Stable Carbon and Nitrogen Isotopes Show Evidence of Resource Partitioning Between Spinner Dolphins (Stenella longirostris) and Large Pelagic Fishes From the Fernando de Noronha Archipelago

Abstract

We applied stable carbon and nitrogen isotopes to investigate the trophic ecology of four large pelagic predators from the Fernando de Noronha Archipelago (FNA), northeastern Brazil: spinner dolphin (Stenella longirostris), yellowfin tuna (Thunnus albacares), wahoo (Acanthocybium solandri), and great barracuda (Sphyraena barracuda). We found no significant divergences in δ13C and δ15N values or trophic positions between male and female spinner dolphins; and the high isotopic niche overlap indicated limited sexual segregation. Our data indicate overlap in the isotopic niches of yellowfin tuna, wahoo, and great barracuda, but significant segregation between these pelagic predators and spinner dolphins. While spinner dolphis occupy higher trophic positions, reflecting their consumption of mesopleagic squids, the fishes seem to target a broader prey spectrum, with yellowfin tuna showing a more specialized diet. This partitioning likely reduces interspecific competition for prey in the FNA, with different species occupying distinct ecological niches. The results presented here provide important information about the trophic relationships among pelagic predators from the FNA, which is crucial for their conservation in a region where they are vulnerable to local anthropogenic activities.