Isotopic niche of delphinids along the outer continental shelf and slope in south-southeastern Brazil

Description

Isotopic niche can be used as an indicator of predators' ecological niches, helping to describe their trophic positions, feeding areas, and the level of segregation or overlap in their resource use. Our study aims to characterize the trophic relationships among delphinids along the outer continental shelf and slope in south-southeastern Brazil. We measured carbon (δ13C) and nitrogen (δ15N) stable isotopes in skin samples of seven delphinid species obtained during ten spring and fall oceanographic cruises onboard the Federal University of Rio Grande' R.V. Atlântico Sul. Stable Isotope Bayesian Ellipses in R (SIBER) was applied to calculate the isotopic niche area (Standard Ellipse Area, SEAc) of each cetacean species and to estimate the level of niche overlap among them. Steno bredanensis (n=7) had the highest δ15N values (17.9±0.5‰), followed by Delphinus delphis (n=54, 15.3±1.5‰). Both species had higher δ13C values (-16.2±0.2‰ and -16.8±0.7‰, respectively) in comparison to the other species, and were associated with waters over the shelfbreak. Stenella longirostris (n=44) and S. attenuata (n=7) had both the lowest δ13C (-18.5±0.4‰ and -18.0±0.4‰) and δ15N values (11.3±0.6‰ and 11.8±0.7‰), indicating a further offshore distribution and relatively lower trophic positions. Tursiops truncatus (n=76), Stenella frontalis (n=74) and Orcinus orca (n=3) showed intermediate δ13C (-17.5±0.4‰, -17.5±0.6‰ and -17.6±0.2‰) and δ15N values (13.2±1.0‰, 13.5±1.5‰ and 12.8±0.1‰). These three species showed high isotopic spatial overlap, and SIBER estimated the highest isotopic niche overlap between T. truncatus and S. frontalis (45.9%). S. bredanensis' isotopic niche did not overlap with any other species. S. longirostris' isotopic niche overlapped only with S. attenuata (17%). S. frontalis and D. delphis had the largest SEAc estimated (SEAc = 1.96 each), followed by T. truncatus (SEAc = 1.3), suggesting a wide area of habitat used and more generalist feeding habits. Nevertheless, our analysis included data collected over six years, and this high within species isotopic variability might reflect seasonal or temporal dietary variation within the timeframe different individuals of a species were sampled. Finally, the results presented here reflect these species' known distribution areas, such as S. longirostris and S. attenuata's offshore occurrences, and D. delphis' association with upwelling waters.

Periode	27 nov 2016 → 2 dec 2016
Gehouden op	Reunión de Trabajo de Especialistas en Mamíferos Acuáticos de América del Sur y Congreso SOLAMAC
Mate van erkenning	International