250 



SALMON OF THE KARLTTK RIVER, ALASKA 



ber 17, inclusive, a period of 27 days. It was replaced on September 18, and counting 

 was continued until the end of the season. Unfortunately, fishing for that season 

 stopped on August 18, and catch data are not available from which to judge the rela- 

 tive abundance of fish in the run. Data on the trend of abundance of the various age 

 groups in the run up to August 18 have been examined and compared with data for 

 previous years, and from this analysis it is estimated that the escapement during the 

 period was approximately 300,000 red salmon. The counted escapement during the 

 period the weir was in operation was 846,299. 



The weir is located approximately 4 miles from the mouth of the river and in this 

 4-mile stretch the river widens out to form a lagoon, the lower end of which is usually 

 slightly brackish. The fish, after entering the mouth of the river, stay in this lagoon for 

 a varying period of time, averaging about 1 week, before they proceed up the river 

 through the weir. Consequently, in calculating the age-group composition of the 

 escapement, the percentages of the various age groups in one 7-day period, as deter- 

 mined by an analysis of the scale samples, (tables 3 to 16) were applied to the escape- 

 ment of the following 7-day period. 



The percentage occurences of the various age groups in the spring, fall, and total 

 escapements for the years 1922 and 1924 to 1936, inclusive, are presented in table 18. 

 There was a considerable fluctuation in the percentage occurrence of the principal 

 age groups in the escapement from year to year. The percentage of the three prin- 

 cipal age groups in the total escapements ranged from 24.1 to 81.1 for the 5 3 group; 

 4.0 to 38.6 for the 6 4 group; and from 4.5 to 32. S for the 6 3 group. 



This variation in the age composition of the escapements was due mainly to the 

 fact that each year's escapement is composed of returns from several brood years. 

 For example, a single escapement may be composed of 5-year fish from a brood year 

 producing a small run, together with 6-year fish from a brood year producing a large 

 run. In this instance the percentage of 5-year fish would be below average, and the 

 percentage of 6-year fish would be above average. However, if the 5-year fish were 

 from a very productive brood year and the 6-year fish were from a less productive 

 brood year, the results would be just the reverse. 



Table 18. — Percentage occurrence of the various age groups in the spring, fall, and total escapements of 



1922, and of 1924 to 1936, inclusive 



