Stable isotope profiles in whale shark (Rhincodon typus) suggest segregation and dissimilarities in the diet depending on sex and size

We investigated the sex- and size-related differences in the diet of whale sharks from the Arabian Sea (north-western Indian Ocean) using carbon and nitrogen stable-isotope analyses in white muscle. The samples were collected during the commercial fishing season between April and May of 2001 in Veraval (Gujarat, India). The overall isotope signature was similar to that of the pelagic-neritic zooplanktivore Ilisha melastoma, which suggests that both species are feeding on similar prey. In whale sharks, a positive relationship was found between delta N-15 and delta C-13. This, together with a significant enrichment of both heavy stable isotopes with total length indicates that the contribution to the diet of small fish and/or larger zooplankton of higher trophic level increases with the movement from offshore areas to coastal areas as they grow. Gender differences in the isotopic ratios were not statistically significant, but small sample size cannot rule out completely the existence of some degree of spatial or dietary segregation between sexes.