Marine Biology

, 165:59 | Cite as

Historical age-class diet changes in South American fur seals and sea lions in Uruguay

  • Diana Szteren
  • David Aurioles-Gamboa
  • Vanessa Labrada-Martagón
  • Claudia J. Hernández-Camacho
  • Maite De María
Original paper

Abstract

Pinnipeds are effective bioindicators of the abundance of their prey and changes in marine productivity due to natural oceanographic phenomena or fishery exploitation. In Uruguay, two pinniped species breed sympatrically: Arctocephalus australis, with a growing population, and Otaria flavescens, which has a declining population. Given their contrasting population growth trends, we explored how their trophic patterns varied across age-classes over seven decades using dentin collagen δ13C and δ15N values in teeth sampled from stranded organisms. Dentin collagen accumulates isotopic information in annual growth layers, providing sequential information on an animal’s diet throughout its life. Dentin collagen annual growth layers in 50 A. australis teeth and 37 O. flavescens teeth from individuals stranded over ~ 70 years were processed for isotopic analysis. Importantly, δ13C decreased over time in both species (0.024–0.027‰ year–1 in A. australis, and 0.028–0.035‰ in O. flavescens); this pattern reflects the influence of the Suess Effect, a global phenomenon of decreasing δ13C values in marine ecosystems. Isotopic values were relatively constant over time, suggesting that these species maintained a stable trophic niche during the seven decades examined, with O. flavescens exhibiting higher δ13C and δ15N values. Within each species, there was considerable isotopic niche overlap between different age-classes; however, both species occupied different isotopic niches regardless of age-class during all decades. The isotopic niches of the two species converged during the 2000s. Primarily responsible for this convergence were adult A. australis, which overlapped with juvenile and young adult O. flavescens. Moreover, we propose that before the 2000s A. australis fed on prey from different trophic levels while O. flavescens varied its feeding habitat. Our results suggest that these top predators reflect anthropogenic and environmental changes that have occurred over the last seven decades in Uruguayan waters.

Notes

Acknowledgements

The Museo Nacional de Historia Natural (MNHN; National Museum of Natural History) and the zoological collection of the Faculty of Sciences at the Universidad de la República (University of the Republic), both in Uruguay, generously provided us access to their scientific collections to sample teeth for this study. We thank Maricela Juárez for training DS in laboratory techniques and assisting with sample processing, Patricia Rosas-Hernández for helping with the SIBER graphics, and Sabrina Riverón for her collaboration in the field and in cleaning skulls. This study was funded by the National Geographic Society Committee for Research and Exploration (Grant #8978-11). The Comisión Sectorial de Investigación Científica (CSIC; Sectorial Commission for Scientific Research) funded two research trips for DS. Thanks to the Instituto Politécnico Nacional (IPN; National Polytechnic Institute) for a sabbatical grant to D.A.G., and to the Centro Interdisciplinario de Ciencias Marinas (Interdisciplinary Center for Marine Science) for access to laboratory space and equipment. We thank Kristin Sullivan for editing the English text and the two reviewers for their helpful comments on this manuscript.

Compliance with ethical standards

Conflict of interest

The authors declare no conflict of interest.

Ethical approval

This article does not contain any research on live animals performed by any of the authors. Permission to collect teeth from the skulls of pinnipeds stranded on the Uruguayan coast was obtained from the Dirección Nacional de Recursos Acuáticos, Ministerio de Ganadería Agricultura y Pesca (DINARA-MGAP, National Direction for Aquatic Resources of the Ministry of Livestock, Agriculture, and Fisheries in Uruguay) as permit number 737/2006.

Supplementary material

227_2018_3315_MOESM1_ESM.pdf (280 kb)
Supplementary material 1 (PDF 279 kb)

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Authors and Affiliations

  1. 1.Laboratorio de Zoología Vertebrados, Departamento de Ecología y Evolución, Facultad de CienciasUniversidad de la RepúblicaMontevideoUruguay
  2. 2.Laboratorio de Ecología de Pinnipedos “Burney J. Le Boeuf”, Centro Interdisciplinario de Ciencias MarinasInstituto Politécnico NacionalLa PazMexico
  3. 3.Facultad de CienciasUniversidad Autónoma de San Luis PotosíSan Luis PotosíMexico

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