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Detailed knowledge on habitat use by marine mammals is critical for understanding their ecological role and for adequate management. Here, we assess the habitat use patterns of thirteen species of marine mammals along the salinity gradient of the Río de la Plata estuary and the adjoining western South Atlantic Ocean, for which we use the ratios of stable oxygen isotopes in bone carbonate (apatite) as a proxy for salinity. Furthermore, we compare the results with those found from analysing the distance of the stranding site from the innermost point of the estuary. The overall evidence indicates that stable oxygen isotopes can be good tracers of habitat use, as they distinguish those species that regularly use inshore estuarine-coastal ecosystems from those that are restricted to offshore pelagic oceanic waters. In contrast, sampling location does not sufficiently characterize the species' habitat, since other factors can be involved in the animals being transported to stranding sites far from their typical habitats. In conclusion, the analysis of stable oxygen isotopes represents a useful and inexpensive approach to studying habitat use among marine mammals where salinity gradients exist. Image 1 • The average δ18O values in bone tissue differs between species. • There is good agreement between presumed habitat along a salinity gradient and δ18O values in bone. • Inshore species had lower bone δ18O values than offshore dwellers. • The δ18O values predict habitat better than they do stranding location. [ABSTRACT FROM AUTHOR]

The taxonomy and distribution patterns of the common dolphins (genus Delphinus) are problematic among cetaceans and particularly complicated in the south-western Atlantic Ocean. On the basis of national collections, we found ten adult skulls of the genus Delphinus of Uruguayan origin. The two currently recognized species for the genus were identified based on craniometric measurements: the pelagic short beaked form (Delphinus delphis, N = 3) and the coastal long beaked form (Delphinus capensis, N = 4), although previous studies only recognized D. capensis for Uruguay. Three specimens could not be identified (Delphinus sp.) because of broken skull (2) and intermediate measures (1). This result is consistent with a recent review on the biogeography of the genus in the south-western Atlantic Ocean. [ABSTRACT FROM AUTHOR]

Lead (Pb) is a trace element that is naturally present in arid regions but it is also released to the marine environment by anthropogenic industrial emissions. Here, we assessed Pb concentrations in bone samples of four pinniped species: the Galapagos sea lion Zalophus wollebaeki , sampled in Galapagos archipelago, the monk seal Monachus monachus from Mauritania, and the South American fur seal Arctocephalus australis and the South American sea lion Otaria flavescens , from Uruguay, and investigate potential geographic differences. Concentrations of lead in the samples from Galapagos were lower than those detected in samples from Mauritania and Uruguay, indicating that the Galapagos archipelago is a comparatively pristine spot for this toxic element as related to the other two areas. The waters of Mauritania and Uruguay are likely affected by the inputs of lead brought by the desert dust and released by the local industry, respectively. This study supports the use of bone to assess lead concentrations in biota, as well as the use of pinnipeds as bioindicators of marine pollution. [Display omitted] • Lead was analysed in the bone of four pinniped species from three marine areas. • The lowest lead concentrations occurred in pinnipeds from the Galapagos archipelago. • Lead concentrations were higher in pinnipeds from Mauritania and Rio de la Plata. • In Mauritanian waters, the likely origin of lead was wind-brought Sahara dust. • In Rio de la Plata waters, the likely origin of lead was industrial activities. [ABSTRACT FROM AUTHOR]

The main aim of this work was to evaluate historical changes in the foraging ecology of Lahille's bottlenose dolphin (Tursiops truncatus gephyreus) along its distributional range. Stable isotopes of carbon (δ13C) and nitrogen (δ15N) were analyzed in bone samples from specimens deposited in scientific institutions from Brazil (BR), Uruguay (UY) and Argentina (ARG), collected in periods PI (1903–1980) and PII (1981–2016). The isotopic values of ARG dolphins were different from UY and BR in both periods, reflecting variations in the composition of the diet and/or basal isotopic values. The considerably broad isotopic niche of the ARG dolphins was maintained in PII, following the trend of stable carbon and nitrogen isotopic values along the decades. In this area, mixing models showed a diet with a high proportion of demersal prey, mainly from coastal marine waters. Lahille's bottlenose dolphins from UY showed a stability in nitrogen isotopic values but increasing carbon isotope values through decades. This increasing trend was consistent with a lower use of the Río de la Plata estuarine waters by the species reported for the last decades. In these areas, the species also showed a high proportion of demersal fish species. Finally, ARG and UY dolphins showed a partial and a total isotopic niche segregation during Periods I and II, respectively, probably reflecting a spatial/ecological structuring in this region. BR and UY samples, on the other hand, were not statistically different, probably forming an ecological unit. The retrospective analysis of the Lahille's bottlenose dolphin diet contributed to the knowledge of the ecological structure and feeding behavior of this poorly-known subspecies. [Display omitted] • Lahille's bottlenose dolphins from ARG maintained a broad isotopic niche along decades • In UY and ARG the species seemed to forage upon demersal prey from the Atlantic coastal marine area • Lower δ13C values in UY historic samples reflected the past use of the estuary • Isotopic niche segregation of ARG and UY showed a spatial and ecological structuring • BR and UY, with a high overlap in isotopic niches, are probably an ecological unit [ABSTRACT FROM AUTHOR]