FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



277 



Thus there is a decrease in the percentage of males, and conversely an increase 

 in the percentage of females, with increased length of time spent in the ocean. The 

 males tend to mature after a shorter period of ocean residence than the females, and 

 this precocious development of the males also is apparent from a consideration of the 

 total age of the mature fish. In a group of the same ocean history, with the exception 

 of the three-ocean fish, the younger fish are more predominately male than the older 

 members of that group. 



The percentages of males and females returning from the seaward migrations of 

 1923 to 1933, inclusive, are presented in table 30. These percentages were determined 

 by calculating the number of males and females of various ocean histories returning 

 from a single seaward migration and then adding the several groups together to 

 obtain the total number of males and females returning from that migration. The 

 percentage of males varied from 40.1 to 48.8 percent and the percentage of females 

 from 51.2 to 59.9 percent, and the average for all years was 43.9 percent males and 

 56.1 percent females. 



Table 30. — Percentage of males and females in the returns from the seaward migrations of 1923 to 19S3 



The sex ratio of these fish changes from approximately 50 percent males and 50 

 percent females at the time of seaward migration to approximately 44 percent males 

 and 56 percent females on their return from the ocean. Since the males, on the 

 average, spend less time in the ocean than the females, the mortality of the males 

 should be less than that of the females, which should result in a preponderance of 

 males. A part of the Karluk run is intercepted by a gill-net fishery to the north and 

 east of the Karluk River, and because of the size of the gill-net mesh employed, a great 

 percentage of the larger fish in the run is captured. As the average size of the males is 

 slightly greater than the average size of the females, more males than females are 

 captured and thus the percentage of males in the fish arriving at the Karluk River, 

 where the data for table 30 were obtained, is reduced. It is not considered that the 

 selective action by the gill nets accounts entirely for the discrepancy in the sex ratio 

 because the gill-net catches are fairly small in relation to the size of the run as a whole. 

 A differential mortality in favor of the females during the time spent in the ocean does 

 not appear probable. A satisfactory explanation of this phenomenon is lacking at the 

 present time. 



MARKING EXPERIMENTS 



A series of marking experiments was begun at Karluk River, Alaska, in 1926.' 

 In these experiments, red salmon migrating seaward were marked by the removal of 



• These marking experiments were initiated by the late Dr. C. H. Gilbert, and Dr. W. H. Rich, both of the former United 

 States Bureau of Fisheries. 



