556 



FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



Table 9. — Contents of stickleback stomachs, Karluk Lake 

 [Numbers in parentheses are range of number of organisms per stomach] 



Table 10. — Contents of stickleback stomachs from fish of 

 three size groups, Karluk Lake, July 7, 19,' f 9 



Ostracods and rotifers were present. Several 

 stomachs contained pea clams, sometimes in large 

 enough numbers to constitute considerable bulk. 

 Other food items, encountered only occasionally, 

 included snails, leaches, planarians, and water 

 mites. Vegetation or phytoplankton, in identi- 

 fiable form, was never or scarcely ever present. 



Several stomachs contained fish eggs, easily 

 identifiable as stickleback eggs. No other fish 

 material was found. 



Some changes in the feeding habits through- 

 out the summer may be noticed (tables 8 and 9). 

 Chironomids were fewer in the stomachs in the 

 latter part of the season. Various plankton in- 

 vertebrate species fluctuated in numbers in the 

 stickleback diet, probably in relation to fluctua- 

 tions of numbers of these species present in the 

 water. 



There are also differences in the food selected 

 by fish of various size groups (table 10). Fewer 

 of the large fish were feeding on Cladocera. more 

 of them on ostracods. Stickleback eggs were 

 found in only the larger fish. Possibly the eggs 



are too large to be swallowed by the small fish. 

 Or perhaps the larger fish were in a nesting area 

 and thus had ready access to eggs. 



Role as Prey 



Several species of fish present in Karluk and 

 Bare Lakes may be predators on the stickleback. 

 The arctic charr {Salvelinus alpinus), which does 

 not occur in Bare Lake, is a year-round resident 

 in Karluk Lake in substantial numbers. Accord- 

 ing to Morton 5 and DeLacy 6 , this charr feeds 

 on sticklebacks and stickleback eggs, especially hi 

 the months of June and July. In the study of 

 the food habits of the arctic charr, in the Wood 

 River drainage in western Alaska, it was found 

 that the charr consumed large numbers of stickle- 

 backs, particularly when young red salmon were 

 not readily available. 



The Dolly Varden charr (Salvelinus malma) is 

 said by Morton not to utilize sticklebacks in Kar- 

 luk Lake. Of 60 stomachs of Dolly Varden taken 

 in Bare Lake in the period June— August 1956, 

 only 3 contained stickleback. It is likely that 

 sticklebacks are eaten to some extent by the 

 fingerling coho salmon and the rainbow trout, 

 especially during the winter, when food items 

 such as insects are not available in large numbers. 

 Baxter (1956) found the stickleback to be an 

 important item in the diet of the rainbow trout 

 in a lake near Anchorage, Alaska. Also, the 



5 See footnote 2, p. 543. 



6 Contributions to the life histories of two Alaskan charrs. 

 Salvelintta malma iWalbaitm) and Salvelinus alpinus (Linnaeus). 

 By Allan Clark DeLacy. Doctoral thesis. University of Wash- 

 ington, Seattle. (Typewritten) 114 pp., 1941. 



