STABLE ISOTOPE ECOLOGY OF ALASKAN SOCKEYE SALMON LAKES.

Abstract

Stable isotope ratios of carbon and nitrogen (expressed as S^C and WN)are used in food web studies to trace sources of these elements when sources differ in their natural stable isotope abundance. In the case of Alaskan sockeye salmon nursery lakes, two sources of nitrogen exist which can be distinguished by WN,(1) marine-derived nitrogen from adult salmon carcasses, and (2) nitrogen derived from atmospheric N2. WNdata suggest that the proportion of marine nitrogen in sockeye salmon lake biota varies markedly with size of escapement. Measurements of S^C in combination with WN, when used to assess the contribution of three carbon sources to food webs, (1) adult salmon, (2) carbon derived from atmospheric C02, and (3)CO2 released during decomposition (respiration) of detritus, suggest shifts in the feeding habits of fishes in sockeye salmon lakes over space and time.