Polar Biol DOI 10.1007/s00300-011-1143-6ORIGINAL PAPER Population viability analysis of New Zealand sea lions, Auckland Islands, New Zealand’s sub-Antarctics: assessing relative impacts

Abstract A common issue faced in wildlife management is how to assess the uncertainty of potential impacts on the viability of a species or population. The pup production of New Zealand (NZ) sea lions (Phocarctos hookeri) has declined 50 % in the last 12 years at their main breeding area, the Auckland Islands. The two major known atypical impacts on NZ sea lions are as follows: (1) the direct mor-tality as bycatch of trawling and (2) bacterial epizootics, which can aVect reproduction and mortality. Both of these impacts include high levels of uncertainty, with Wsheries data being variable due to percentage observer coverage and the eVect of sea lion exclusion devises, while the tim-ing and severity of bacterial epizootics are not predictable. In this paper, an age-structured model of the NZ sea lion population at the Auckland Islands was built to examine the predicted eVects of Wsheries mortality and catastrophes (bacterial epizootics), both separately and then combined, on population viability over a 100-year period using the VORTEX population viability analysis programme. These models are then compared against 15 years of empirical Weld data to determine the actual level of impacts being observed. Model results indicate that although naturally occurring epizootics reduce the growth rate of the popula-tion, it does not cause a decline in the Auckland Island pop-ulation. However, sustained Wsheries bycatch at current estimated levels, particularly considering its potential impact on adult female survival, could result in a popula-tion decline and possible functional extinction over the modelled time period