| Summary: | Stable isotope analysis (SIA) of fish otoliths shows great potential for exploring the
ecology of fish, but this method has not been applied to the study of lacustrine fish
communities. Both sequential and whole-otolith SIAs were performed on six fish species of
Lake Annecy and their results compared to muscle SIA. The first purpose of these
investigations was to test the use of δ18Ooto values for reconstructing
fish thermal history and delimiting spatial distribution in a stratified lake. Comparison
of species-specific fractionation equations and the general equation developed for
freshwater fishes showed that the general one was the best suited for thermal estimation
of Lake Annecy fishes and suggested that inter-specific differences or specific “vital
effects” are not the only reason for apparent difference in fractionation. Thermal
estimations based on SIA were consistent with descriptions of thermal habitats in the
literature, except in the case of roach (Rutilus rutilus). Based on the
current results, roach appears to live in a colder habitat than do perch (Perca
fluviatilis). The high water transparency and thermal stratification of Lake
Annecy could explain this distribution. Moreover, perch juveniles were found to live in
two different thermal niches. This finding highlights the great plasticity of the species.
Second, the potential use of δ13Coto values to reconstruct
variation in diet and metabolism was assessed. The proportion of metabolic carbon
(M)
contributing to otolith carbon varies markedly among species. Comparison with
δ13Cmuscle values shows no direct
relationship between δ13Coto and diet at either the
intra-individual or the inter-specific level. A strong linear relationship between either
M or the
isotopic offset between otolith and muscle (Δδ13Coto - muscle) and δ18Ooto values was found; this
relationship reveals the dependence of M on the ambient temperature at which the species
occurs. This relationship might be general and could be used to explore variation in fish
metabolism in the future.
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