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Is management limiting the recovery of the New Zealand sea lion Phocarctos hookeri?

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Abstract

Pup production of the ‘nationally critical’ New Zealand sea lion Phocarctos hookeri has declined by 48 % since 1998, with fisheries bycatch playing a role in this decline. Current management of the sea lion population involves, amongst other measures, the setting of an annual bycatch limit based on Bayesian modelling of the sea lion population and fisheries information. Success of management scenarios is determined against two criteria, both of which involve keeping the sea lion population at or above 90 % of a modelled carrying capacity (6,987 mature individuals). Due to a lack of information on the pre-sealing abundance of the New Zealand sea lion, it is unclear whether the modelled carrying capacity represents a cap on sea lion recovery. Here, I use published estimates of genetic diversity based on microsatellite loci (expected heterozygosity, H e) of the New Zealand sea lion and other otariid species to estimate historical effective population size (N e). I then use existing knowledge of the ratio of N e to census population size (N C) to determine a historical census population size of these species. Genetical estimates of historical N e suggest that NZ sea lions were considerably more abundant (>68,000 individuals) historically than the current population estimate (11,855 animals). Importantly, the genetical estimate of historical population size suggests that the modelled carrying capacity (6,987 mature sea lions) is likely an underestimation of recovery potential of the species; hence, current management maybe limiting the recovery of the species.

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Acknowledgments

I thank Amelie Auge, Catherine Collins, Nicolas Dussex, Catherine Grueber and Fiona Robertson for helpful discussion and three reviewers for helpful comments on the manuscript. This research was supported by funding from the New Zealand Department of Conservation (Grant No. 4219) and Department of Zoology, University of Otago.

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  1. Department of Zoology, Allan Wilson Centre for Molecular Ecology and Evolution, University of Otago, PO Box 56, Dunedin, 9054, New Zealand

    Bruce C. Robertson

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  1. Bruce C. Robertson
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Correspondence to Bruce C. Robertson.

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Robertson, B.C. Is management limiting the recovery of the New Zealand sea lion Phocarctos hookeri?. Polar Biol 38, 539–546 (2015). https://doi.org/10.1007/s00300-014-1619-2

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