SEAWARD MIGRATION OF CHINOOK SALMON. 7 



way as ordinary films and positive prints produced. The prints included with this 

 report were made in this manner. A Leitz photomicrographic apparatus fitted with 

 a 24-mm. mikro-summar was used and a small Bausch & Lomb arc lamp with condens- 

 ing lens as a source of light. For the magnification used, 35 diameters, Azo, F, hard 

 X requires an exposure of about 90 seconds and contrast Cyco about 15 seconds. The 

 paper is placed in the regular plate holder behind a piece of clear glass. Another piece 

 of glass or of stiff cardboard is placed behind the paper in order to hold it flat. The 

 best focus is one which makes each line of the scale appear on the ground glass as a 

 bright line having a narrow black line in the center. Considerable experience is nec- 

 essary before one can obtain this focus property. The size of the arc light will deter- 

 mine the amount of time required for a proper exposure, and the same size of arc should 

 be used, therefore, for all photographs in a series. The printing requires an exposure 

 to bright daylight (not sunlight) of about five seconds. 



PRESENTATION OF DATA. 



FISH FROM THE COLUMBIA RIVER. 



The earliest collections made during any year were taken in the latter part of 

 March and eariy in April, 1916. At this time a trip was made by launch from Portland 

 to Astoria. Frequent hauls were made at different points, but many were unsuccessful 

 because of the flood stage of the river. Also poor acquaintance with the river made it 

 impossible to select the most favorable spots for seining. A seine 100 feet in length 

 was used. This had half-inch mesh in the wings and one-fourth inch mesh in the bag 

 The smallest salmon fry could be collected with this gear, as is proved by the fact that 

 fry which had not completely absorbed the yolk sac were frequently captured. The 

 later trips were more successful than the earlier ones, since the favorable places for 

 seining had been learned and attention confined to these. 



Collections were made March 31, 1916, at Mayger, Oreg., and at Grims Island, near 

 Clatskanie, Oreg. On April i and 2 several collections were made at different points in 

 the lower part of the Columbia estuary. The best collections were obtained on Sand 

 Island and near Point Ellice, Wash. One hundred and forty-nine specimens in all were 

 taken. Forty-seven of these were yearlings and 102 were fry. The study of the 

 yearlings will have greater significance if delayed until after the development of the 

 fry during the first year shall have been followed. The collections of fry made on this 

 trip have all been studied separately, but no significant variations appeared, and the 

 data are therefore presented in a single table (i). 



Less than one-half of the fry had developed sufficiently to fonn even the central 

 nuclear plates of the scales. Gilbert (1913a) describes a similar condition in the case 

 of the migrating fry of the sockeye. Twenty-three individuals show the central plate- 

 lets only and 19 have scales well enough developed for rings to be present. The aver- 

 age length" is 38.7 mm., with the mode at 38 mm. The average number of rings on the 

 scales of the 19 specimens possessing scales sufficiently developed to show rings is 1.7. 

 The average length of the anterior radius of the scales is 6.3 on the arbitrary scale. (See 

 p. 6.) The following table (i) gives all the data regarding these collections. 



*» The averages employed iu this paper are invariably Uie weighted mean. 



