PROGRESS IN BIOLOGICAL INQUIRIES, 193 2 105 



determinino: the age composition of the run, which numbered approxi- 

 mately 1,500,000. Ten groups, consisting of fish of different ages 

 and which had spent varying periods in fresh water before migrating 

 to sea, were present. These were returns from 4 brood years, namely : 

 1925, 1926, 1927, and 1928. The majority of the run was produced 

 by the brood years of 1926 and 1927, the former furnishing 589,000 

 fish and the latter 790,000. At the present time complete data are 

 at hand as to the total return of fish from the brood years of 1921 to 

 1925, inclusive, but more data are necessary before any definite con- 

 clusions can be made as to the necessary magnitude of an adequate 

 spawning reserve. 



The marking experiments were continued, 59,000 seaward migrants 

 being marked and liberated. In previous years the same mark or 

 marks have been used throughout a season's marking. This year four 

 marks were used: First, the amputation of the right ventral and 

 adipose fins; second, the right pectoral and adipose; third, the left 

 ventral and adipose; and fourth, the left pectoral and adipose. Thus 

 the marking was divided into four separate experiments. Fifteen 

 thousand seaward migrants were marked in each experiment except 

 the fourth. Only 14,000 were used for the fourth experiment as the 

 migration ended and it was impossible to obtain more. The marking 

 was carried on from May 27 until June 22. It has been noted that 

 the age composition of a migration changes from day to day during the 

 migration, also the size frequency distribution of all age groups 

 decreases as the migration proceeds, and the purpose of this added 

 feature of the marking experiment is to determine whether or not 

 the migrants which appear early in the migration also appear early 

 in the season when they return as adults. These experiments will 

 also determine whether or not a differential mortality exists between 

 the large and small individuals of the same age group during their 

 stay in the ocean. 



The main purpose of the marking experiments is to determine the 

 mortality of the fish during their stay in the ocean. By marking a 

 given number of seaward migrants and then sampling the run during 

 the j^ears when they are returning the total number of marked fish 

 returning may be calculated. Knowing the number of fish marked 

 and the number returning, the mortality rate in the ocean can be 

 determined. The problem is shghtly compHcated due to the fact that 

 the fish from a given seaward migration remain in the ocean for vary- 

 ing periods of time ranging from 1 to 3 years. It is necessary, there- 

 fore, to sample the run during the three years following a marking 

 experiment to determine the total return from that experiment. 

 During the past season 159,279 Karluk red salmon were carefully 

 examined and 1,215 marked fish were recovered of which 13 were from 

 the marking of 1931; 1,090 were from the marking of 1930, and 112 

 were from the marking of 1929. 



Knowing the mortality of the fish in the ocean, the number of sea- 

 ward migrants resulting from a given spawning can be calculated, 

 and as the number of fish in each spawning escapement is ascertained 

 by means of a counting weir which is operated in the river the ratio 

 of the number of seaward migrants to the number of fish in the 

 escapement from which they were derived can be calculated. There 

 is reason to beheve that fluctuations in this ratio from year to year 

 are to a large extent responsible for the fluctuations in the size of the 



