FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 289 



seaward migrants, undoubtedly, were marked but their numbers probably were so 

 few that they were not represented in the samples of fish from which scales were taken 

 for age determination. 



From the results of these experiments it appears that there was a differential 

 mortality between the fish marked by excising the adipose and one ventral fin, and 

 those marked by excising the adipose and one pectoral fin. The average survival from 

 the first and second experiments was 18.4 percent, and the average survival from the 

 last two experiments was also 18.4 percent. However, the average survival from the 

 first and third experiments was 20.5, while the average survival from the second and 

 fourth experiments was only 16.2 percent. Hence, there was only 79.2 percent as 

 good a return from the fish marked by removing the adipose and one pectoral fin as 

 there was from the fish marked by removing the adipose and one ventral fin. These 

 results agree closely with those obtained in the 1930 experiment in which the total 

 return from the the fish marked by amputing the adipose and one ventral fin was 21.0 

 percent, and the total return from the fish marked by amputating the adipose and one 

 pectoral fin was 17.4 percent. In the 1930 experiments, there was only 89.2 percent 

 as good a survival of fish marked by excising the adipose and one pectoral fin as there 

 was of fish marked by removing the adipose and one ventral fin. 



The percentage occurrence of marked fish of a single age and one type of mark 

 remained fairly constant throughout the seasons in which they were sampled. How- 

 ever, from the marking of 3-year seaward migrants, the ratio between the return of 

 two-ocean fish and the return of three-ocean fish was 2.38 to 1, 1.25 to 1, 1.37 to 1, 

 and 0.62 to 1 for the first, second, third, and fourth experiments, respectively. Thus, 

 of the 3-year seaward migrants the early migrating fish spent, on the average, a shorter 

 time in the ocean than the late migrating fish. From the marking of 4-year seaward 

 migrants, the ratio between the return of two-ocean fish and the return of three-ocean 

 fish was 2.94 to 1, 1.64 to 1, 1.95 to 1, and 1.5 to 1 for thefirst, second, third, and fourth 

 experiments, respectively. The returns from the marking of 4-year seaward migrants 

 and the returns from the marking of 3-year seaward migrants both demonstrated a 

 positive correlation between the time of occurrence during the migration period, and 

 the length of time spent in the ocean. 



As there appears to be a differential mortality between fish marked by removal of 

 the adipose and one ventral fin, and fish marked by removal of the adipose and one 

 pectoral fin, in comparing the results of the 1932 experiments with experiments of 

 other years, it seems advisable to consider only the two experiments in which the fish 

 were marked by the amputation of the adipose and one ventral fin. Grouping the 

 data of the first and third experiments, 30,000 migrants were marked, 705 fish were 

 recovered, and 6,142 marked fish returned (20.5 percent). The returns from the marked 

 3-, 4-, and 5-year seaward migrants were 21.9, 19.1, and 2.3 percent, respectively, giving 

 evidence for the first time contrary to the hypothesis that there is no positive correla- 

 tion between age at time of migration, and survival. 



EXPERIMENTS IN 1933 



In 1933 (table 43) 40,000 seward migrants were marked by the amputation oi the 

 adipose and both ventral fins, 959 fish were recovered, and a calculated total of 8,212 

 marked fish returned (20.5 percent of the number marked). The return from the 

 2-, 3-. 4-, and 5-year marked seaward migrants was 18.8, 18.3, 24.9, and 15.6 percent, 

 respectively. 



