546 



FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



Figure 5. — Stickleback otoliths: Top, otolith from fish 

 age 2-3 months; Middle, otolith from 1-year-old fish; 

 Bottom, otolith from 2-year-old fish. 



1 year old, taken in June, would show in order: 

 centrum, first transparent ring, first opaque ring, 

 and, at the outer edge, the beginning of the 

 second transparent ring. The same fish, if cap- 

 tured in September of the same year, would have 



two transparent rings, and the second opaque 

 ring would be forming at the edge. Shown in 

 figure 5 are photographs of otoliths taken from 

 fish of a few months, 1 year, and 2 years of age. 



As mentioned by Jones and Hynes, the times 

 of formation of the light and dark rings in the 

 otolith are not the same for all species of fish. 

 In certain fishes, such as Clupea harengus, the 

 transparent ring appears to be formed in winter 

 and the opaque ring in the summer, the reverse 

 of Gasterosteus. 



Our samples for length-frequency determina- 

 tion were taken by seining, which is probably 

 more nearly nonselective as to size than any other 

 method available to us. However, it may be that 

 a completely random sample of the population 

 cannot be obtained, since the sticklebacks may 

 sort and distribute themselves by size to some 

 extent. It is believed though that size selectivity 

 in the sampling is more or less smoothed out by 

 the large number of samplings. 



Samples in Bare Lake were taken at intervals 

 of 1 to 2 weeks during the summers (approxi- 

 mately June 1 to September 1) of 1950-56, in- 

 clusive, and in Karluk Lake during the summers 

 of 1948 and 1949. In Bare Lake almost all of 

 the sampling was done in one area, the beach at 

 the southwest corner of the lake. In Karluk 

 Lake most of the samples were taken around or 

 near Camp Island on the east side of the lake. 



Each sample consisted of from 100 to 400 fish. 

 Standard length of each fish was measured in 

 millimeters. A length -frequency histogram was 

 drawn for each sample expressed in percentage 

 of the total number of fish in the sample. For 

 the Bare Lake samples, the lengths were grouped 

 in 2-mm. intervals; for the samples from Karluk 

 Lake, in 3-mm. intervals. The histograms show- 

 ing the sequence of samples from Bare Lake for 

 one summer (1954) are presented in figure 6. In 

 figure 7 the sequence for Karluk Lake in the 

 summer of 1949 is shown. 



Standard lengths may be converted to fork 

 lengths or total lengths (all of these terms are 

 well defined in recent literature) by use of the 

 following factors: F. L./S. L.=1.17, and T. L./ 

 S. L.=1.21. 



Jones and Hynes (op. cit.) give a summary of 

 the information regarding age and size of the 

 threespine stickleback. Various authors have 



