prints of projected plastic impressions of scales.' 

 Explanations and descriptions of the various fea- 

 tures accompany the plates. 



The original plates were assembled on 15- by 

 20-inch mounting sheets. Magnification of the 

 individual scales and scale sections was adjusted 

 for reduction onto the usual 8- by lOi/2-iiich 

 page; in this reduction, however, the clarity of 

 the scale characters varies somewhat ; therefore, 

 I suggest that the reader keep a small magnify- 

 ing glass (2 to 4X) handy for examination of 

 specific portions of the plates as needed. 



Examples of negative and positive prints of 

 scales, a comparison of scales and their pla.-tic 

 impressions, the appearance of scale features 

 under various magnifications, a glossary of terms 

 used in scale studies, and the method of making 

 •the photogi-aphs are presented in the appendix. 



The following order of topics has been chosen 

 as the most useful for study of scales from sock- 

 eye salmon : 



1. Gross features of sockeye salmon scales 



(plates 1 and 2). 



2. Circuli, winter zones, and ages in the 

 fresh-water growth zone (plates 3, 4, and 

 5). 



3. Transition zone between fresh- water and 

 ocean growth ( plate 6 ) . 



4. Appearance, number, and spacing of cir- 

 culi, winter zones, and ocean ages in the 

 ocean growth zone (plates 7-11 ) . 



5. Age group combinations in sockeye salmon 

 (plates 12-16). 



6. Anomalies which make some scales un- 

 usable for age and racial studies (plates 

 17, 18, and 19). 



7. Use of the atlas. 



8. Appendix. 



FEATURES OF SCALES FROM 

 SOCKEYE SALMON (Plate 1) 



Under magnification, a sockeye salmon scale 

 shows two distinct areas: (1) The anterior or 

 sculptured field, which was embedded in the scale 

 pocket and (2) the posterior or unsculptured 

 field, which protruded from the scale pocket and 



overlapped the adjacent posterior scale pockets. 

 The examples sho\\ai in plate 1 and plate 2 illus- 

 trate these and other gross features described 

 below. Scales of Pacific salmon are cycloid scales. 



ANTERIOR FIELD 



The upper surface of the anterior field is 

 sculptured with ridges (circuli) and gi'ooves 

 (interspaces). See Koo and Finn (1964) for 

 photographs of magnified cross sections of sal- 

 mon scales. Under magnification the circuli and 

 interspaces appear as alternating light and dark 

 concentric "rings" which result from differences 

 in transmission of light through the grooves and 

 ridges of the translucent scale material.- The 

 contrast between circuli and interspaces varies 

 from high (heavily marked circuli) to low 

 (lightly marked circuli).^ Circuli are formed on 

 the edge of the scale as it grows (Neave, 1936; 

 Welander, 1940; Wallin, 1957). When the scales 

 are growing rapidly (in late spring and sum- 

 mer) , the circuli are deposited relatively far 

 apart and have a broad and heavy appearance 

 and texture (as if ch-awn with a blunt pencil or 

 stub-tipped pen). The periods of retarded 

 growth (in the fall, winter, and early spring) 

 show on the scale as bands of circuli lying closer 

 together than the circuli of the summer growth 

 zone. These bands have been called annual 

 marks, annual rings, winter zones, winter 

 checks, winter growi^h zones, resting zones, or 

 annuli.^ Where zone dimensions are needed, most 

 salmon scale workers measure to the last circulus 

 of this band of closely spaced circuli. 



The circuli laid down while the fish is in fresh 

 water are of finer texture than those deposited 

 later while the fish is in the ocean (as if drawn 

 with a sharp pencil or fine-tipped pen). This cen- 



1 See Mosher (1950) for a description of the scale projector. See 

 Clutter and Whitesel (1956) or Koo (1962a) for a description of tlie 

 method of making plastic impressions of the scales. 



2 The circuli appear as the light rings in the negative prints ana 

 the interspaces as the dark rings (see appendix plate 3). 



3 The differences in contrast between circuli and interspaces are 

 not as evident in the photographs as they are when the scales or 

 scale impressions are examined directly. For reproduction 1 have ad- 

 justed the contrast between the light and dark tones to near maximum 

 wherever possible. 



■> Annul! of sockeye salmon scales, unlike those of most other fish, 

 are bands of closeb spaced circuli formed during the winter and 

 early spring. The usual definition of an annulus as a line of discon- 

 tinuity between successive growth zones does not describe most annuli 

 in the ocean growth zones of the sockeye salmon scale. Such lines of 

 discontinuity often occur between the fresh-water and ocean growth 

 zones whether or not an annulus is present and often occur on the 

 scale at various places not related to the presence of the bands of 

 closely spaced circuli which form each winter. 



PHOTOGRAPHIC ATLAS OF SOCKEYE SALMON SCALES 



245 



