riods (July, September, and October) should 

 have scale growth of intermediate nature. 



First, let us examine a typical scale of an adult 

 Chinook that originated from May release (fig. 

 7). At the center of the scale, there are 14 

 closely placed fine circuli, which are followed 

 by more widely spaced coarser circuli. A check- 

 like structure (C) is present at the border be- 

 tween the two zones. Most of the fine circuli 

 represent intei-mediate growth that took place 

 after the fish was released, because young 

 Chinook released in May average only two to 

 three circuli on their scales. The zone of more 

 widely spaced coarser circuli that follows the 

 check represents what is generally regarded as 

 marine growth. It is bounded by a distinct band 

 of closely placed circuli (fig. 7, I). Both the 

 check (C) and the band (I) have the appear- 

 ance of an annulus. But since this is known to 

 be an age II fish (1957 release, 1959 returns), 

 and since the second annulus (II) is evident 

 near the resorbed margin of the scale, only 

 one of the two marks can be regarded as a 

 genuine annulus. Based on relative distance, 

 the band (I) should be regarded as the first 

 annulus. "C," therefore, is a sort of migration 

 check. The entire growth up to and including 

 the band (I), forms what is known as the 

 ocean nucleus. In the ocean nucleus, then, an 

 annulus in the fresh-water growth part is lack- 

 ing, and that gives rise to the age terminology 

 of "sub-one" for this group," or "O.", to use the 

 terminology of Koo (1962). 



Next, let us examine a tipical scale of an adult 

 Chinook that returned in 1960 from a February 

 1958 release (fig. 8). Here, there is also the 

 central crowded area of fine circuli (I) and the 

 surrounding wide marine growth that is bound- 

 ed by a band of closely placed narrow circuli 

 (II). Although "I" and "11" in this figure ap- 

 pear to be corresponding respectively to "C" 

 and "I" in figure 7, they are different in sig- 

 nificance. Because the fish was held in the 

 hatchery over the winter and was not released 

 until February, "I" in figure 8 is a true annulus, 

 not a mere check, as the "C" in figure 7. The 

 central area up to "I" forms what is known as 

 the stream nucleus and because the young fish 



s The term "sub-one" is derived from the subscript of Gilbert- 

 Rich's (1927) scale formula, for example, 3i, 4j. 



Figure 8. — A scale of adult chinook salmon that was 

 released as a finfrerling in February at the Little 

 White Salmon Hatchery (February 1958 release, 1960 



return). 



left fresh water during its second year, it is also 

 referred to as "sub-two age," or "1.", meaning 

 one annulus in fresh-water growth. This fish 

 is known to be age III, so there can be only two 

 marine annuli, which are labeled as II and III 

 in figure 8. The narrow band (i) between these 

 two annuli must therefore be regarded as an 

 incidental check. 



From the standpoint of age determination, 

 it is imperative that an ocean nucleus and a 

 stream nucleus can be positively identified, for 

 it will make a difference of 1 year in age, de- 

 pending upon whether an annulus or a check is 

 assigned to the central fine circuli area. No 

 definite criteria can be found in literature that 

 positively differentiate a mere check from a 

 genuine annulus in this nuclear area of growth 

 in chinook scales. Determination of age is usu- 

 ally based on the appearance of the nuclear zone 

 and is highly dependent upon personal judg- 

 ment. Thus, a stream nucleus has been de- 

 scribed as an area of many closely placed circuli 

 bounded by a distinct narrow band of more 



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U.S. FISH AND WILDLIFE SERVICE 



