638 



Fishery Bulletin 88(4). 1990 



Table 1 



Fork length (PL, mm) vs. scale radius (SR. mm at 88 x): 

 Correlation coefficients (r) and geometric mean regressions 

 (GM. Ricker 1973) for age-0 fish held in saltwater tanks (A), 

 for age-1.0 jacks returning to Anadromous, Inc. in 1983 (B) 

 and 1985 (C), and for juvenile coho (ages 0.0 and 1.0) caught 

 in the ocean 1981-84 (D). 



Group 



GM regression 



A 

 B 

 C 

 D 



to the nearest mm fork length (FL), and a scale sample 

 taken from the preferred area (Clutter and Whitesel 

 1956). Each fish was also marked with a unique com- 

 bination of color spots above the anal fin by injecting 

 acrylic paint under the surface of the skin (Lotrich and 

 Meridith 1974). 



Fish were fed for 63-66 days. At the end of the 

 period fish were again anesthetized, measured and 

 weighed, and new scale samples were taken from the 

 preferred area, although sometimes on the other side 

 of the fish. Good scale samples were obtained from 80 

 fish at the beginning and end of the experiment. Mean 

 fish lengths at the beginning and end of this 63-66 day 

 period were 135 mm FL (SD 8.7, range 110-155 mm) 

 and 171 mm FL (SD 24.5, range 125-229 mm), respec- 

 tively. Acetate impressions were made of the scales. 

 All scale measurements were made at a magnification 

 of 88 X along the axis 20° ventrad of the posterior- 

 anterior axis of the scale. 



Scales from each fish taken at the beginning and end 

 of the experiment were compared to determine the 

 spacing and number of circuli laid down during the 

 intervening growth period. Mean circulus spacing 

 during the growth period was calculated as (SR-^ - 

 SRi)/n, where SRv is the radius to last scale circulus, 

 SRi is the radius to last circulus before the growth 

 period as determined by comparison with the initial 

 scale sample, and n is the number of new circuli formed 

 during the growth period. Rate of circulus formation 

 for each fish was also determined (»/d, where d is the 

 duration of the experiment in days). 



Linear growth rate was calculated for each fish as 

 (FL2 - FLi)/d, where FL, and FLo are the lengths 

 (mm) at the beginning and end of the experiment, 

 respectively. Scale growth rate was also calculated as 

 (SR,,,( - SRi)/d, where SR,,,, is the total scale radius. 



75 100 125 150 175 200 



SCALE RADIUS (mm at 88X) 



Figure 1 



Fork length vs. scale radius scattergranis and GM regression lines 

 for age-0 smolts held in saltwater tanks (O, — ), for age-1.0 CWT 



jacks returning to Coos Bay in 1983 (D. ) and 1985 (<>, --), 



and CWT juvenile fish caught in the ocean (A, -•■-). 



Returning jacks 



Fork length was measured and scale samples taken 

 from the preferred area of 64 and 99 coded-wire tagged 

 (CWT) jacks (precocious males) within 2 or 3 days 

 of their return in 1983 and 1985, respectively, to the 

 Anadromous Inc. facility on Coos Bay. Scales had also 

 been taken earlier from a subsample of each release 

 group shortly before their release as smolts. Fork 

 length at time of ocean entrance was backcalculated 

 for each returning jack using the relationship between 

 scale radius and fork length at the time of release for 

 that group and other groups released in the same 

 month. (Tag groups were grouped by month of release 

 to obtain adequate numbers for the prerelease scale 

 radius-fish length relationships). Ocean entrance was 

 detected on the scale as an abrupt change in circulus 

 spacing (see Fisher and Pearcy, 1988). Since these fish 

 were released and returned to a site only 8 km from 

 the ocean, their period of growth in the ocean should 

 be very similar to the time between their release and 

 return. Growth rate of each fish while in the ocean was 

 estimated by (FL^ - FLi)/d, where FL-j is length on 

 return to the hatchery, FL; is the backcalculated 

 length at time of ocean entry, and d is the days between 

 release and return. Scale growth rate was estimated 

 as (SRt„t - SRi)/d, where SRI is the scale radius to 

 the ocean entrance mark, and SR,,,, is the total scale 

 radius. Mean circulus spacing during the ocean growth 

 period was calculated as the distance between the first 

 and last ocean circulus divided by « - 1, where n = the 

 number of circuli laid down during ocean growth. 



