FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 241 



It is evident from the statistical study of the catches of Karluk Eiver red salmon 

 and also from the analysis of the scale samples that the majority of the fish compris- 

 ing the runs dming the early years of the fishery were 5 years of age on attaining 

 maturity. Therefore, the annual catches have been divided into five groups and the 

 data are presented in figure 1. This method of presenting the data gives a clearer 

 indication of the trend of catches from one cycle-year to another, as the catch of a 

 particular year can be easily compared with the catch during a year 5 years previous 

 to, or 5 years following that year. While these data represent the catches of red 

 salmon, not the size of the runs for the various years, the nature of the fishing opera- 

 tions at Karluk from 1S95 to 1921 was such that the fishing effort was fairly constant 

 from year to year; hence the catches, in«, measure, depict the relative size of the runs. 

 The trend for each of the 5 cycles has been downward since the beginning of intensive 

 fishing, and although such a condition might be due to a long period of unfavorable 

 environmental conditions, it seems probably that overfishing must be largely 



responsible. 



AGE AT MATURITY 



One of the major problems involved in the study of the Karluk River red salmon 

 is the determination of the approximate number of fish derived from each spawning 

 population. This necessarily involves the determination of the approximate number 

 of fish of each age group 6 found each year, but such a determination is by no means 

 a simple matter. Karluk red salmon vary from 3 to 8 years in age, and the percentage 

 occurrence of the various age groups changes throughout the season. 



In addition to the wide spread in time of maturity of the Karluk River red salmon 

 there is a further complication, in that fish of a given age have different combinations 

 of fresh-water and ocean histories. Thus of the fish maturing in their fifth year, some 

 migrate to the ocean in their second year, some in the third year, some in their fourth 

 year, and some in their fifth year. These four groups of fish, with different fresh-water 

 histories, may stay in the ocean 3, 2, 1, and years (a few months), respectively, and 

 all return in the fifth year as mature fish. This diversity in fresh-water and ocean 

 history also occurs in the fish of other ages, so that 20 different age groups have been 

 found in the samples collected for age determination, the complete list being as follows: 

 3i, 3 2 , 3 3 , 4i, 4 2 , 4 3 , 4 4 , 5 2 , 5 3 , 5 4 , 5 5 , 6 2 , 6 3 , 6 4 , 6 5 , 7 3 , 7 4 , 7 5 , 8 4 , and 8 6 . 



The age of a fish may be determined with substantial accuracy by an examination 

 of some of its scales under a microscope, but it is impossible to examine scales from 

 every fish in the run. Recourse must be had to a process of sampling so that by the 

 examination of the scales of a few thousand fish the age-group composition of the 

 escapement and commercial catch can be calculated. Samples of scales are obtained 

 for this purpose several times a week during each season from the fish caught in the 

 seine fishery near the mouth of the river. It is fairly certain that the fish so caught 

 are representative of the population of fish congregated near the mouth of the river 



• The method, first used by Gilbert and Rich (192?), for designating the age of salmon is as follows: A fish resulting from an egg 

 laid in the spawning gravels in 1930 and which migrated to the ocean in 1933 and returned to the river in 1935 is called a "five-three" 

 and designated thus "83". Such a fish would have emerged from the gravels of the spawning beds in the spring of 1931 and would 

 have spent two growing seasons, i. e„ the summers of 1931 and 1932. in fresh water. In referring to its fresh-water history it is called 

 a "three-fresh-water fish" because it migrated seaward in its third year. It would have spent two full growing seasons, i. e., 1933 

 and 1934, and part of a third year in the ocean; but in referring to its ocean history it is called a "two-ocean fish," because it returned 

 as an adult in the second year following its seaward migration. A fish which migrated to the ocean in its fourth year and which 

 returned in its sixth year is called a "six-four" and designated thus "6V\ 



