42 



Fishery Bulletin 103(1) 



E 



E. 0050 



Spacing =0 61 7'ScaleGrowthRate 



□ 

 A 



o 



o 



Cowlilz.rel days 123-124 



Fall Creek, rel. days 121-122 



Fall Creek, rel days 74-76 



Sandy, rel days 119-127 



Sandy, rel days 151-157 



0040 0045 0050 0055 0060 0065 0070 0.0075 0060 



CircRate = 6 61 b' ScaleGrowthRate 

 n=17. /-=087, i 2 = 0.75 



B 



0.0040 0.0045 0.0050 0.0055 0.0060 0.0065 0070 0.0075 0080 



Scale growth rate (mm/d) 



Figure 4 



Estimated average scale growth rate versus (A) average spac- 

 ing of ocean circuli and (B) estimated average rate of circu- 

 lus formation for 17 groups (see Table 2) of maturing coho 

 salmon (O. kisutch) caught in the Oregon ocean fisheries 

 (±2 SE). Regressions are GM linear regressions of In-transformed 

 variables (presented in their power function form). Data for 

 Sandy Hatchery fish caught in 1983 and 1984 are labeled as 

 examples of year when average growth rates were extremely 

 different. 



A-C), indicating that these widely spaced circuli were 

 produced earlier during the period of apparently rapid 

 growth in the spring and early summer (Fig. 6). Circu- 

 lus spacing at the scale margin was already declining 

 in July among maturing fish in some years (Fig. 5A), 

 and was clearly lower among maturing fish caught in 

 August or September (Fig. 5, B and D) indicating that 

 these more narrowly spaced circuli were produced some- 

 time during the apparently slower growth of maturing 

 fish between late June and September (Fig. 6). Finally, 

 the low spacing of circuli in the annual ring occurs 

 sometime between late September of the first year and 



mid-May of the second year, which was also the period 

 of lowest apparent growth rate (Fig. 6). 



The pattern of changing circulus spacing at the scale 

 margin is most clearly seen when average spacing of the 

 outer two circulus pairs is plotted against the average 

 Julian day of capture (Fig. 7, A and B). Among juvenile 

 fish caught in research nets, the average spacing of the 

 circuli at the scale margin was narrower in September 

 than in June (Fig. 7A, see also Fig. 5E). We lack suf- 

 ficient FL data from mid and late summer to deter- 

 mine whether or not a decrease in the average growth 

 rate of juvenile fish was associated with the observed 



