Polar Biology

, Volume 37, Issue 1, pp 15–26 | Cite as

Size and experience matter: diving behaviour of juvenile New Zealand sea lions (Phocarctos hookeri)

  • Elaine S. Leung
  • B. Louise Chilvers
  • Shinichi Nakagawa
  • Bruce C. Robertson
Original Paper


The diving ability of juvenile animals is constrained by their physiology, morphology and lack of experience, compared to adults. We studied the influences of age and mass on the diving behaviour of juvenile (2–3-year-old females, n = 12; 3–5-year-old males, n = 7) New Zealand (NZ) sea lions (Phocarctos hookeri) using time–depth recorders (TDRs) from 2008 to 2010 in the NZ subantarctic Auckland Islands. Diving ability (e.g. dive depth, duration and bottom time per dive) improved with age and mass. However, the percentage of each dive spent at the bottom, along with percentage time at sea spent diving, was comparable between younger and lighter juveniles and older and heavier juveniles. These suggest that younger and older juveniles expend similar foraging effort in terms of the amount of time spent underwater. Only, 5-year-old male juveniles dove to adult female depths and durations and had the highest foraging efficiency at depths >250 m. It appears that juvenile NZ sea lions attain adult female diving ability at around 5 years of age (at least in males), but prior to this, their performance is limited. Overall, the restricted diving capabilities of juvenile NZ sea lions may limit their available foraging habitat and ability to acquire food at deeper depths. The lower diving ability of juvenile NZ sea lions compared to adults, along with juvenile-specific constraints, should be taken into consideration for the effective management of this declining, nationally critical species.


Age Mass Size Sex differences Lower diving ability Conservation management 



We thank A. Augé, L. Boren, H. McConnell, J. Amey, W. Roe, L. Meynier, K. Geschke, R. Hood, J. Fyfe, K. McInnes, N. McNally, G. Oakes and M. Riki for their assistance with animal captures. We are grateful to A. Jacob, S. Townsend, D. Jones, G. McDonald, S. Childerhouse and anonymous reviewers for their helpful comments on this manuscript. Data presented in this paper were collected from a long-term study funded by the New Zealand Department of Conservation (DOC) investigation no. 1638, in parallel with fieldwork undertaken for the DOC Conservation Services Program (DOC project Pop 2007/01; http://www.doc.govt.nz/conservation/marine-and-coastal/commercial-fishing/conservation-services-programme/) and through a levy principally on the quota holders of SQU6T. Funding was also provided by the University of Otago Zoology Department. Animal Ethics Committee Approval: DOC AEC158 (10 December 2007), DOC AEC 200 (2 November 2009) and University of Otago AEC 28/10. E.L. was supported by the University of Otago Postgraduate Scholarship.


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Copyright information

© Springer-Verlag Berlin Heidelberg 2013

Authors and Affiliations

  • Elaine S. Leung
    • 1
  • B. Louise Chilvers
    • 2
  • Shinichi Nakagawa
    • 1
  • Bruce C. Robertson
    • 1
  1. 1.Department of ZoologyUniversity of OtagoDunedinNew Zealand
  2. 2.Aquatic and Threats UnitDepartment of ConservationWellingtonNew Zealand

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