On the uptake and elimination of stable nitrogen isotopes in elasmobranchs
MacNeil, M. Aaron
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Stable isotopes of carbon and nitrogen are often used to explore the trophic-dynamics of marine fishes; however, little is known about their kinetics in fish tissues — particularly elasmobranchs. I conducted a laboratory study on 15N kinetics in freshwater stingray Potamotrygon motoro and a field study of inter-tissue stable isotope ratios in blue Prionace glauca, mako Isurus oxyrinchus, and thresher Alopias vulpinus sharks. Stingray tissues showed different rates of 15N uptake and elimination, suggesting that muscle samples alone may bias 15N-derived trophic estimates and that multiple tissues should be collected in field studies. The field study of multiple-tissue stable isotope ratios captured known dietary shifts in I. oxyrinchus and indicated generalist diets for P. glauca and A. vulpinus. I concluded that laboratory work of the kind presented is necessary for stable isotope analysis of trophic dynamics to be empirically sound.