Assessing short and long-term isotopic niche patterns of three Delphinidae species in the South-West Atlantic Ocean

Description

The present study aims to evaluate the pattern in isotopic niche area and spatial/trophic overlap of three Delphinidae species from the Southwest Atlantic Ocean (SWAO). We measured carbon (δ13C) and nitrogen (δ15N) stable isotopes to compare long-term (tooth samples, life-span information) and short-term (skin samples, up to a few months) data of three delphinid species. The tooth samples were obtained from stranded animals during systematic beach monitoring along the southernmost coast of Brazil (1977-2014), while the skin samples were collected during ten spring and fall oceanographic cruises along the outer continental shelf and slope in the SWAO (2009-2015). The isotopic niche area (Standard Ellipse Area - SEAc) of each species, as well the peer-to-peer isotopic niche overlap percentage between species were calculated using the Stable Isotope Bayesian Ellipses in R. Steno bredanensis (ntooth=20; nskin=7) had the highest δ13C and δ15N values in both tissues, and showed no (in skin) or very low (in teeth) isotopic niche overlap with Delphinus delphis (ntooth=10; nskin=55) and Stenella frontalis (ntooth=9; nskin=74). Moreover, its isotopic niche was substantially larger for teeth (SEAc= 2.24) than for skin (SEAc= 0.32) tissues. D. delphis and S. frontalis showed similar isotopic niche area for both teeth (SEAc=1.53 and SEAc=1.92, respectively) and skin samples (SEAc=1.96 and SEAc=1.96). Both tissues showed isotopic niche overlap, although overlap was larger for teeth (47%) than for skin (17%) samples. Although our results suggest the occurrence of short and long-term overlap in resource use between D. delphis and S. frontalis, recent studies have shown that the density of the former decreases as that of the latter increases. The isotopic niche overlap estimated by our models could indicate similar resource use, although individuals of both species were not sharing the same resources at the same time. Teeth samples represent life-span dietary information, thus the temporal or seasonal isotopic variation regarding changes in feeding habits or changes in the environmental isotopic signal cannot be controlled. This is more evident as the models using the skin signal (thus seasonal isotopic signal) had considerably lower overlap, in comparison with results of models using teeth values.

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