Fisher and Pearcy: Seasonal changes in growth of Oncorhynchus kisutch off Oregon and Washington 41 



Spacing = 0.839 ■ScaleCrouvthRate 613 . n - 9. r= 0.88. I 2 = 0.78 



a) 



E 020 



0) 



S> 017 



CircRate= 2 03V ScaleGrowthRale 0502 .n = 9, r=0.74, ^ = 0.55 



0.007 008 009 0.010 011 



Scale growth rate (mm/d) 



Figure 3 



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

 ing of ocean circuli and (B) estimated average rate of circulus 

 formation for nine year classes (see Table 2) of juvenile coho 

 salmon (O. kisutch) caught in the ocean in research nets in 

 August (1981) or September (1982-84 and 1998-2002; black 

 symbols, ±2 SE). Regressions are GM linear regressions of 

 In-transformed variables (presented in their power function 

 form). 



tained by juvenile coho salmon during their first sum- 

 mer, fall, and winter in the ocean. 



Do the seasonal changes in circulus spacing in the 

 ocean growth zones of scales coincide with similar sea- 

 sonal changes in growth rates of juvenile and maturing 

 coho salmon? In Figure 6 we plotted the average lengths 

 of juvenile and maturing coho salmon from all research 

 cruises 1981-2002 and the average apparent growth 

 rates of coho salmon during different seasons (dashed 

 lines). Apparent average growth rate of juvenile coho 

 salmon between June and September was 1.30 mm/d, 

 about twice the apparent growth rate of 0.64 mm/d 

 between September and the following May. Apparent 



growth rates of maturing fish between late May and 

 late June was very rapid (2.11 mm/d), about twice as 

 great as the apparent growth rate of maturing fish later 

 between June and September (1.01 mm/d). 



In a general sense, this pattern of changing apparent 

 growth rate over time in the ocean corresponds well to 

 the pattern of changing circulus spacing seen in Fig- 

 ure 5, A-E. The rapid growth of juvenile coho salmon 

 between June and September occurs during a period 

 when the spacing of circuli generally is high (Fig. 5E). 

 When maturing fish were caught in the ocean fisheries 

 in late June and in July and August a zone of widely 

 spaced circuli already was present on the scales (Fig. 5, 



