OBJECTIVE STUDIES OF SCALES OF COLUMBIA RIVER CHINOOK SALMON, 

 ONCORHYNCHUS TSHAW^YTSCHA (WALBAUM)' 



BY 



Ted S. Y. Koo,= Research Associate Professor, and Andhi Isarankura,^ Fisheries Biologist, FISHERY RESEARCH INSTITUTE, 

 College of Fisheries, University of Washington, Seattle,Washington 98105 



ABSTRACT 



This study uses an objective method that measures and 

 graphs the spacings of circuli. It also introduces a new 

 method of diflFerentiating ocean nucleus from stream 

 nucleus. Four groups of chinook salnlon scales were 

 studied, each with a specific purpose. 



First, scales from recoveries of two kinds of marked fall 

 chinook at Spring Creek National Fish Hatchery were 

 compared: one kind was from fish released as fry, and the 

 other from fish released as fingerlings. In the nuclear part 

 of scale growth, the group released as fry showed a larger 

 variance in spacing of circuli than the group released as 

 fingerlings but the difference in the mean values between 

 these two groups was not significant. In the first marine 

 part of scale growth, circulus spacing was significantly 

 wider in the group released as fry than in the group re- 

 leased as fingerlings. It was not possible, however, to 

 identify individual scales as coming from fish released as 

 fry or as fingerlings. 



Second, scales from marked and unmarked fall chinook 

 salmon at Spring Creek Hatchery were compared to see if 

 any effect of marking could be detected. Significant differ- 

 ences in circulus spacing in marine growth existed between 

 marked and unmarked fish, the latter having wider spac- 

 ings. Marking was in the removal of adipose and right 



pectoral fins from chinook fingerlings. This technique was 

 therefore regarded as having unfavorably affected the 

 growth of marked fish. 



Third, scales from marked fall chinook that had been 

 released at various times of the year at Little White Salmon 

 National Fish Hatchery were studied. The scales showed 

 that young chinook salmon released in May and July of the 

 first year grew an ocean nucleus typical of fall chinook; 

 those released in February of the second year grew a 

 stream nucleus typical of spring chinook; and those released 

 in September and October of the first year grew a nucleus 

 intermediate in character. 



Fourth, scales of fall and spring chinook salmon were 

 studied to see how these two groups could be identified by 

 their scales. Measurements of circulus spacing in the first 

 and second summer of marine growth revealed that, in the 

 spring chinook, marine circuli in both summers were about 

 equally wide; whereas, in the fall chinook, marine circuli of 

 the second summer were nearly one and one-half times 

 wider than those of the first summer. Thus, these scales 

 can be distinguished, not by nuclear growth as is normally 

 done by subjective judgment, but by relative marine growth 

 as measured by objective means. 



Since the early studies on the scales of 

 chinook salmon, Oncorhynchus tshawytscha 

 (Walbaum), by Gilbert (1914), Rich (1922), 

 Rich and Holmes (1929), and othei-s, little has 

 been published on the subject. Many problems 

 still deserve further study. The most important 

 and interesting problem is the classification and 

 identification of nuclear growth zones, the cen- 

 tral part of scale growth. Gilbert (1914) classi- 

 fies chinook scales into two types : those with an 

 ocean nucleus and those with a stream nucleus. 

 The ocean nucleus type originates from fish that 



1 Contribution No. 235, College of Fisheries, University of 

 ^Vashington. 



2 Present address: Chesapeake Biological Laboratory, University 

 of Maryland, Solomons, Md. 20688. 



3 Present address: Department of Fisheries, Bangkok, Thailand. 



FISHERY BULLETIN: VOL. 66, NO. 2 



Ptiblished April 1967. 



migrate seaward in their first year and thus has 

 the first annulus at the end of the first year's 

 marine growth; the stream nucleus type 

 originates from fish that do not migrate sea- 

 ward until the early months of the second year 

 and thus has the first annulus at the end of 

 fresh- water growth. To the former group be- 

 longs the fall run of chinook, which enters the 

 river from July through November; to the 

 latter, the spring run. which enters the river 

 from March to June. 



Classification of nuclear growth zones is very 

 useful and today still serves as the foundation 

 of age study of chinook salmon. This method is 

 most useful when only two groups of chinook 

 salmon are involved and their nuclear zones 



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