CANNIBALISM AND TROPHIC STRUCTURE IN A HIGH ARCTIC LAKE - INSIGHTS FROM STABLE-ISOTOPE ANALYSIS

Stable-nitrogen (N-15/N-14) isotope ratios (from 2.1 parts per thousan d in moss to 14.5 parts per thousand in Arctic char, Salvelinus alpinu s), showed enrichment with trophic level in the food web of Char Lake, Northwest Territories, and may be used to infer trophic position. The average N-15 enrichment of 1.5 parts per thousand between moss or alg ae and invertebrates suggests input to the food web of isotopically li ghter nitrogen than that measured for these sources of primary product ion. Stable-carbon (C-13/C-12) isotope ratios differed between moss an d algae by almost 10 parts per thousand and indicate that carbon in th e Char Lake food web is derived from a blend of these sources of prima ry production. Arctic char delta(15)N values for muscle tissue were po sitively correlated with fork length and clustered into three distinct groups: small fish (1-3 cm, mean delta(15)N = 5.7 parts per thousand) , which possibly consumed more benthic particles than previously assum ed; intermediate-size fish (10-35 cm, mean delta(15)N = 10 parts per t housand), which likely depended on larval char as well as their primar y zooplankton and chironomid prey; and larger Arctic char, which showe d a mean stepwise increase in delta(15)N of 3.7 parts per thousand. Th is suggests that complete cannibalism in this population generally occ urs abruptly and is exercised by a relatively small number of large in dividuals.