20 



BULLETIN OF THE BUREAU OF FISHERIES. 



periphery of the scales. The average estimated length at the time of begimiing the 

 rapid growth is 39.3 mm. The whole collection contains 36 males and 33 females. The 

 males have an average length of 74.2 mm. and the females 74.8 mm. In the following 

 table (14) are presented the data relative to those specimens whose scales do not show a 

 band of intermediate rings: 



Table 14. — Data for 66 Young Chinooks from Crandall's Seining Ground, Sept. 15, 1916. 

 specimens without intermediate growth. 



Length. 



Scale record. 



Number 

 of rings. 



Length of 

 anterior 

 radius. 



86 to 90 mm. 

 81 to 8s mm. 

 76 to 80 mm. 

 71 to 75 mm. 

 66 to 70 mm. 

 61 to 6s mm. 

 56 to 60 nun. 



Av. 73.8mm. 



• 5.5 

 14.9 



13-4 

 12-9 



54. o 

 45. 1 

 42.0 

 4Z-0 



36. S 



33.5 

 33- o 



40. I 



Thirty-five young chinooks were taken by hook and line September 17, 1914, from 

 beneath the McGowan cannery at Ilwaco, Wash. The scales of 28 (80 per cent) of these 

 show a marginal band of intermediate rings. As a rule these intermediate rings are 

 distinctly heavier and wider than is the case with the average fish collected elsewhere 

 in the estuary. It is also found that the rings immediately preceding the intermediate 

 band are sometimes distinctly narrower than the more central rings. (See PI. II, 

 figs. 5 and 7.) This same appearance characterizes the scales of a few specimens from 

 Crandall's seining ground, just mentioned, and, to anticipate, is found in varying 

 proportions in all later collections from the estuary. There are not, however, two 

 distinct categories of scales, one exhibiting a distinct narrowing preceding the inter- 

 mediate growth and the other without such narrowing. All stages in the development 

 of this band of narrow rings may be observed from examples where the intermediate 

 band begins merely as a sudden widening (PI. II, fig. 6) to those where the intermediate 

 band is preceded by a very clear and well-marked band of narrow rings (PI. II, fig. 5). 

 Plate II, figure 7, represents an intermediate condition. Among the seven fish whose 

 scales do not show intermediate gro\vth are five whose scales terminate in narrow rings 

 of the winter type. These are somewhat smaller than the specimens whose scales do 

 show the intermediate band, and there can be little doubt that they are the more recent 

 arrivals from upstream which had not yet begun the intermediate growth. 



The scales of some of the specimens contained in this collection have also a more 

 or less well-developed primary check in addition to the migratory check which imme- 

 diately precedes the intermediate growth. This also is found in varying proportions 

 in the subsequent collections and will be considered more in detail later. Eighteen 

 males average 12 1.3 mm. in length and 17 females average 124.7 mm. The following 

 table (15) contains the data for this collection: 



