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



37 



cause of allometry in the FL-SR relationships of juvenile 

 and maturing fish (Fig. 2), which a ln-ln transformation 

 of the data failed adequately to correct, the Fraser-Lee 

 method was not used to estimate FL OE of the maturing 

 fish caught in the ocean. Instead, FL OE of maturing 

 fish was estimated by direct substitution of (SR OE ) into 

 the GM regression relationship between FL and SR for 

 juvenile coho salmon caught in the ocean 1981-85 and 

 1998-2001 (gray regression line. Fig. 2). 



For juvenile fish caught in August or September, Ad 

 was estimated as the capture date minus 25 May, a date 

 near the peak of coho salmon smolt migration in the 

 Columbia River estuary (Dawley et al., 1985a). Because 

 we used a single date of ocean entry for all fish, errors 

 in estimated growth rates of some individual juvenile 

 coho salmon probably were quite large; the timing of 

 ocean entry of fish can vary by as much as two months. 

 However, for the correlation and regression analyses we 

 used growth rates averaged by year class, which were 

 probably quite accurate, if the average date of ocean 

 entry of the fish in the samples is assumed to be similar 

 across years. In the Columbia River, the major source 

 of juvenile coho salmon on the Oregon and Washington 

 coasts, ocean entry was concentrated between late April 

 and early June and the timing of ocean entry varied 

 little between years (Dawley et al., 1985a). 



Dates of ocean entry of the maturing CWT Sandy 

 and Cowlitz hatchery coho salmon (Table 2) were esti- 

 mated from the hatchery release dates and the rates of 

 downstream migrations of these fish observed during 

 extensive sampling of migrating smolts at rkm 75 in the 

 upper Columbia River estuary (Dawley et al., 1985b). To 

 estimate dates of ocean entry of the Fall Creek hatch- 

 ery fish, for which data on downstream migration were 

 lacking, we assumed that smolts migrated to the ocean 

 from the different release sites at the same average rate 

 of downstream migration as that of Cowlitz Hatchery 

 fish released in late April (5.7 km/d). 



Potential errors in estimated growth rates of matur- 

 ing CWT coho salmon caused by inaccurately estimat- 

 ing size of fish at ocean entry, or date of ocean entry, 

 were proportionally very small when compared to the 

 total amount or duration of ocean growth. At a typical 

 SR 0E of around 0.7 mm, the 95% prediction limits for 

 FL from the SR-FL regression of juvenile fish (Fig. 2) 

 are about ±31mm. An error in size at OE of 15-30 mm 

 would only be 2-10% of the estimated total growth in 

 FL in the ocean of the maturing fish (320 mm-610 mm). 

 Similarly, an error in estimated date of ocean entry of 

 30 days would equal only about 6-10% of the total time 

 that the fish was in the ocean (336-535 d). Errors for 

 the group-averaged data used in our correlation and 

 regression analyses were probably much lower. 



Seasonal changes in spacing of circuli 



To investigate whether circulus spacing and growth 

 rate were correlated seasonally, we first described the 

 patterns of seasonally changing circulus spacing of 

 juvenile and maturing coho salmon in the ocean and 



Table 2 



Nine year classes of juvenile coho salmon caught in 

 research nets in August or September and 17 groups of 

 CWT maturing coho salmon caught in the Oregon ocean 

 fisheries used in the correlation and regression analyses 

 of scale characteristics and growth rate. CWT maturing 

 fish were from three hatcheries (Fall Creek "F" on the 

 northern Oregon coast and Sandy "S" and Cowlitz "C" in 

 the lower Columbia River basin) and were released from 

 hatcheries during three periods. 



Capture year 



Hatcheries 



Numbers offish 



CWT maturing fish released late April 

 or early May (days 119-127) 



1982 F, S 



1983 F, S, C 



1984 S, C 



1985 S, C 



1986 S 



1987 S 



1989 S 



1990 S 

 CWT maturing fish released in March (days 74-76 



1984 F 31 



1985 F 21 



CWT maturing fish released in late May or early 

 Juneldays 151-157) 



1991 S 30 



1992 S 77 



11, 15 

 34, 17, 51 

 52,35 

 12,26 



67 

 94 

 57 



18 



Juvenile fish 

 1981 

 1982 

 1983 

 1984 

 1998 

 1999 

 2000 

 2001 

 2002 



99 

 95 

 81 

 88 

 13 

 60 

 75 

 67 

 123 



then compared these patterns of changing circulus 

 spacing to changing fish growth rates. Because the 

 widths of the pre-annulus and postannulus scale zones 

 and the numbers of circuli in each zone varied greatly 

 among individual fish and among groups of fish, we 

 described circulus spacing in each of 25 equally spaced 

 intervals between OE and the annulus and in each of 

 25 equally spaced intervals between the annulus and 

 the scale margin, rather than on a circulus by circulus 

 basis. Specifically, the pre-annulus and postannulus 

 ocean zones of scales were each divided into 25 equal 

 intervals, and the radial distance from OE to the upper 

 bounds of each of the intervals was determined. Next, 

 the numbers of ocean circuli between OE and the upper 

 bounds of each of the 50 intervals were interpolated. 

 For example, if a boundary fell 25% of the distance 



