290 



SALMON OF THE KARLTJK. RIVER, ALASKA 

 Table 43. — Data for the 1933 marking experiment 



DISCUSSION OF MARKING EXPERIMENTS 



In comparing results of the several years marking experiments, it seems advisable 

 to consider the returns from only those experiments in which the fish were marked by 

 the amputation of the adipose and one, or both, ventral fins. It also seems advisable 

 to combine the results in those years when duplicate experiments were run. 



In those experiments in which the adipose and one, or both, of the ventral fins were 

 amputated, the returns from the experiments of the years 1926, and 1929 to 1933, 

 inclusive, are 20.8 (incomplete), 22.3, 21.0, 23.6, 20.5 and 20.5 percent, respec- 

 tively. These results are remarkably uniform and indicate that the survival rate 

 of the fish, during their stay in the ocean, has been quite constant. 



Grouping the data of all experiments wherein the fish were marked by the ampu- 

 tation of the adipose and left, right, or both ventral fins gives a total of 169,836 

 three-fresh-water fish marked and a calculated return of 29,560 marked fish, or a 

 17.4 ll percent return. For the four-fresh-water fish it is found that 93,944 were 

 marked, and 24,142 marked fish returned, or a 25.7 percent return. 



While combining the data in this manner may be subject to some criticism, it is 

 quite evident that a differential mortahty exists between the three-fresh-water fish 

 and the older and larger four-fresh-water fish. The greater survival of the four-fresh- 

 water fish during their stay in the ocean would seem to indicate that a longer lake 

 residence was advantageous. However, this greater ocean survival may be drastically 

 over-balanced by the mortality during the extra year spent in fresh water. 



The percentage occurrence of marked fish in the different age groups examined 

 varied considerably, and whde a certain amount of the variation is due to random 

 errors in sampling, it cannot all be ascribed to that factor. The age-group com- 

 position of the seaward migration changes considerably during the migration period, 

 and as there is no means of determining, actually or relatively, how many migrants 

 pass downstream each day, it is impossible to mark a constant proportion of the 

 migration. 



" Does not include the three-ocean fish from the experiments of 1926. 

 the results. 



However, this omission would not materially affect 



