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Diet of New Zealand sea lions (Phocarctos hookeri) at their southern breeding limits

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Abstract

The New Zealand (NZ) sea lion (Phocarctos hookeri) is endemic to NZ and is listed as “Vulnerable” by the International Union for Conservation of Nature. Approximately 99 % of pups are born at the Auckland Islands (a declining population) and Campbell Island (a growing population). The causes of contrasting population trajectory are not well understood, though spatial and temporal variations in prey availability have frequently been implicated for other pinnipeds. This is the first published diet study of the Campbell Island population, located at the species’ southern breeding limit. Prey species were identified and quantified from scats and regurgitate samples collected in March 2013 (n = 159 and 7, respectively). An array of prey taxa was identified, though two species were particularly dominant in terms of reconstituted diet mass (M) of fishes and cephalopods: small-scaled cod (Notothenia microlepidota), which dominated scat samples (50 % M); and yellow octopus (Enteroctopus zealandicus), which dominated a small sample of regurgitates (72 % M). The diet lacked many of the key prey taxa of the Auckland Islands, and we hypothesise that the key prey identified here provides a highly available food source for the growing population of NZ sea lions at Campbell Island. These differences are likely to reflect spatial heterogeneity in prey availability and may be one of the main causes of an increase in NZ sea lion population size at Campbell Island in contrast to a decrease at the Auckland Islands.

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Acknowledgments

This research was supported by the NIWA Core Funding Program and the NZ Department of Conservation. We would like to thank Mary-Anne Lea, Mark Hindell (both University of Tasmania, Australia), Kimberley Vinette Herrin (Sydney Zoo, Australia) and Robert Mattlin (Marine Wildlife Research, NZ) for assistance with the collection of samples. Also Jeff Forman for the identification of invertebrate prey items and Darren Stevens (both NIWA, NZ) for assistance with identification from cephalopod beaks and Alan Tennyson and Colin Tinkler (both Te Papa Museum, NZ) for tentative identifications from bird feathers. All samples were collected in accordance with ethical conditions specified in the NZ Department of Conservation Research Permit Number 35879-FAU. CL thanks Sanford Ltd for permission to collect specimen fish, cephalopod and crustaceans aboard their chartered trawlers. Finally, we thank the four reviewers who provided appreciated suggestions for improving this manuscript.

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Authors and Affiliations

  1. National Institute of Water and Atmospheric Research, 301 Evans Bay Parade, Hataitai, Private Bag 14901, Wellington, 6021, New Zealand

    J. Roberts

  2. Department of Marine Science, University of Otago, PO Box 56, Dunedin, 9054, New Zealand

    C. Lalas

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  1. J. Roberts
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  2. C. Lalas
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Correspondence to J. Roberts.

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Roberts, J., Lalas, C. Diet of New Zealand sea lions (Phocarctos hookeri) at their southern breeding limits. Polar Biol 38, 1483–1491 (2015). https://doi.org/10.1007/s00300-015-1710-3

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