CHINOOK SALMON MARKING, COLUMBIA RIVER 241 



rings similar to those inclosed by it. These two bands, representing the entire first 

 year's growth, form a fairly typical stream nucleus. The opposite extreme is illus- 

 trated by Figure .50. E.xcept for the small central portion of stream growth, this 

 scale is typical of the ocean type. The band following the first incidental check in 

 this case is more than twice the width of that in Figure 49, and the rings are spaced 

 more widely. This nucleus is fairly representative of a type very commonly found 

 among the chinook salmon of the Columbia River and for which the term "composite 

 nucleus" is proposed. This term will be used to designate nuclei comprised of both 

 stream and ocean growth. 



Many intergrading stages of composite nuclei are found among the scales of this 

 collectior. The transition from the typical stream type toward the ocean type is so 

 gradual as to make it impossible to divide the group of nuclei into two classes on the 

 basis of the presence or absence of ocean growth during the first year. Two nuclei 

 that fall about midway between the two extremes of variation are shown in Figures 51 

 and 52. Some of these intergrading stages probably involve estuary growth. A fish 

 may have spent a part of the first year in each of the thi'ee environments, or it may 

 have remained in the estuary dvu-ing the latter part of the first year. A second 

 incidental check, which is to be found in many of the nuclei, may represent the 

 change from the stream to the estuary or from the estuary to the ocean. 



Typical scales of adult fish in their fourth and fifth years are shown in Figures 

 53 and 54. These also show further variations in the composite type of nucleus. 



Returning now to a consideration of the scales of the mature fish in experiment 

 No. 3 we find nuclei similar to some of those in this collection. Eight adult fish were 

 recaptured, the scales of all of which have a central area that unquestionably is 

 stream growth. In all but one this area appears to represent nearly the entire first 

 year's growth but is not terminated by the winter check, which usually is found at the 

 margin of the stream type of nucleus. (See figs. 14 to IS.) This condition, combined 

 with the presence of rings of only moderate width surrounding the stream growth 

 suggests that the fish may have entered the ocean or at least the estuary before the 

 winter check was formed. The check at the twenty-third ring in Figures 17 and 18 

 may represent the winter check in that scale. In the others the boundary of the 

 first year's growth is not shown definitely. 



The stream growth in seven of these is broken by an incidental check at the fifth 

 to seventh rings. (See Table 4 and figs. 14 to 18.) The area inclosed by this check 

 evidently represents the margin of the scale at the time the fish were marked and 

 liberated. 



In the eighth scale of this collection (fig. 19) the stream growth extends only to 

 a point corresponding to the first incidental check in the other seven. From tfiis 

 point the rings widen gradually into the second year's growth, leaving no mark to 

 indicate the termination of the first year's growth. This nucleus is more typically 

 a composite type than are the other seven. 



