544 



FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



to Karluk Lake, presumably fish in spawning 

 migration. 



The degree of fluctuation of numbers from 

 year to year is not known. Certain beach loca- 

 tions in Bare Lake were seined several times each 

 summer in the years 1951—55. The catches varied 

 widely, from less than 50 to more than 4,000 

 (table 6). No attempt has been made to make 

 a statistical analysis of the variance or to arrive 

 at a measure of its significance; since many ex- 

 ternal factors, such as light and wave action, are 

 involved. Assuming that these factors averaged 

 out to some extent, there is indication that a 

 population peak was reached in 1953. 



The proportionate strength of the different 

 year classes cannot be estimated, since seine hauls 

 may not constitute random samples of the popu- 

 lation. 



Table 6. — Seine hauls, southwest corner Bare Lake, and 

 catch of sticklebacks per haul 



Date 



1951 



July 8... 

 July 22.- 

 Aug. 25.. 

 Sept. 12.. 



June 25.. 

 July S.- 

 July 29.. 

 Sept. 11.. 



1953 



May 23..-. 



June 8 



June 27 



July 24.... 

 Aug. 12 ... 

 Auk. 26—. 



1954 



May 23.. 

 June 7— 

 June 24 . 

 June 26.. 

 July 12.. 

 July 26.. 

 July 29.. 

 Aug. 7 -. 

 Aug. 10-. 

 Aug. 17.. 

 Aug. 27.. 

 Sept. 28.. 



Catch l 



1.000 

 350 

 400 

 150 



1,000 



100 



50 



50 



150 



1,700 



4,300 



1.400 



250 



150 



850 

 950 

 300 

 800 

 650 

 50 



250 

 250 



Average 

 for year 



Date 



May 23 

 June 7... 

 June 24.. 

 July 12.. 

 July 18.. 

 July 30.- 

 Aug. 10 

 Aug. 17. 

 Aug. 27. 

 Sept. 6.. 



May 30. 

 June 20. 

 July 10.. 

 July 23.. 

 Aug. 4 

 Aug. 28 



Catch ' 



1.300 

 400 

 600 

 700 

 250 



100 



150 



1.300 



250 

 500 

 4110 

 250 

 200 

 150 



A verage 

 for year 



1 Figures rounded to nearest 50. 



2 Dash indicates fewer than 25. 



Habitat 



Essentially, the stickleback in Bare and Karluk 

 Lakes is an inhabitant of the shallow waters. A 

 few fish, but no large numbers, have been ob- 

 served on the surface of Karluk Lake at a con- 



siderable distance from the shore. Morton 

 caught 12 sticklebacks in one set of a fyke net 

 at a depth of 80 feet in Karluk Lake, but did not 

 take any sticklebacks in a set at 200 feet. Simi- 

 larly, C. E. Walker (private communication) re- 

 ports having taken sticklebacks in Karluk Lake 

 in a fyke net set at a depth of 30 feet but not 

 in a net set at 126 feet. 



Presumably, food is more readily obtainable 

 along the shoals; although plankton animals, 

 which comprise a substantial part of the stickle- 

 back diet, are plentiful in at least the upper 

 layers of the water in the center of the lake. 

 It is probable, also, that conditions of light, tem- 

 perature, and shelter are not as suitable to the 

 stickleback in the lower levels as in the surface 

 water. Bigelow and Schroeder (1953, p. 309) 

 state that Gasterosteus aculeatus in the North 

 Atlantic Ocean often is picked up far from land, 

 but nearly always on the surface, usually in 

 patches of weeds. 



There is little aquatic vegetation on the shoals 

 of Karluk and Bare Lakes. Often, when dis- 

 turbed, the sticklebacks dart to the bottom to 

 hide among rocks and moss. Much of the time 

 they stay in open water and depend for protec- 

 tion on their appearance and behavior. Weeds, 

 where present, furnish feeding opportunity in 

 the way of insect larvae and small Crustacea 

 and Mollusca attached to the plants. 



Age, Size, and Growth 



In the published literature to date, the most 

 comprehensive work on age determination in 

 sticklebacks, which has come to our attention, is 

 that of Jones and Hynes (1950). These authors 

 determined age by means of the otoliths and drew 

 up growth-rate tables and curves for three spe- 

 cies of sticklebacks from the Birket River in 

 England. 



We have examined otoliths of about 250 stickle- 

 backs from Bare Lake and Karluk Lake. Also, 

 we have drawn up length-frequency histograms 

 for about 65 samples as described below. The 

 information obtained by the two methods is in 

 good agreement and provides a reasonably reli- 

 able estimate of age and growth. 



In preparing and examining the stickleback 

 otoliths, we have followed essentially the tech- 

 nique used by Jones and Hynes. Only fresh fish. 



