from the viewer {as the figures in this paper 

 are shown); (2) whether broken circuli or 

 segments of circuli are present in the posterior 

 field, (3) whether circuli invade the posterior 

 field from their bases; (4) the occurrence of 

 radial striations or ridges; and (5) the presence 

 and type of reticulations. Figure 2 shows the 

 features of the posterior field. 



LIFE HISTORY FEATURES THAT INFLUENCE 

 SCALE CHARACTERS 



Pacific salmon usually spawn and deposit 

 their eggs in the gravel of a suitable stream 

 or lake in the late summer and fall. The eggs 

 develop, and the fry hatch in the gravel during 

 the winter and spring. Steelhead trout usually 

 spawn late in the winter or spring, and the 

 young hatch within a few weeks. The young fish 

 of both groups emerge from the gravel at 

 about the time the yolk-sac has been absorbed. 



Young of the pink salmon (O. gorbuscha ) and 

 chum salmon (O. keta ) migrate to the sea soon 

 after emerging from the gravel, usually before 

 the scales have started to grow. Young of the 

 other species usually remain and grow in 

 freshwater from 1 to 4 years before migration 

 to the sea although a large portion of the 



GRANULAR 

 RETICULATIONS 



CIRCULI COMPLETE 

 BELOW FOCUS 



NO RETICULATIONS 



CIRCULAR STRIATIONS 



Figure 2. — Features of the posterior field (clear area) 

 of value in species Identification — posterior sections 

 of a chum (upper) and a chlnook (lower) salmon scale — 

 are shown. 



Chinook salmon (O. tshawytscha ), especially 

 those from British Columbia southward to 

 California, may migrate seaward after only a 

 few months in fresh water. 



After the period of fresh-water growth, most 

 of the sockeye (O. nerka ), chinook, coho 

 (O. kisutch), and masu salmon and steelhead 

 trout migrate to the ocean in early spring just 

 as rapid scale growth begins, so that the scales 

 usually show a definite winter mark at the 

 margin of the fresh-water growth zone. As 

 mentioned previously, since growth is much 

 more rapid at sea, it is possible to determine 

 the exact boundary of the fresh-water growth 

 on most scales. 



Salmon and trout do not develop scales until 

 they are between 25- 50 mm. long ( 1 to 2 inches); 

 thus their scales have no record of the first 

 winter in the gravel. Those fish that migrate 

 to the sea immediately after leaving the gravel 

 show rapid growth on the scale directly from 

 the focus. 



After a period at sea that varies from a few 

 months to a maximum of 5, or occasionally 6 

 or 7 years, depending on the species, the 

 salmon return to the stream where they origi- 

 nated to spawn and die. Sometime during this 

 migration, the fish stop feeding and utilize 

 the protein and fat stored in the body. As the 

 migration progresses, the drain on the body 

 becomes greater, and the fish resorb portions 

 of the scales. By the time spawning is com- 

 pleted, only small central sections of the 

 scales are left on most individuals. Determina- 

 tion of total age or identification of species 

 from such scales is difficult or impossible. 



Unlike the Pacific salmon, steelhead trout 

 do not necessarily die after spawning. Instead 

 they may return to the sea where they recover 

 from spawning and continue to grow until they 

 again return to fresh water to spawn. This 

 species also resorbs scales at the time of 

 spawning, but generally to a lesser extentthan 

 do salmon. After spawning, the irregular scale 

 margins caused by the resorption are repaired 

 by new growth. These repaired areas or scars 

 are called spawning checks. The scales of 

 steelhead trout may show one or more spawn- 

 ing checks, which can assist in identification 

 of this species . 



Different species behave differently and are 

 found in coastal and offshore waters during 

 different parts of their life histories. These 

 differences in habit and habitat can influence 

 the age of the fish at the time of capture and 

 consequently the utility of age as an item for 

 identifying species. Maturing chum, sockeye, 

 and to a lesser extent pink salmon generally 

 do not take a lure or bait in coastal or fresh- 

 water areas and must be caught with various 

 types of nets. Commercially caught chum 

 salmon are 3 to 6 years old; 5- and 6-year 

 old fish are more common in Alaska and the 

 Western Pacific Ocean than from British 

 Columbia southward where the 3- and 4-year 



