160° 



150° 



140° 



130° 



65<: 



60° 



55<= 

 N. 



Figu 



65° 



60° 



- 55° 



W. 160° 



150° 



KO'^ 



\iO° 



re 1. — Four rivers in Alaska where scale characteristics of Chinook salmon were studied to distinguish river 



of origin. 



and the diagonal row of scales that originates 

 at the insertion of the dorsal fin. This location 

 on the body of the salnnon was selected by the 

 International Pacific Salmon Fisheries Com- 

 mission for collecting scales to be analyzed 

 (Clutter and Whitesel, 1956) and has proved 

 to be satisfactory (Henry, 1961). If the selected 

 scale was regenerated, it was replaced from 

 a group of additional scales taken from above 

 the lateral line in the immediate area. The 

 substitution of these scales seems justified 

 by similarity of counts of circuli of scales 

 from this area (Clutter and Whitesel, 1956). 



The selected scale was attached to a gummed 

 card, and 6 to 12 adjacent scales were placed 

 in an envelope for use if the first scale sub- 

 sequently proved to be regenerated. Later 

 the scale was cleaned, examined under a 

 microscope, and transferred to a new gummed 

 card- -or replaced, if it was regenerated. 

 Plastic impressions of the scales were made 

 by the technique developed by Koo (1955) and 

 Clutter and Whitesel (1956). 



EXAMINATION OF SCALE 

 CHARACTERISTICS 



I determined the scale characteristics -- 

 numbers of circuli and lengths of radii--only 

 for scales with one fresh-water annulus and 

 included only the first year's growth (platelet 

 through first annulus). Scales with no fresh- 

 water annulus or those with two were relatively 



few and were not used because of the possi- 

 bility that the fresh-water growth of the scale 

 during the first year might be affected by the 

 length of time the fish was in fresh water. 

 Age determinations, counts, and measurements 

 were made on an image of the scale impression 

 projected at a magnification of SOX. 



I determined the age of the fish sampled by 

 counting annuli on the scales. A 2-digit symbol 

 was used to express age by the method of 

 Gilbert and Rich (1927). A superscript denotes 

 the age at which the fish was captured and a 

 subscript the year of life in which the fish 

 migrated to sea. For example, a 52 fish is in 

 its fifth year of life (has four annuli on its 

 scales) and migrated to sea in its second year 

 (had one annulus when it entered the ocean). 



I used the methods of Clutter and Whitesel 

 (1956) for counting the circuli and measuring 

 the radii. Starting from but not including the 

 innermost circulus, all circuli to the outer 

 edge of the first fresh-water annulus were 

 counted. The outer edge of the first annulus 

 was considered to be at the point where the 

 space between circuli began to increase. The 

 length of the radius is the distance from the 

 innermost circulus (the margin of the focus) 

 to the outer edge of the first fresh-water 

 annulus and is measured along a line extending 

 ventroanteriorly from the focus at an angle 20 

 degrees from the horizontal axis of the scale. 

 All measurements were of the projected image 

 to the nearest millimeter. 



