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 fry 

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

 show this type 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 (80 in number) average 75.2 mm. in length. The length ranges from 53 to 105 

 mm., wth 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. 1 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 : 



T.\blE 9. — Fry from Columbl^ Estu.\ry, June 12 and 13, igi6. 

 EIGHTY SPECIMENS •ft^THOUT INTERMEDIATE GROWTH. 



Length. 



Scale record. 



Average 



number of 



rings. 



Average 

 length of . 

 anterior 

 radius. 



101 to 105 mm. 

 96 to ICO mm... 

 91 to 95 mm .... 



86 to 90 mm 



81 to 85 mm 



76 to 80 mm 



71 to 75 mm 



66 to 70 mm 



6r to 6s mm 



56 to 60 mm.... 

 51 to ss mm 



Av. 7s.anjm. 



II. o 



13. S 

 11-3 



10. S 



20. I 



9-3 

 9-0 

 7-6 

 7-0 

 40 



9.6 



48.0 



SO. s 

 43.6 

 41.9 

 38- o 

 36.7 

 3S-0 

 30.8 



38- g 



38.0 



38.1 



SIXTEEN SPECIMENS WITH INTERMEDIATE GROWTH. 



91 to 95 mm. 

 86 to 90 mm., 

 Si to 85 mm.. 

 76 to 80 mm. 

 71 to 7smm., 

 66 to 70 mm. 



Av. 83.1 mm. 



I,engtli. 



Scale record. 



Number of rings — 



4.6 



16.9 

 19.0 

 14.6 

 14.0 



13. S 

 IJ.O 



16.3 



Length of anterior 

 radius — 



To inter- 

 mediate 

 growth. 



33- o 

 36.3 

 36.0 

 35- 5 

 33- o 

 33- O 



36. 7 



Total. 



S«-3 

 46-3 

 43. o 

 38.0 

 33- o 

 33- O 



Average 

 estimated 

 length of 



fish at 

 beginning 

 of inter- 

 mediate 

 growth, o 



63.0 

 49.6 

 S3.0 

 S30 

 50.5 

 48. S 



53-3 



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



75412°— 22 2 



