The scales on this plate are arranged to show 

 increasingly greater degi'ees of scale resorption, 

 from A to H. 



Scales A and B. These scales show slight re- 

 sorption. Age determination is 

 possible with these scales. 



Scales C and D. These scales show considerable 

 resorption. Age detenninations 

 are subject to error. 



Scale E. This scale shows a gi-eater 



amount of resorption than 

 scales C and D, age determi- 

 nation is subject to considera- 

 ble doubt. 



Scales F and G. Only the fresh-water gro\\i;h 

 and a portion of the first year's 

 ocean gi'owth of these scales 

 remain. DeteiTnination of total 

 age is not possible. 



Scale H. This scale shows considerable 



resorption and a regenerated 

 center ; it is useless for age or 

 racial studies. 



OTHER SCALES NOT SUITED FOR AGE OR RACIAL 

 STUDIES (Plate 19) 



Scales can be unusable for a number of rea- 

 sons other than regeneration or resorption, as 

 sho\vn by the following examples : 



Scale A. Scales may be distorted with atypical 

 sculpturing. These scales often adjoin 

 regenerated scales. 



Scale B. Scales of adult and young fish may 

 have a twisted center or other dis- 

 torted area. If the gro^\i;h pattern is 

 not too badly distorted, the correct age 

 may be determined from the scale. 



Scale C. Scales may have scars (arrow). Here 

 again, if the damage is not too serious, 

 the correct age may be determined. 

 Scars are more common in the ocean 

 growth zones than in the fresh-water 

 zone — perhaps because the scales of 

 small fish are more easily lost than dis- 

 placed in the scale pocket. 



Scale D. Scales from the lateral line have a 

 trough or tubelike structure that forms 

 part of the lateral line organs. Scales 



near the lateral line inay also be dis- 

 torted to a varying degi'ee, but some 

 may be usable. 



Scale E. Scales of atypical size and shape oc- 

 cur near the bases of the fins and the 

 operculum ; they should not be used for 

 age or racial studies as they usually 

 have fewer circuli than preferred 

 scales. 



USE OF ATLAS 



Now that we have examined the features of 

 sockeye salmon scales in detail, we are ready to 

 use the atlas for specific purposes. This section is 

 divided into two parts: (1) The use of the atlas 

 in age studies and description of the scale fea- 

 tures and (2) the use of the atlas in racial and 

 other studies. 



USE OF THE ATLAS FOR AGE STUDIES AND 

 DESCRIPTION OF IMPORTANT SCALE FEATURES 



This section demonstrates the use of the atlas 

 to describe the physical features of the scale and 

 to determine the fresh-water, ocean, and total age 

 of the sockeye .salmon from its scales. Compare 

 the scale being studied with the plates in se- 

 quence, starting with plate 3. Compare the indi- 

 vidual features of the scale with the variations 

 shown on the appropriate reference plate. Select 

 the one that is most similar to the feature under 

 study. 



The scale shown in plate I is used here to il- 

 lustrate this method. Compare the scale in plate 

 I with the various reference plates as follows : 



Plate 3. Column A, chiefly regular, unbroken 

 circuli. 



Plate 4. First winter zone in the fresh-water 

 growth is of type 1. sharp, the second 

 is of type 2, moderately sharp. 



Plate 5. Fresh-water age 2., mediiun-sized 

 zone. 



Plate 6. A sharp transition from fresh-water 

 growth to ocean growth without plus 

 gi-owth. Type A (like fig. 1). 



Plate 7. First ocean gro\\i;h zone is of type 1 ; 

 circuli are chiefly unbroken and uni- 

 formly spaced. Second ocean gi-owth 

 zone is of type 2. "average." 



272 



U.S. FISH AND WILDLIFE SERVICE 



