SEAWARD MIGRATION OF CHINOOK SALMON. 



13 



growth in sockeye and silver salmon which migrated as yearlings. These intermediate 

 rings represent a period of growth more rapid than the normal growth in fresh water 

 and yet not so vigorous as the true ocean growth (PI. II, figs. 3, 4, 5, and 6). Inter- 

 mediate rings are not present on the scales of every specimen, but among the larger frj- 

 and yearlings taken in the estuary after the first of June some are always found which 

 show this tj^pe of growth at the margins of the scales. For the purpose of ready com- 

 parison those fish whose scales show the band of intermediate rings are given separate 

 consideration. 



The fry contained in the collection of June 13 which do not show this intermediate 

 growth (So in number) average 75.2 mm. in length. The length ranges from 53 to 105 

 mm., with the mode at 73 mm. The average number of rings is 9.6, and the average 

 length of the anterior radius is 38.1. The males number 35 (44 per cent) and average 

 78.3 mm. The 45 females average 72.8 mm. in length. 



Sixteen specimens have scales which show the intermediate growth. These average 

 83. I mm. in length. Seven males average 80.3 mm. ; and 9 females, 85.3 mm. The follow- 

 ing table (9) presents the data for this collection: 



Table g. — Fry from Columbia Estu.\ry, June 12 and 13, 1916. 

 EIGHTY SPECIMENS WITHOUT INTERMEDIATE GROWTH. 



Length. 



Scale record. 



Average 



number of 



rings. 



Average 

 length o( 

 anterior 

 radius. 



loi to 105 mm. 

 96 to loo m m .. 

 91 to 95 mm... 

 86 to 90 mm... 

 81 to 85 mm... 



76 to 80 mm 



71 to 75 mm... 

 66 to 70 mm... . 

 61 to 65 mm... 

 56 to 60 mm.. . 

 51 to 55 mm 



Av. 75. « mm. 



13. S 



XI. a 

 10.5 

 10. z 

 9. J 

 9.0 

 7-6 

 70 

 40 



9-6 



48.0 



SOS 

 43.6 

 41.9 

 38.0 

 36.7 

 3S-0 

 30.8 

 98.8 

 38.0 



38.1 



SIXTEEN SPECIMENS WITH INTERMEDIATE GROWTH. 



o For explanation of estimated length of fish in this and succeeding tables see p. 14. 

 75412°— 22 2 



