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Marine Ecology Progress Series

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MEPS 422:291-302 (2011)  -  DOI:

Stable isotopes reveal inter-annual and inter-individual variation in the diet of female Australian fur seals

J. P. Y. Arnould1,*, Y. Cherel2, J. Gibbens3, J. G. White1, C. L. Littnan4

1School of Life and Environmental Sciences, Deakin University, 221 Burwood Highway, Burwood, Victoria 3125, Australia
2Centre d’Etudes Biologiques de Chizé, UPR 1934 du CNRS, BP 14, 79360 Villiers-en-Bois, France
3Department of Zoology, University of Melbourne, Parkville, Victoria 3010, Australia
4Pacific Island Fisheries Science Center (PIFSC), NOAA Fisheries, 2570 Dole Street, Honolulu, Hawaii 96822, USA

ABSTRACT: Understanding the temporal and spatial variation of foraging habits of apex predators is central to understanding their role in marine ecosystems and how their populations may respond to environmental variability. In the present study, stable isotope analysis (C and N) of blood was used to investigate inter-individual and inter-annual differences in the diet of adult female Australian fur seals Arctocephalus pusillus doriferus. Positive correlations were observed between red cell and plasma values for δ13C and δ15N (r2 = 0.47 and r2 = 0.66, respectively, p < 0.001 in both cases), suggesting relatively consistent individual prey choices over 3 or 4 foraging trips. Mean δ15N values (12.8 to 17.5‰) confirm the species occupies the highest marine trophic niche in the region. A significant decrease in plasma δ15N values, corresponding to two-thirds of a trophic level (ca. 2‰), was observed between the 1998 to 2000 and 2003 to 2005 sampling periods. This was associated with a significant decrease in adult female body condition and is consistent with a decline, previously documented by faecal analysis, of the proportion of red cod Pseudophysis bachus, barracouta Thyrsites atun and Gould’s squid Nototodarus gouldi in the diet and an increase in redbait Emmelichthys nitidus. While substantial variation in δ15N was observed within each age cohort, a significant decrease was observed with age, suggesting individual specialisation for particular prey types is evident early in adulthood, but that its composition changes as females age. In addition, generalized linear models indicated body mass had a negative influence on δ15N, which may reflect larger total body oxygen stores, facilitating individuals hunting cryptic prey of lower trophic level (e.g. octopus) on the sea floor.

KEY WORDS: Australian fur seal · Otariid · Stable isotopes · Diet · Bass Strait · Arctocephalus pusillus doriferus

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Cite this article as: Arnould JPY, Cherel Y, Gibbens J, White JG, Littnan CL (2011) Stable isotopes reveal inter-annual and inter-individual variation in the diet of female Australian fur seals. Mar Ecol Prog Ser 422:291-302.

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