642 



Fishery Bulletin 88(4), 1990 



year and that during the coldest months widely spaced 

 circuli were formed. Hogman (1968) cited work by 

 Deason and Hile (1947) that indicated that annuii and 

 checks formed in scales of kiyis living at depth in Lake 

 Michigan, despite a very small annual variation in 

 water temperature (2-3°C). Bhatia (1932) cited his 

 earlier work showing that when rainbow trout were fed 

 uniformly throughout the year no periodic zones were 

 formed on their scales and all rings were of nearly the 

 same width despite fluctuations in temperature. How- 

 ever, there is some evidence that in brown trout water 

 temperature during egg and alevin stages prior to scale 

 formation affected subsequent rate of circulus forma- 

 tion (Skurdal and Anderson 1985). 



Inherent differences between groups of fish may 

 mask the relationship between circulus spacing and 

 growth rate. For example, for coho jacks returning to 

 the Anadromous Inc. facility in Coos Bay in 1985, 

 scales were generally smaller at a given fish length 

 (Fig. 1), and rate of circulus formation was lower at 

 a given growth rate (Fig. 2), than was the case for CWT 

 juveniles caught in the ocean. This resulted in signif- 

 icantly different mean spacing of circuli in these two 

 groups (3.86 vs. 4.04, ^test, p<0.05) despite very 

 similar mean growth rates (1.53 and 1.49 mm/d, ^test, 

 n.s.). Because of differences in the relationships be- 

 tween circulus spacing and growth rate among dif- 

 ferent groups of juvenile coho salmon, inferences about 

 relative growth rates based on scale circulus spacing 

 are probably only valid when made between groups 

 that are similar in age, size, and morphometric char- 

 acteristics (i.e., very similar SR-FL relationships). 



Data from the group of subyearling fish held in salt- 

 water tanks suggest that the relationship between cir- 

 culus spacing and growth rate may be complicated. A 

 third-order relationship (see footnote. Table 3) gave a 

 better fit to the data than did a simple linear relation- 

 ship. In this group of fish there was little change in cir- 

 culus spacing between growth rates of 0.4 and 0.9 

 mm/d. More rapid changes in circulus spacing with 

 growth rate occurred both above and below this range 

 (circles, Fig. 4). This result suggests that for coho 

 salmon there may be ranges of growth rates within 

 which circulus spacing is a poor indicator of relative 

 growth rate. 



We compared mean circulus spacing in the ocean 

 growth zone of scales for unmarked yearling (age 1.0) 

 juvenile coho caught in the ocean in late summer of 

 1981, 1982, 1983, and 1984 (Fisher and Pearcy 1988). 

 These fish had very similar SR-FL relationships in all 

 years and were of similar size at time of entry into the 

 ocean (based on backcalculated size at ocean entry). We 

 also estimated gi-owth rates of these unmarked juvenile 

 yearling coho salmon between early and late summer 

 (between .June and August or September) from changes 



in mean lengths with time (see Fisher and Pearcy 1988, 

 their Table 3). Rank order of mean spacing between 

 circuli and growth rates estimated from shifts in mean 

 FL with time are compared in Table 6. Although the 

 rank orders do not agree in detail, they both suggest 

 higher fish growth rates during the summers of 1981 

 and 1982 than in 1983 and 1984. 



Acknowledgments 



We thank Ron Gowan of Anadromous, Inc. for his 

 cooperation and for supplying data and scale samples 

 from returning jacks. We also thank Ric Brodeur, Alton 

 Chung, Harriet Lorz, Jon Shenker, Jamie Trautman, 

 and Waldo Wakefield for their help with various as- 

 pects of this project. This research was supported by 

 the Northwest and Alaska Fisheries Center (NA-88- 

 ABH-00043 and NA-85-ABH-00014) and the Oregon 

 State University Sea Grant College Program (NA 

 881AAD-D-00086, R/OFP-17). 



Citations 



Barber, W.E.. and R.J. Walker 



1988 Circulus spacing and annulus formation: Is there more 

 than meets the eye? The case for sockeye salmon, OhcoWij/w- 

 rhiis tifrka. .J. Fish Biol. 3:237-245. 

 Bhatia, D. 



1932 Factors involved in the production of annual zones on 

 the scales of the rainbow trout {Saliiio irideus). II. J. Exp. 

 Biol. 9:6-11. 

 Bilton, H.T. 



1975 Factors influencing the formation of scale characters. 

 Int. North Pac. Fish Comm. Bull. 32:102-108. 

 Bilton. H.T., and G.L. Robins 



1971a Effects of feeding level on circulus formation on scales 

 of young sockeye salmon {Onmrhynchiis twrka). J. Fish. Res. 

 Board Can. 28:861-868. 



