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Blubber fatty acids reveal variation in the diet of male Australian fur seals

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Abstract

Top-order predators play an important role in the structure and function of marine ecosystems. Optimal foraging theory predicts that predators will utilise foraging strategies that maximise their net energetic intake, and consequently, individuals within a population may utilise alternate strategies to target different prey resources. The present study investigated variation within the diet of 41 male Australian fur seals (Arctocephalus pusillus doriferus) using quantitative fatty-acid signature analysis (QFASA) of blubber. The study was conducted during the pre-breeding seasons of 2012 and 2013 and the non-breeding seasons of 2013 and 2014 at a colony on Kanowna Island (39°10′S, 146°18′E) in northern Bass Strait, southeastern Australia. QFASA models revealed that while males consumed prey commonly reported within the diet of Australian fur seals, elasmobranchs were more important than previously reported. Prey composition also varied between males which may reflect individuals using different strategies to target different resources, which ultimately broadens the trophic niche of a species and reduces intra-specific competition. Furthermore, substantial temporal variation in male diet was apparent presumably reflecting variation in the distribution, availability, and abundance of prey resources within Bass Strait at the time of sampling. Given that the energetic content of prey is expected to differ between species, temporal variation in dietary composition presumably has important implications for the growth and reproductive success of males.

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Data availability statement

The seal fatty-acid data analyzed during the current study are available from the corresponding author on reasonable request.

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Acknowledgements

We thank the many volunteers who gave their time to help in the field, in particular M. Lim, A. Fromant, J. Heritage, M. Zamora, and L. Andre. We thank P. Nichols for access to the raw prey fatty-acid data. Logistical support was provided by G. Boyd from Prom Adventurer boat charters, and Parks Victoria.

Funding

Financial support was provided by research grants from the Winifred Violet Scott Trust and Holsworth Wildlife Research Endowment.

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Authors and Affiliations

  1. School of Life and Environmental Sciences (Burwood Campus), Deakin University, Geelong, VIC, 3220, Australia

    T. C. Knox, D. L. Callahan, L. Kernaléguen, A. M. M. Baylis & J. P. Y. Arnould

  2. South Atlantic Environmental Research Institute, Stanley, FIQQ1ZZ, Falkland Islands

    A. M. M. Baylis

  3. Department of Biological Sciences, Macquarie University, Sydney, NSW, 2109, Australia

    A. M. M. Baylis

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  1. T. C. Knox
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Contributions

TCK and JPYA conceived the study. TCK, LK, AMMB, and JPYA conducted the fieldwork. TCK and DLC conducted the laboratory analyses. TCK analyzed the data, with input from JPYA and AMMB. TCK wrote the paper, with assistance from DLC, AMMB, and JPYA.

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Correspondence to T. C. Knox.

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All work was carried out with the approval of the Deakin University Animal Ethics Committee and under Department of Environment, Land, Water, and Planning (Victoria, Australia) wildlife research permits (A71-2011, B12-2013, 10005848, 1007153).

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Knox, T.C., Callahan, D.L., Kernaléguen, L. et al. Blubber fatty acids reveal variation in the diet of male Australian fur seals. Mar Biol 166, 117 (2019). https://doi.org/10.1007/s00227-019-3552-y

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