Cabin, Celestine and Caledonia lakes, Jasper National Park, contain naturally reproducing populations of rainbow trout (Oncorhynchus mykiss) and lake chub (Couesius plumbeus), but whether these populations are native was not known. I used subfossil Chaoborus) mandibles retrieved from sediment cores to determine if planktivorous fish were present in these lakes prior to this century. I determined that C. (subgenus Chaoborus) americanus is the only species found in fishless lakes, while C. (C.) flavicans is only found in lakes containing fishes. The genus Chaoborus also had a restricted distribution along the elevation-temperature gradient of mountain lakes.

Cabin and Celestine lakes were fishless prior to this century. In these lakes, C. americanus was present prior to this century but was eliminated when fish were first stocked. C. flavicans has replaced C. americanus in Celestine Lake but Chaoborus are presently rare in Cabin Lake. The occurrence of C. flavicans throughout the Caledonia Lake core suggests that this lake had native fish(es) prior to this century. Paleolimnological analysis supports the hypothesis of the past occurrence of the Athabasca rainbow trout (O. mykiss athabascae) in Caledonia Lake. (Abstract shortened by UMI.)