Type C. Diffuse transition is shown in figure 

 7. The transition between the fresh-water and 

 ocean [growth is so broken up by irregular cir- 

 culi tliat the exact boundaries of .the fresh-water 

 and plus growth (if any) are difficult to deter- 

 mine. 



OCEAN GROWTH 



The following plates show details of the ocean 

 growth zone, including tlie variations in : 



1. appearance of zones based on type of cir- 

 culi (plate 7). 



2. number of circuli (plate 8). 



3. spacing of circuli within the zones (plate 

 9). 



4. appearance of the winter zones (plate 10) . 



5. ocean ages (plate 11). 



APPEARANCE OF OCEAN GROWTH ZONES BASED 

 ON TYPE OF CIRCULI (Plate 7) 



The relative numbers of complete and inter- 

 rupted circuli affect the appearance of the dif- 

 ferent ocean zones and the ease and accuracy 

 with which measurements and counts of circuli 

 and winters of life can be made. See plate 2 for 

 examples of various types of circuli. Three broad 

 categories of ocean growth zones, based on the 

 circuli, are illustrated in plate 7. Each category 

 is illustrated by two photographs. 



Figure A shows the major portion of a scale 

 magnified about 20 X; figure B, which is the 

 central portion of the same scale magnified about 

 40 X, shows the circuli of the first ocean zone in 

 greater detail. The categories of ocean-growth 

 zones are described as follows : 



Category 1. A scale with mostly complete 

 circuli in the ocean-growth zones. 



Category 2. A scale with complete and irreg- 

 ular circuli in the ocean-growtli 

 zones (an "average" scale). 



Category 3. A scale with nearly every circu- 

 lus broken or otherwise inter- 

 rupted in the ocean-growth 

 zones. 



NUMBER OF OCEAN CIRCULI (Plate 8) 



The mean number of circuli in the first ocean 

 growth zone of scales from adult fish differ by 



geographical areas (table 1). The largest mean 

 numbers are on scales of sockeye salmon from 

 Rivers Inlet, British Columbia. Mean numbers 

 of circuli tend to be progi'essively lower on scales 

 of North American fish taken southward to the 

 Columbia River and northwestward to Bristol 

 Bay, Alaska. Scales from Asian fish have greater 

 mean numbers of circuli than the Bristol Bay 

 sockeye. This difference in mean numbers of cir- 

 culi holds true in all ocean zones but is most 

 pronounced in the first ocean zone. 



The scales in plate 8 were selected to show the 

 numerical differences in the number of circuli 

 in the first ocean zone (number of circuli be- 

 tween each pair of pointers) among sockeye sal- 

 mon from different geogi-aphical areas, as 

 follows : 



Figure 1. 

 Figure 2. 

 Figure 3. 



Figure 4. 

 Figure 5. 

 Figure 6. 



Asia, 25 circuli. 

 Bristol Bay, 22 circuli. 

 Ketchikan, Alaska (as representa- 

 tive of the area from Cook Inlet 

 to the Nass River, British Colum- 

 bia), 27 circuli. 



The Skeena River, British Colum- 

 bia, 29 circuli. 



Rivers Inlet, British Columbia, 32 

 circuli. 



The Columbia River, Oregon- 

 Washington, 26 circuli. 



SPACING OF OCEAN CIRCULI (Plate 9) 



Spacing of circuli within the ocean growth 

 zones may also vary bet\\'een scales from fish 

 collected in different geographical areas. In gen- 

 eral, scales with relatively large numbers of cir- 

 culi in the first ocean zone tend to have more 

 uniformly spaced circuli than those with fewer 

 circuli. On scales from Bristol Bay fish, the 

 widest spaced circuli are usually deposited near 

 the closely spaced fresh-water portion. On scales 

 from Asian fish, the widest spaced circuli are 

 often deposited just before the closely spaced 

 winter ocean circuli. On scales from fish taken 

 east and southeastward of Bristol Bay, the posi- 

 tion of the widest spaced circuli of the ocean 

 zones is less consistent. They may occur in the 

 .same position as in the Bristol Bay or the Asian 



PHOTOGRAPHIC ATLAS OF SOCKEYE SALMON SCALES 



255 



