Stable Oxygen and Carbon Isotopic Compositions of Lates stappersii Otoliths from Lake Tanganyika, East Africa

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Résumé

In this study, we measured growth trends in oxygen and carbon isotopic ratios in whole sagittal otoliths from three adult centropomid fish (Lates stappersii) from each of three sub-basins of Lake Tanganyika, East Africa. Sampling density was 20 to 50 samples per otolith. Both d 18C values increase with age. The d 18O and d 13O data suggest that otoliths were precipitated near the expected equilibrium with the ambient environment (ca. +3.5‰) and support a migration pattern from surface waters during larval stages to deeper waters (40 to 80 m) for mature fish. Relatively high d18O values in the southern sub-basin are consistent with cooler temperatures in the region during seasonal upwelling. The d 13 C increase from otolith core to edge is large (up to 4‰) and is interpreted as due to ontogenetic changes in diet and contributions from a decrease in the proportion of respired CO2 incorporated into otolith carbonate as metabolic rates of the fish dropped with maturity. The data seem to successfully reveal life strategy and migration patterns of L. stappersii, document regional differences in lake conditions, and provide a record of temperature within the water column during which the fish lived. Higher resolution studies and analyses of historical samples could be used to constrain modern and past growth patterns, and to reconstruct past temperature gradients and productivity patterns in the lake.

Mots-clés

Ontogeny, d 13O, temperature, growth profiles, sub-basins, ambient environment C and d 183