Wildlife Research Wildlife Research Society
Ecology, management and conservation in natural and modified habitats
RESEARCH ARTICLE

Assessing the use of milk fatty acids to infer the diet of the Australian sea lion (Neophoca cinerea)

A. M. M. Baylis A B C F , D. J. Hamer A B and P. D. Nichols D E
+ Author Affiliations
- Author Affiliations

A School of Earth and Environmental Sciences, University of Adelaide, Adelaide, SA 5005, Australia.

B South Australian Research and Development Institute (Aquatic Sciences), PO Box 120, Henley Beach, Adelaide, SA 5022, Australia.

C Present address: Falkland Islands Government, Fisheries Department, PO Box 598, Stanley, Falkland Islands.

D CSIRO Marine and Atmospheric Research, Food Futures Flagship, GPO Box 1538, Hobart, TAS 7001 Australia.

E Antarctic and Climate Ecosystems Cooperative Research Centre, University of Tasmania, Private Bag 80, TAS 7001, Australia.

F Corresponding author. Email: al_baylis@yahoo.com.au

Wildlife Research 36(2) 169-176 https://doi.org/10.1071/WR08046
Submitted: 24 March 2008  Accepted: 19 August 2008   Published: 20 February 2009

Abstract

Information on the diet of threatened species is important in devising appropriate management plans to ensure their conservation. The Australian sea lion (Neophoca cinerea) is Australia’s only endemic and globally one of the least numerous pinniped species. However, dietary information is currently limited because of the difficulty in using traditional methods (identification of prey hard parts from scats, regurgitates and stomach samples) to reliably provide dietary information. The present study assessed the use of fatty acid (FA) analysis to infer diet using milk samples collected from 11 satellite tracked Australian sea lions from Olive Island, South Australia. Satellite tracking revealed that females foraged in two distinct regions; ‘inshore’ regions characterised by shallow bathymetry (10.7 ± 4.8 m) and ‘offshore’ regions characterised by comparatively deep bathymetry (60.5 ± 13.4 m). Milk FA analysis indicated significant differences in the FA composition between females that foraged inshore compared with those that foraged offshore. The greatest differences in relative levels of individual FAs between the inshore and offshore groups were for 22 : 6n-3 (6.5 ± 1.2% compared with 16.5 ± 1.9% respectively), 20 : 4n-6 (6.1 ± 0.7 compared with 2.5 ± 0.7 respectively) and 22 : 4n-6 (2.4 ± 0.2% compared with 0.8 ± 0.2% respectively). Using discriminant scores, crustacean, cephalopod, fish and shark-dominated diets were differentiated. The discriminant scores from Australian sea lions that foraged inshore indicated a mixed fish and shark diet, whereas discriminant scores from Australian sea lions that foraged offshore indicated a fish-dominated diet, although results must be interpreted with caution due to the assumptions associated with the prey FA dataset. FA analysis in combination with satellite tracking proved to be a powerful tool for assessing broad-scale spatial dietary patterns.


Acknowledgements

This study was supported through National Heritage Trust (NHT) grants scheme, Nature Foundation SA, Wildlife Conservation Fund, Holsworth Wildlife Fund, MA Ingram trust and the Sea World Research and Rescue Foundation. A.M.M.B. and D.J.H were recipients of an Australian Postgraduate Award. We thank S. Goldsworthy for securing NHT funding, W. Hutchison for assistance in the field and M. Miller, B. Mooney, M. Guest, D. Holdsworth and P. Mansour (CSIRO Marine and Atmospheric Research) who provided guidance with sample preparation and FA extraction. We also extend thanks to T. M. Ward (SARDI) and D. Paton (Adelaide University) for their continued support. K. Peters, R. McIntosh and T. M. Ward provided helpful comments on earlier drafts of the manuscript. The valuable comments of two anonymous reviewers and the editor, Andrea Taylor, are also gratefully acknowledged. This research was conducted under the Department for Environment and Heritage permit A24684-3 and Adelaide University ethics permit S-008-2007.


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