242 



SALMON OF THE KARLUK RIVER, ALASKA 



on the day of capture. Each scale sample contains scales from about 100 fish, these 

 fish being taken at random from the day's catch. The scales are cleaned, mounted 

 in sodium silicate between glass slides, examined under a microscope, and the age of 

 the fish in the sample determined. 



A preliminary study of the age-group composition of the various samples showed 

 that the composition of the run changes throughout a season, and consequently it 

 was found advisable to divide the season into a series of short successive periods of 

 time. For the purpose of comparison these units of time should begin and end on the 

 same dates each year, and so the scale samples, escapements, and runs have been 

 grouped in 7-day periods which coincide from year to year. 



Tables 3 to 16 give the age-group analyses of the several weekly samples taken in 

 1922, and in the years 1924 to 1936, inclusive. It will be seen from these tables that 

 the age-group composition of the run changes considerably during the season, and 

 also that the percentage occurrence of any one age group varies from year to year. 



In considering the three principal age groups, 5 3 , 6 3 , and 6 4 , it will be noted that 

 5 3 usually is the dominant age group present in the run. The percentage occurrence 

 of the 6 3 age group always decreases as the season progresses, this age group never 

 being important toward the end of the run. The percentage occurrence of the 6 4 age 

 group generally increases as the season progresses. This age group, while seldom of 

 importance in the early part of the season, usually is quite important in the latter 

 part of the season. 



The data included in tables 3 to 16 are of further value in that they are essential 

 in calculating the percentage occurrence of the various age groups in the yearly 

 escapements and in the returns from these escapements as given in tables 18 and 25, 

 respectively. Since the salmon returning to Karluk each year from each of the 

 previous spawning populations, or escapements, can be segregated according to age, 

 the data in tables 3 to 16 are likewise essential in calculating the returns from known 

 escapements. These returns are given in table 20. 



Table 3. — Percentage occurrence of each age group, during week, in the Karluk red-salmon run of 

 1922, determined by analyses of scale samples collected from a total of 2,469 fish 



