Ontogenetic dietary changes in male South American fur seals in northern and central Patagonia, Argentina

VALES DAMIÁN GUILLERMO; CARDONA LUIS; GARCÍA NÉSTOR ANÍBAL; ZENTENO LISETTE; AGUILAR ALEJANDRO; CRESPO ENRIQUE ALBERTO

MARINE ECOLOGY PROGRESS SERIES

INTER-RESEARCH

Lugar: Oldendorf/Luhe; Año: 2015 vol. 525 p. 245 - 260

0171-8630

ABSTRACT: This study assessed ontogenetic dietary changes in male South American fur sealsArctocephalus australis in northern and central Patagonia (Argentina) using stable isotope ratios(δ15N and δ13C) in vibrissae and bones. Sucking pups were characterised by higher δ15N valuesand lower δ13C values than older specimens. Weaning was associated with a marked drop of δ15Nvalues, both in bone and vibrissae. Such a drop was inconsistent with the consumption of localprey and may reveal movement to distant foraging grounds or physiological changes associatedwith either fasting or rapid growth. Stable isotope ratios indicated that juveniles fed more pelagicallythan subadults and adults, but that there were no major differences between the 2 latter agecategories. As subadults and adults are rather similar in body mass and are much larger than juveniles,body mass may play a role in the ontogenetic dietary changes reported. Nevertheless, de -mersal benthic prey were always scarce in the diet of male fur seals, which relied primarily onArgentine shortfin squid and small pelagic fish throughout life, though adults also consumed largeamounts of decapod crustaceans available at shallow depths. Vibrissae did not reveal regularoscillations of δ15N or δ13C, except in 1 individual. Thus, male fur seals from northern and centralPatagonia do not appear to migrate regularly between isotopically distinct areas, althoughnomadic displacements cannot be ruled out.