SEAWARD MIGRATION OF CHINOOK SALMON. 9 



the number of rings and in the length of the anterior radius as the size of the fish increases. 

 In comparison with the fry taken in March and April on the lower Columbia River, one 

 is impressed by the fact that all of these hatchery fish, even the smallest, are provided 

 with scales having well-developed rings. The smallest number of rings found on the 

 scales of any specimen was three. A considerable proportion of the wild fish less than 

 45 mm. and more than 40 mm. in length have no scales, or at most only platelets. It 

 seems likely that something in the conditions of life at the hatchery is responsible, but 

 no direct evidence proved that this is available. The scales of the larger specimens 

 have already acquired some of the characteristics of the scales of typical hatchery fish. 

 Compared with the scales of wild fish, those from hatchery specimens show an irregular 

 growth. There are frequent minor checks, indicated by narrower rings; but, as a rule, 

 the true winter check is less well marked. The rings themselves are frequently slender 

 and more or less broken. Plate I, figure 9, and Plate IV, figure 3, illustrate scales from 

 hatchery fish. It is possible that a careful study of these characteristics might give a 

 means of identifying adult fish which had been reared for the first few months under 

 hatchery conditions. 



In a collection of 26 fry from Cottonwood and Deer Islands, lower Columbia River, 

 on April 13, 1916, the average length of the specimens is 43.2 mm., with the mode at 

 38 mm. (See Table 3.) The skewing of the curve toward the smaller sizes is even 

 more marked in this collection than in the first one. The average length has increased 

 4.5 mm., but this seems largely due to the capture of several individuals which were 

 considerably larger than any contained in the first collection, the one made on the lower 

 river March 31 to April 2. The mode of the curve of length has remained the same. 

 No important changes appear in the scale record, although, as would be expected from 

 the larger average size of the fish, a slightly greater proportion has formed scales, and 

 the average number of rings is greater. 



Eighteen specimens were sexed. Males and females are in equal numbers, nine each. 

 The average length of the males is 42.3 mm. and of the females 44.1 mm. 



T.\Bi,E 3. — Fry from Cottonwood and Deer Islands, Lower Columbi.\ River, Apr. 13, 1916. 



66 to 70 mm . 

 61 to 6^ mm, 

 56to6omm. 

 51 to 55 mm. 

 46 to 50 mm.. 

 41 to 45 mm.. 

 36 to 40 mm.. 

 31 to 35 mm. 



Total 



Av. 43.2 mm. 



Length. 



Nmnher of speci- 

 mens with — 



Plate- 

 lets. 



Scales 

 with 

 rings. 



Scale record. 



Average 



number of 



rings. 



6.0 

 8.0 

 50 

 4.0 



2-3 

 2.0 



Average 

 length of 

 anterior 

 radius. 



23- o 

 23- o 

 ig.o 



25-5 



13.8 

 10. 5 



A small series of 19 specimens was preserved at the Clackamas hatchery May 2, 

 1916. (See Table 4.) The average length is 46.7 mm., with the mode at 48 mm. All 

 of the specimens have well-developed scales, none with less than four rings. 



