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Marine Ecology Progress Series

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MEPS 525:261-272 (2015)  -  DOI: https://doi.org/10.3354/meps11236

Sexual foraging segregation in South American sea lions increases during the pre-breeding period in the Río de la Plata plume

M. Drago1,*, V. Franco-Trecu2, L. Zenteno3, D. Szteren4, E. A. Crespo5, F. G. Riet Sapriza2,8, L. de Oliveira6, R. Machado6,7, P. Inchausti1, L. Cardona3

1Department of Ecology & Evolution, Centro Universitario Regional Este (CURE), University of the Republic, C/ Tacuarembó s/n, 20000 Maldonado, Uruguay
2Proyecto Pinnípedos, Sección Etología, Facultad de Ciencias, Universidad de la República, Iguá 4225, 11400 Montevideo, Uruguay
3IRBIO and Department of Animal Biology, Faculty of Biology, University of Barcelona, Av. Diagonal 645, 08028 Barcelona, Spain
4Dpto de Ecología y Evolución, Facultad de Ciencias, Universidad de la República, Iguá 4225, 11400 Montevideo, Uruguay
5Laboratory of Marine Mammals, Centro Nacional Patagonico (CENPAT-CONICET), and National University of Patagonia, Blvd. Brown 3600, 9120 Puerto Madryn, Chubut, Argentina
6Study Group of Aquatic Mammals of Rio Grande do Sul (GEMARS), Av. Tramandaí 976, RS 95625-000, Imbé, Brazil
7Laboratório de Sistemática e Ecologia de Aves e Mamíferos Marinhos (LabSMar), Departamento de Zoologia/IB, Universidade Federal do Rio Grande do Sul (UFRGS), Av. Bento Gonçalves 9500, RS 91509-900, Porto Alegres, Brazil
8Present address: Lab. de Ecología Molecular de Vertebrados Acuáticos (LEMVA), Departamento Ciencias Biológicas, Facultad de Ciencias, Universidad de los Andes, Carrera 1E No 18A - 10, Bogotá, Colombia
*Corresponding author:

ABSTRACT: Stable carbon and nitrogen isotopes in skin and bone of South American sea lions from Brazil and Uruguay were analysed to test the hypothesis that trophic overlap between the sexes is lower during the pre-breeding season than throughout the rest of the year. The isotopic values of skin and bone were used to infer the trophic relationships between the sexes during the pre-breeding period and year round, respectively. Prey species were also analysed to establish a baseline necessary for interpreting the stable isotope ratios of skin and bone. Standard ellipse areas, estimated using Bayesian inference in the SIBER routine of the SIAR package in R, suggested that males and females used a wide diversity of foraging strategies throughout the year and that no differences existed between the sexes. However, the diversity of foraging strategies was largely reduced during the pre-breeding period, with all the individuals of each sex adopting similar strategies, but with the two sexes differing considerably in stable isotope values and the ellipse areas of males and females not overlapping at all. Nevertheless, the results revealed a general increase in the consumption of pelagic prey by both sexes during the pre-breeding period. The progressive crowding of individuals in the areas surrounding the breeding rookeries during the pre-breeding period could lead to an increase in the local population density, which could explain the above reported changes.


KEY WORDS: Otaria flavescens · Sexual foraging segregation · Skin · Bone · Stable isotope Bayesian ellipses


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Cite this article as: Drago M, Franco-Trecu V, Zenteno L, Szteren D and others (2015) Sexual foraging segregation in South American sea lions increases during the pre-breeding period in the Río de la Plata plume. Mar Ecol Prog Ser 525:261-272. https://doi.org/10.3354/meps11236

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