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Growth and survival of New Zealand sea lions, Phocarctos hookeri: birth to 3 months

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Abstract

Offspring birth mass and growth rate represent important life history traits, which influence many vital population and individual characteristics, while offspring survival is a key factor in variation in female reproductive success. For a threatened population of pinnipeds, such as New Zealand sea lions, Phocarctos hookeri, (Grey, 1844, NZ sea lions), understanding individual life history parameters and population dynamics is vital for their management and conservation. This is the first study of the behaviour of females during parturition, pup birth mass and growth, and pre-weaning survival of NZ sea lions, Enderby Island, Auckland Islands during austral summer breeding seasons, 2001/2002 to 2003/2004. Pregnant females arrived ashore 2.1 ± 0.16 days prior to giving birth. After parturition, mothers suckled their pups for 8.6 ± 0.16 days before leaving on their first foraging trip. Male pups were born significantly heavier than female (males 10.6 ± 1.4 kg, females 9.7 ± 0.9 kg). Pups lost on average 48 ± 0.14 g per day mass during the early postpartum period (between birth and mothers first foraging trip). Pup mortality did not vary by pup sex, birth mass, date of birth or any maternal characteristics however it varied significantly between years due to a bacterial infection epidemic (Pup mortality at 60 days: 2001 32%; 2002 21%; 2003 12%). The absolute growth rate per day for pups was 151 g/day over all years. Pup growth rate measured as the slope of linear line fitted to pup mass by age was consistently higher for pups with heavier birth mass, male pups and during the 2002 season. High offspring mortality and slow growth rates coupled with maternal foraging behaviour at their physiological limits may reflect a threatened species which has limited ability for population growth in an environment which is at the extreme of their historical range and impacted upon by fisheries.

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Acknowledgments

The work was conducted under permit from the New Zealand Department of Conservation (DOC), and was funded by the Foundation for Research Science and Technology (FRST), DOC, Science and Research Unit and the University of Canterbury (Internal Research Grant U6347). DOC Southland are thanked for their logistical assistance. We also thank J. Amey, H. Best, A. Castinel, W. Hockley, F. Jonker, A. Maloney, F. Riet Sapriza, M. Stratton and M. Wylie for assistance with captures in the field. Approval for work was obtained from DOC Animal Ethics Committee—Approval AEC86 (1 July 1999). I. West and two anonymous reviewers all provided helpful, critical reviews of the manuscript. This research was conducted while B.L.C. held a Foundation for Research, Science and Technology Fellowship contract (UOCX0105) and B.C.R. held a University of Canterbury Postdoctoral Fellowship (U2016).

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Correspondence to B. Louise Chilvers.

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Chilvers, B.L., Robertson, B.C., Wilkinson, I.S. et al. Growth and survival of New Zealand sea lions, Phocarctos hookeri: birth to 3 months. Polar Biol 30, 459–469 (2007). https://doi.org/10.1007/s00300-006-0203-9

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  • DOI: https://doi.org/10.1007/s00300-006-0203-9

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