236 



BULLETIN OF THE BtTREAU OF FISHERIES 



Table 16. — Chinook salmon tnarked at Bonneville hatchery during the fall of 1U20, xohen approxi- 

 mately 13 months old, and recovered during the seasons of 1923, 192%, and 1925 



The consistency with which these fish entered fresh water during the early part 

 of the season greatly outweighs the few doubtful cases in other experiments in show- 

 ing that the time at which the adults enter fresh water is determined by heredity 

 and is not affected by early environment. The parents of the fish marked in this 

 experiment were of the early spring run that spawns in the headwaters of the Wil- 

 lamette River. The fingerlings marked were reared at Tanner Creek, where only 

 salmon of the fall run are found normally; but the time when the adult marked fish 

 returned to fresh water to spawn was not altered by this change in their early life. 

 This is shown most clearly by the records of the 1924 recoveries. (See Table 13.) 

 Of the 208 recoveries for which the date of capture is known, 82 per cent were taken 

 during the first two weeks after the season opened on May 1. The largest catches 

 were made during the first four days of the season. The date of the latest recovery 

 from this experiment was June 13. 



The evidence from this experiment, regarding the factors that influence the 

 adult salmon to return to a particular tributary to spawn, is in complete agreement 

 with that derived from experiment No. 6. As in experiment No. 6, none returned to 

 the tributaries in which the eggs were taken. Approximately one-half of the 

 reported recaptures were made in the Columbia several miles above the mouth of 

 Tanner Creek, where the fingerlings were liberated, whereas only three ran into 

 Tanner Creek. From these facts it is evident that heredity has no effect on the 

 tendency in question and that early environment is an influencing but by no means 

 controlling factor. 



Scales from all of the recaptured adult fish were examined microscopically in 

 the usual manner. Evidence of absorption, which normally sets in soon after the 

 fish enter fresh water, was found in nearly aU cases. In the majority the original 

 margin was removed entirely, but there remained at least a part of the last winter 

 band, which in fish that leave the ocean in the spring Hes just within the margin of 

 the complete scale. In a few of the 5-year-olds and most of the 6-year-olds the last 

 winter band was entirely lacking, but a wide band of well-spaced rings following the 

 preceding winter check is ample assurance that the fish were in their fifth and sixth 

 years, respectively. Typical scales from fish recovered during their third, fourth, 

 fifth, and sixth years are shown in Figures 41, 42, 43, and 4.5. 



The nuclei of the scales of 50 of the 5-year-olds and of all of the other age groups 

 were measured for comparison with the scales of the fingerlings. Ail were distinctly 

 of the stream type. The range of variation in size and number of rings was shown 

 most clearly by the measurements of the 50 unselected 5-year-olds, which are tabu- 



