closely spaced circuli, the annulus. An ocean 

 nucleus, on the other hand, is recognized when 

 the nuclear zone consists of relatively few but 

 wider circuli that are not marked off by a dis- 

 tinct check from the ensuing widely spaced ma- 

 rine growth. 



Unfortunately, nuclear zones of many Chi- 

 nook salmon scales are not clearly defined so 

 that the morphology of the nuclear zones alone 

 does not enable us always to differentiate with 

 certainty the ocean nuclei from the stream 

 nuclei. If, for example, the scales in figures 7 

 and 8 had come from fish of unknown age, we 

 would have no real basis for calling one mark 

 a mere check (C) and the other a true annulus 



(I). 



Obviously, something other than visual deter- 

 mination must be devised. As we had avail- 

 able a large number of scale samples from re- 

 captured marked chinook salmon comprising 

 both the stream type and the ocean type of 

 nuclear growth, we were able to compare the 

 characters of these two groups of scales on a 

 quantitative basis. Because the nuclear zones 

 of circuli failed to show significant differences, 

 our study was extended to cover marine growth 

 as well, and we have developed some criteria 

 that help to guide the chinook scale reader to 

 differentiate ocean from stream nuclei on a 

 more objective basis. 



Before we discuss quantitative measure- 

 ments, let us examine some scales of adult 

 chinook that originated from releases during 

 the intermediate period between May of the 

 first year and February of the next year, to 

 observe the transition from ocean nucleus 

 growth type to stream nucleus growth type. 



A scale of a July release origin is shown in 

 figure 9. Being similar to the scale of a May 

 release origin (fig. 7), it also shows an ocean 

 nucleus (I) and a strong check (C) for the 

 nuclear area. Based on the known age of this 



Figure 10. — A scale of adult chinook salmon that was 

 released as a fingerling in September at the Little 

 White Salmon Hatchery (September 1958 release, 

 1960 return). 



Figure 9. — A scale of adult chinook salmon that was 

 released as a fingerling in July at the Little White 

 Salmon Hatchery (July 1957 release, 1959 return. 





Figure 11. — A scale of adult chinook salmon that was 

 released as a fingerling in September at the Little 

 White Salmon Hatchery (September 1957 release, 

 1960 return). 



SCALES OF CHINOOK SALMON 



175 



