Fisher and Pearcy Scale circulus spacing in Oncorhynchus kisutch 



639 



X 



oo 



o 



a: 

 o 



10 



20 



30 



40 



50 



60 



TOTAL FISH GROWTH (mm) 



70 



80 



Table 2 



Rate of circulus formation (RCF, circuli per day) vs. fish 

 growth rate (GR, mm/d): Correlation coefficients (r), prob- 

 ability that correlation = 0.0 (jt) ), and geometric mean regres- 

 sion (GM) for age-0 fish held in saltwater tanks (A), CWT jacks 

 (age 1.0) returning in 1983 (B) and 1985 (C), and CWT juvenile 

 fish (both age 0.0 and 1.0) caught in the ocean (D). 



Group 



GM regression 



A 80 0.89 <0.01 RCF = 0.18 -(GR) -I- 0.03 



B 64 0.58 <0.01 RCF = 0.10 (GR) -I- 0.03 



C 99 0.57 <0.01 RCF = 0.10 (GR) -I- 0.00 



D .34 0.84 <0.01 RCF = 0.12 (GR) -I- 0.02 



Figure 2 



Scale growth vs. fish growth scattergram and GM regression line 

 for individually marked age-0 smolts held in saltwater tanks. 



Juvenile coho collected in the ocean 



Growth rates in the ocean were estimated for CWT or 

 spray-marked juvenile coho released (a) very near the 

 ocean in Yaquina and Coos Bays and caught 60 or more 

 days later in the ocean in August or September (15 

 fish), and (b) in the Columbia River (19 fish) and 

 sampled during downstream migration near the ocean 

 (at rkm 75, Dawley et al. 1985) and caught in the ocean 

 60 days or more after the median fish passed rkm 75, 

 or released below rkm 75 and caught at least 60 days 

 later in the ocean. For fish released in Yaquina or Coos 

 Bays growth rate was estimated by (FL^. - FLi)/d 

 where FLj is the length at ocean entrance backcalcu- 

 lated from scales using a regression of FL on scale 

 radius from a sample of fish taken at the time of 

 release, FL? is length at capture in the ocean, and d 

 is days between release and recapture. For Columbia 

 River fish released in 1981, 1982, 1983, and 1984 length 

 at ocean entrance was backcalculated using a regres- 

 sion of FL on scale radius derived from fish collected 

 at rkm 75 in 1982 and 1983, combined. The number 

 of days in the ocean was estimated from the date the 

 median fish in each group passed rkm 75 and the mean 

 downstream migration rates for each group. Estimated 

 date of ocean entry for each group ranged from 3 to 

 11 days following passage of the median fish at rkm 

 75. For CWT Colimibia River fish caught in 1984, when 

 no sampling occurred at rkm 75, average downstream 

 migration rates for tag groups from the same hatch- 

 eries in 1981-1983 were used in estimating ocean en- 

 trance date and days in the ocean (d). Scale growth rate 

 for juvenile coho caught in the ocean was estimated the 

 same way as for jacks. 



Results 



Fork length was positvely and significantly correlated 

 with scale radius (SR) in all groups (Table 1, Fig. 1). 

 The relationship (geometric mean regression, Ricker 

 1973) for each group of fish appeared linear. However, 

 SR was smaller relative to FL for jacks returning in 

 1985 (diamonds in Figure 1) than for jacks returning 

 in 1983 (squares) or for CWT juvenile coho salmon col- 

 lected in the ocean (solid triangles). In addition, almost 

 all FL-SR data points for returning yearling jacks and 

 juveniles caught in the ocean were above the extrap- 

 olated regression line for the smaller subyearling fish 

 held in saltwater tanks (Fig. 1). Thus, the relationships 

 between FL and SR varied between age or size groups 

 (small subyearling fish vs. larger yearling jacks and 

 juveniles caught in the ocean) and between years (1983 

 vs. 1985 Anadromous Inc. jacks). The relationship be- 

 tween scale growth and fish growth appeared linear 

 for the subyearling coho smolts held in saltwater tanks 

 (Fig. 2). 



Rate of circulus formation was positively and signif- 

 icantly (r = 0.57 - 0.89, jD<0.01) correlated with fish 

 growth rate for all groups (Table 2, Fig. 3). However 

 the slope of the relationship was lower for ocean-caught 

 juveniles and jacks returning in 1983 and 1985 (slopes 

 of GM regression = 0.12, 0.10, 0.10, respectively) than 

 for the subyearling fish held in saltwater tanks (slope 

 = 0.17) At similar fish growth rates, rates of circulus 

 formation were generally higher for the subyearling 

 fish held in saltwater tanks than for juveniles caught 

 in the ocean or for returning jacks (Fig. 3). 



The spacing between circuli was positively and 

 significantly correlated with fish growth rate for all 

 groups but jacks returning in 1983 (Table 3). The cor- 

 relation was strong (r = 0.80) for age 0.0 fish held in 

 saltwater tanks, but much weaker for jacks returning 

 in 1985 (r = 0.24). However, the relationship between 

 circulus spacing and fish growth rate for subyearling 



