KARLUK RIVER RED-SALMON INVESTIGATION 



55 



Careful examination of the sizes attained by the principal age groups in different 

 years may yield data of interest and importance. How slight the differences are 

 from year to year within the limits of the same age group is not generally appre= 

 ciated. Years are cited in which the fish are said to average very large, as well as 

 other years in which the reverse condition appears; but invariably, when such is the 

 case, an examination of the runs demonstrates that the fish run small in years when 

 a younger age group dominates, and average large when an older and larger group 

 prevails. 



If the groups are segregated, however, and their average lengths and weights 

 carefully ascertained, the conviction is quickly formed that we are dealing with a 

 highly standardized race characteristic. From year to year the same group presents 

 average sizes that differ by very small amounts. Usually, however, when the data 

 have been gathered by the same observer, it will be found that the lengths of males 

 and females in the same year vary from the norm in the same direction, and can be 

 checked by parallel differences in the weights. In such cases, where the sampling 

 has been adequate, the differences between one year and the next, however small 

 these may be, are genuine phenomena and in need of explanation. 



The dominant 5 3 group of the Karluk run offers abundant material for such 

 investigations; but the data at present available are not adequate. For the early 

 years here reported on we have only limited samples covering only a few days of the 

 runs. Furthermore, the measurements were made by different observers, who 

 had little or no training. However, we shall give a list of the average lengths 

 (Table 20) thus ascertained for the 5 3 group in different years, for such information 

 as, under the circumstances, it can be expected to furnish concerning the extremes 

 of variation to which these average lengths are subject. 



Table 20. — Average lengths, in centimeters, of males and females of the 5} group in a series of years 



Year 



Males 



Females 



Year 



Males 



Females 



1916 



63.0 

 63.5 

 64.5 

 64.4 

 60.9 



59.3 

 61.0 

 60.3 

 60.3 

 58.4 



1924.. 



62.7 

 62.9 

 63.5 



59.1 

 59.9 

 61.1 



1917 



1925. 



1919 



1926- - 



1921. 



General average 



1922 



63.2 



59.9 







The only considerable variation from the general average is found in the year 

 1922, which is noted as having had the poorest run in the history of the Karluk River. 

 Apart from the record of that year, the extremes of variation are only 1.8 centimeters 

 in the case of males and 2 centimeters in the case of the females. With regard to 

 the abnormally small sizes shown for the year 1922, the question arises whether 

 there is any direct connection between the failure of the run of that year and the 

 small size of the fish. Was there a scarcity, during the growth of this brood, in 

 the pelagic organisms on which the red salmon almost exclusively feeds, a scarcity 

 that caused extensive mortality among the colony and stunted the growth of those 

 that survived? A reliable series of measurements, extended over a term of years, 

 may throw light on this important question. 



The average lengths and weights of the 5 3 group during each of the days in 

 1926 on which we secured samples are given in Table 21. 



