SEAWARD MIGRATION OP CHINOOK SALMON. 

 Table 6. — Fry from Lower Part of Columbia Estuary, May ii, 1916. 



II 



81 to ^5 nun. 

 76 to 80 nun . . 

 71 to 75 nun. 

 66 to 70 mm., 

 61 to 65 mm. 

 56 to 60 mm.. 

 51 to 55 mm. 

 46 to 50 nun . 

 4t to 45 mm 

 36 to 40 nun , 

 31 to 35 mm. 



Total. 



Av. 47.7 mm. 



Length. 



Ntunber. 



Ninnber of speci- 

 mens with — 



Plate- 

 lets. 



Scales 

 with 

 rings. 



89 



Scale record. 



Average 



number of 



rings. 



6.5 

 6.1 

 S-4 

 4.0 

 3-J 

 1.6 



Average 

 length of 

 anterior 

 radius. 



33.0 

 39. o 

 24.9 

 31.3 

 "7-3 

 10.5 



In comparing these collections with the ones made the day before, the average 

 smaller size of the fish is the only conspicuous point of difference. This is obviously 

 due to a scarcity of fish of the larger sizes, since the modes of the two curves are the 

 same, 43 mm. The water in the lower part of the estuary is quite brackish owing to 

 the considerable admixture of salt water, while that in the part of the river where the 

 collections of May 10 were made is perfectly fresh. Therefore it would seem probable 

 that on reaching the brackish water the larger fish tended to continue their migration 

 on into the ocean, while the smaller ones remained behind. 



The next collection to be considered was made in the Columbia River near the mouth 

 of the Little White Salmon River, about 50 miles above the point where the Willamette 

 River joins the Columbia. This collection was made May 25, 1916, at which time 24 fry 

 and I yearling were captured. The fry average 44.6 mm. in length and range from 

 37 to 61 mm. The mode is at 49 mm. Six specimens have no scales, 7 have only 

 platelets, and 11 have scales with rings. Males and females are present in this col- 

 lection in equal numbers and are also of equal size, both sexes averaging 44.6 mm. in 

 length. The following table (7) contains the data: 



Table 7. — Fry from Columbia Rtver near Mouth of Little White Salmon River, May 25. 1916. 



