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Population dynamics reveal conservation priorities of the threatened New Zealand sea lion Phocarctos hookeri

A Comment and reply to this article was published on 21 April 2016

Abstract

Understanding the life history basis of the population dynamics of threatened species is crucial to their assessment and recovery. Within the Southern Pacific Ocean, the decline and range contraction of New Zealand sea lions (NZSLs) (Phocarctos hookeri) are an exemplary case of a major fisheries and conservation controversy. Despite the use of bycatch reduction measures, the main population of the NZSL has declined since 1998 and its vulnerability to threats is poorly understood. Here we develop a population model for the declining population of the endangered NZSL at the Auckland Islands, New Zealand (\(50^{\circ }30^{\prime }\hbox {S}, 166^{\circ }17^{\prime }\hbox {E}\)), parameterised by mark-recapture data of 2928 female NZSLs spanning 15 years from 1998 to 2012, and provide the first comprehensive analysis of NZSL population dynamics and its relationship to life history. Our model closely predicts the observed trend in population censuses of the main breeding population. We found that the population will continue to decline without effective intervention. Furthermore, we found that the population growth rate is most responsive to changes in survival of adult female NZSLs—the demographic group that is most threatened by fishery bycatch. Nevertheless, inferences about the efficacy of NZSL bycatch reduction measures are still imprecise. Combined, this could explain why the main population of NZSLs continues to decline. Our results emphasise that reliable data on bycatch reduction measures are needed, if they are to be shown to protect key demographic groups of marine mammals.

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Acknowledgments

This work used data from a long-term study approved by the Department of Conservation Animal Ethics Committee (approval AEC86, 1 July, 1999) and funded through the New Zealand Department of Conservation’s Conservation Services Programme. We thank Scott Jarvie, Cláudia Faustino and Anthony Davidson for helpful and critical comments on the manuscript. We thank the University of Otago for funding. Martin Krkošek thanks the Natural Sciences and Engineering Research Council of Canada.

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Correspondence to Stefan Meyer.

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Communicated by G. Pierce.

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227_2015_2695_MOESM1_ESM.pdf

Online Resource A: Model selection on the effect of the breeding status on adult female NZSL survival and recapture 64.0KB

Online Resource B: State and observation process matrices of the CJS model for female NZSLs 140.0KB

Online Resource C (C1 and C2): Posterior distributions of the CJS model for female NZSLs 3.23KB

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Meyer, S., Robertson, B.C., Chilvers, B.L. et al. Population dynamics reveal conservation priorities of the threatened New Zealand sea lion Phocarctos hookeri . Mar Biol 162, 1587–1596 (2015). https://doi.org/10.1007/s00227-015-2695-8

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Keywords

  • Population Growth Rate
  • Adult Survival
  • Crabeater Seal
  • Auckland Island
  • Pinniped Species