Abstract: Stable carbon and nitrogen isotope ratios (δ¹³C and δ¹⁵N, respectively) of multiple tissues with different turnover rates can provide trophic information at different timescales, and thus play an important role in tracing the changes of feeding, habitat utilization and trophic niche of consumers. The δ¹³C and δ¹⁵N contents of muscle, liver and blood of blue sharks (Prionace glauca), longfin mako sharks (Isurus paucus), crocodile sharks (Pseudocarcharias kamoharai) and shortfin mako sharks (I. oxyrinchus) from tropical Atlantic were measured, and the trophic niche was evalua-ted. The results showed that I. oxyrinchus, P. kamoharai, and P. glauca had similar δ¹⁵N values, higher than that of I. paucus. Feeding segregation was found between P. glauca and other species, showing unique trophic niche. The largest trophic niche width was observed in I. oxyrinchus, indicating the high diversity of prey and (or) feeding habitats. High trophic niche overlap was found in P. kamoharai and I. oxyrinchus, implying their potential competition for resources. There was no correlation between the differences among tissues in the δ¹³C or δ¹⁵N values and the body size of I. oxyrinchus, P. kamoharai and P. glauca, indicating no recent diet shifts for those species. I. paucus showed significant correlation between δ¹⁵N differences in liver, blood and muscle with the shark fork length, indicating its short-term diet shift. The similarity of δ¹³C and δ¹⁵N values and the higher metabolic rates of liver and blood were found in all four shark species, implying the similar incorporation rates of both tissues, which were considered as the short-term indicator of diet.

Key words: tropical Atlantic, pelagic shark, tissue turnover, stable isotope, trophic ecology