fresh-water 

 portion of the scale, also vary in appearance; 

 they may be classified into four general groups 

 on the basis of appearance (winter zones in the 

 illustrations are nimibered as follows) : 



1. Clear-cut zones made up of a number of 

 closely spaced circuli. 



2. Zones made up of circuli less closely spaced 

 or more numerous than those of group 1. 



3. Diffuse zones the boundaries of which 

 cannot easily be identified. Whereas the 

 circuli are closer together tlian the adja- 

 cent summer growth zones, either the dif- 



ference between the spacing of circuli is 

 so slight or the narrowing of the circuli 

 into the winter zone is so gradual that it is 

 difficult to be sure of the exact boundaries 

 of tlie zone. 

 4. Winter zones characteristic of the first 

 ocean zone of most sockeye salmon from 

 Rivers and Smith Inlets, British Columbia, 

 where the circuli are often only slightly 

 closer together than the closely spaced cir- 

 culi of the summer growth. 



The winters of ocean life of the fish not only 

 must be accurately identified for age determina- 

 tion, but their location and boundaries must be 

 measured exactly in many racial and other stud- 

 ies; therefore, scales with diffuse winter zones 

 (gi-oup 3) may be difficult or impossible to use 

 in some of these studies. 



AGE GROUPS BY NUMBER OF WINTERS IN THE 

 OCEAN (Plate 11) 



Sections of sockeye salmon scales showing 

 ocean gi-owth zones illustrate the range of ocean 

 ages found in this species.'" Arrows indicate the 

 winter growth zones. 



.0 — only a few months in the ocean, no 



winter growth zone 

 .1 — one winter in the ocean 

 .2 — two winters in the ocean 

 .3 — three winters in the ocean 

 .4 — four winters in the ocean 

 .5 — five winters in the ocean 



SCALES WITH DIFFERENT COMBINA- 

 TIONS OF FRESH-WATER AND 

 OCEAN AGE 



All the combinations of fresh-water and ocean 

 age that I liave found in sockeye salmon are il- 

 lustrated in plates 12 to 16. Age designations 

 of adult salmon follow the recommendations of 

 Koo (1962b). Two methods may be used — the 

 European method or the Gilbert and Rich (1927) 

 method. The Gilbert and Rich method is used on 

 the following plates; in- the text, age designa- 



10 Age designation of salmon in reference to marine life only 

 follows the recommendations of Koo (1962b) : a dot followed by the 

 number of winters the fish spent in the ocean. 



PHOTOGRAPHIC ATLAS OF SOCKEYE SALMON SCALES 



259 



