SEAWARD MIGRATION OF CHINOOK SALMON. 37 



Table 36. — Young Chinooks from McCloud River, Baird, Calif., Sept. 24, 1909 — Continued. 



FORTY SPECIMENS •ft^TH NEW GROWTH. 



Length. 



Scale record. 



Average number of 

 rings— 



To new 

 growth. 



Of new 

 growth . 



Average length of 

 anterior radius — 



To new 

 growth. 



Total. 



Average 

 estimated 

 length of 



fish at 



beginning 



01 new 



growth. 



116 to 120 mm. 

 Ill to IIS mm. 

 106 to no m m . 

 101 to 105 mm . 

 96 to 100 mm . . 

 91 to 95 mm . . . 

 86 to 90 mm . . . 



Av. 99.5 mm , 



15.0 

 13-0 

 13.3 



13- 4 

 13.9 

 12.4 

 II. 8 



3-3 

 3-3 

 2.8 

 2.4 



43-' 

 43- 

 43- 

 40., 

 35- 

 36. 



61. o 

 SS-° 

 56. o 

 S2-3 

 so. 2 



43-7 

 44.9 



S°-S 



80.9 



It is interesting to note that the scale records to the beginning of the new growth 

 are approximately the same as the scale records of the fish which are equal in size to 

 the estimated length at the time of beginning the new growth (80.9 mm.). Table 36 

 shows that the scales of fish 81 to 85 mm. in length have an average of 13.5 rings and 

 an average length of 42.2. In the collection of specimens with new growth the average 

 number of rings preceding the new growth is 12.9, and the average length of the 

 anterior radius is 39.3. 



September 18, 191 1, 104 specimens were collected. Of these, 9 are mature males 

 averaging 99.6 mm. in length. The scales of these males have an average of 14.2 rings, 

 and the length of the anterior radius averages 50.7. None of the 95 immature fish had 

 begun the new growth, the scales of all terminating in winter rings. This is in striking 

 contrast to the condition found in 1909 when 53 per cent had started the new growth 

 by September 24. Evidently the conditions in the same locality may vary from year 

 to year in such a way as to materially alter the time for beginning the period of active 

 growth. The possible results of such annual fluctuation may be of considerable import- 

 ance in its effect on the future history of the fish. There are two possibilities: (i) The 

 fish may tend to migrate earlier in those years when the new growth is started earlier; 

 and (2) they may reach a greater size before migrating, but migrate at the same time 

 of year. A detailed study of the fish in some one tributary extending over a series of 

 years would be necessary to a solution to this problem. Careful attention should be 

 paid to fluctuations in climatic conditions. Fifty-one of the immature specimens in 

 this collection are males; 44, females. The males average 94.5 mm. in length; the 

 females, 91.8 mm. The following table {37) presents the data regarding the immature 

 specimens . 



