Relation of Scale Characteristics to River of 



Origin in Four Stocks of Chinook Salmon 



(Oncorhynchus tshawytscha) in Alaska 



By 

 RICHARD G. ROWLAND/ Fishery Biologist 



Bureau of Commercial Fisheries Biological Laboratory 

 Auke Bay, Alaska 99821 



ABSTRACT 



Differences in numbers of circuli and lengths of radii through the first fresh- 

 water annulus were used to test the hypothesis that the river of origin could be 

 determined from these characteristics. Analyses indicated that males and females 

 and different age groups of a brood year could be combined for each river, but that 

 comparisons between rivers should be restricted to common brood years. Although 

 average counts of circuli and average lengths of radii were different in sannples from 

 each river, the variability in these characteristics is great, and neither character- 

 istic is clearly diagnostic for the stock in any of the rivers. 



INTRODUCTION 



Historically, the chinook salmon ( Oncorhyn- 

 chus tshawytscha ) taken in the troll fishery 

 in southeastern Alaska originated mainly in 

 rivers of British Columbia, Washington, and 

 Oregon (Rich and Ball, 1935; Parker and 

 Kirkness, 1956). Catches of chinook salmon in 

 Alaska's troll fishery have declined drasti- 

 cally from a high of about 17 million pounds 

 in 1937 to about 4.5 million pounds in recent 

 years . 



Before fishery workers can effectively 

 nnanage the stocks to counter this decline, 

 they must be able to determine the river or 

 area of origin of individual fish. The pattern 

 of fresh-water growth on the scales is used 

 to determine the nnajor stocks or rivers of 

 origin for individual sockeye salmon(0. nerka ) 

 of the Fraser River system (Henry, 1961). I 

 hypothesized that the same method could be 

 used to identify the river of origin of chinook 

 salmon. As the first step in testing this 

 hypothesis I compared the growth pattern of 

 the fresh-water area of scales taken from 

 adult salmon returning to four widely separated 

 streams in Alaska. 



The scale samples came from chinook 

 salmon from the Taku, Alsek, Copper, and 

 Anchor Rivers (fig. 1), In the first three rivers. 



which are large, the fish were taken in com- 

 mercial gill nets set in the mouths of the 

 rivers. In the Anchor River, which is a much 

 smaller stream, the fish were captured on 

 sport fishing gear. 



Although several characteristics of a scale 

 reflect differences in the pattern of fresh- 

 water growth of a fish, I chose to count the 

 number of circuli and measure the lengths of 

 radii. Each of these characters was compared 

 to determine differences (1) between sexes, 

 (2) between age groups of a brood year, ^ (3) be- 

 tween brood years in each river, and (4) among 

 brood years in the four rivers. 



SELECTION AND PREPARATION OF SCALES 



The first scales formed during the fresh- 

 water growth of a salnnon are preferred for a 

 study of river of originbecause they provide the 

 best record of the fresh-water period of a 

 salmon's life. Brown and Bailey (1952) and 

 Clutter and Whitesel (1956) showed that scales 

 of salmonids form first along the posterior 

 half of the lateral line. I have observed this 

 type of scale development on juvenile chinook 

 salmon in Alaska. 



I used the scale at the intersection of the 

 second row of scales above the lateral line 



■""The author was drowned in a boating accident at Traitors 

 Cove, Alaska, in April 1964 in pursuit of his research. 

 This manuscript was completed by his colleagues. 



The term "brood year" describes the year of spawning of 

 the fish's parents. Salmon that spawn in 1967 produce the 

 1967 brood year. 



