36 



Fishery Bulletin 103(1) 



1982-1983 



1983-1984 



Figure 1 



Scales from the 1982-83 and 1983-84 (smolt year through adult year) year 

 classes of coho salmon (Oncorhynchus kisutch) showing the axis of measurement, 

 the scale focus (F), ocean entry (OE), the annulus (A) at the end of the annual 

 ring and the scale margin (Ml. 



tween 1975 and 2002 were used to estimate growth 

 rates of maturing fish (Table 1). 



Scale measurements 



We measured the distances (mm) along the anterior-pos- 

 terior scale axis from the focus (F) to the last circulus 

 of the freshwater zone (ocean entry, OE), to the outside 

 edge of the winter annual ring (the "winter annulus," 

 A) when present, and to the margin (M), and also deter- 

 mined the total numbers and average spacing of circuli 

 in the ocean growth zone (Fig. 1). For certain scale 

 samples we also determined the spacing of every circulus 

 in the ocean growth zone of the scales or of the last few 

 circuli at the scale margin. 



Measurements of scales from juvenile fish caught 

 during research cruises 1981-85 were taken from im- 

 ages projected by a microfiche reader at a magnifica- 

 tion of about 88x and measurements of scales from all 

 other fish were acquired with image analysis software 

 (Optimas, vers. 5.1, Optimas, Inc., Seattle, WA, and 

 Image-Pro Discovery, vers. 4.5, Media Cybernetics, Sil- 

 ver Spring, MD) by using a CCD camera coupled to a 

 Leica compound microscope. All measurements were 

 calibrated from images of a stage micrometer. 



Circulus spacing and formation rate versus growth rate 



We used correlation and regression analyses to relate 

 average circulus spacing and formation rate to average 



scale and fish growth rate among year classes of juvenile 

 coho salmon during their first four or five months in the 

 ocean and among groups of maturing CWT coho salmon 

 during their entire ocean life (Table 2). We described 

 the relationships between the scale characteristics and 

 growth rate as power functions by using natural log 

 (In) transformed variables in linear regressions. Geo- 

 metric mean (GM) regression (Ricker, 1973, 1992; Sokal 

 and Rohlf, 1995) was used to relate the In-transformed 

 variables because they were subject to both natural 

 variability and measurement error and because our pur- 

 pose in the present study was to describe the functional 

 relationships between the variables and not to predict 

 one from the other. 



For each fish, rates of scale growth, fish growth, 

 and circulus formation in the ocean were estimated 

 as (SR-SR 0E )/Ad, (FL-FL 0E )IAd, and CIRC/Ad, re- 

 spectively, where SR = scale radius at capture, SR 0E = 

 scale radius at ocean entry (F to OE in Fig. 1), FL = 

 fork length at capture, FL ()A =estimated fork length at 

 ocean entry, C/.RC=the total number of circuli in the 

 ocean growth zone of the scale, and Ad = estimated days 

 between ocean entry and capture. Average spacing of 

 circuli was calculated as (SR LAST -SR 0E )/CIRC, where 

 SRj , lsr =the scale radius to the last circulus before the 

 scale margin. 



For juvenile fish, FL 0E was estimated by using the 

 Fraser-Lee back-calculation method (Ricker, 1992) and 

 the intercept from the FL-SR regression for ocean- 

 caught juvenile fish (34.16 mm. Fig. 2). However, be- 



