THREESPINE STICKLEBACK OF KODIAK ISLAND 



549 



June July Aug Sept 

 First Summer 



June July Aug Sept 

 Second Summer 



June July Aug Sept 

 Third Summer 



Figure 8. — Growth of Bart- Lake sticklebacks. Kach curve represents a year class. 



modes of length-frequency histograms. 



Points on curves derived from 



sents a fish whose age was determined by otolith 

 reading. 



In these symbols, the sexes are separated for 

 the fish in their third summer (2 years old). 

 The females attain a somewhat larger size than 

 the males. 



The fact that the curve, which presumably in- 

 dicates average sizes, does not pass through the 

 median of the lengths indicated by the otolith 

 readings may be due to an unconscious tendency 

 on t lie part of the technician to select usually the 

 larger fish in a given size-group for otolith 

 samples. 



In a similar diagram for the Karluk Lake 

 sticklebacks (fig. 10), the symbols represent mean 



lengths of fish of length-frequency modes (for 

 samples through the summers of 1948 and 1949), 

 and the curve indicates the regression line as 

 drawn by visual inspection. The vertical bars 

 show the ranges of lengths of fish the ages of 

 which were determined by otolith reading. Sam- 

 ples for otolith determinations were available 

 only for dates in mid-July (1956). 



As shown in figures 8-10, the Karluk Lake and 

 Bare Lake sticklebacks do most of their growing 

 from June 1 to September 1 and make compara- 

 tively little growth through the fall, winter, and 

 spring. 



The sticklebacks in Bare Lake average from 

 32 to 35 mm. in standard length at the end of 



Fku'RE i). — Growth of Bare Lake sticklebacks. Curve is composite of growth of 3-year classes (from figure 8). 

 Scattered points represent ages and lengths of individual fish determined by otolith reading. 



