NZ sea lion pup count at the Auckland Islands 2021/22

Published:  

September 2022
This is the final report for POP2018-03 New Zealand sea lion: Auckland Islands pup count.

Summary

This report summarises fieldwork undertaken as part of Conservation Services Programme (CSP) project POP2018-03 ‘New Zealand sea lion: Auckland Islands pup count’ by the Department of Conservation. All scheduled New Zealand sea lion Threat Management Plan (TMP) fieldwork for the subantarctic islands was cancelled for the 2021/22 field season.

Five days of CSP fieldwork were completed on the Auckland Islands, from 6 to 10 January 2022, which allowed for mark-recapture estimates and direct counts of sea lion pups on Enderby, Dundas, and Figure of Eight Islands. However, the timing of the research was c. 10 days earlier than standardised counts due to vessel availability, and, therefore, not all pups had been born when counts occurred. Additional tasks, including incidental tag resightings, direct colony counts, and assessment of alternative materials for mark-recapture marking of pups were undertaken.

Total pup production for the Auckland Islands was estimated at 1686 ± 51.4 pups (mean ± 1SE), which includes an adjustment to account for the early date of the counts, and 43 pups found dead at the time of counts. This figure is approximately 1.9% higher than the sum of mean direct counts and mark-recapture estimates without adjustment (minimum estimate = 1617 ± 49.4 pups). Both the adjusted and minimum estimates were higher than the minimum target of 1575 pups set in the New Zealand sea lion Threat Management Plan (DOC and MPI 2017), and both are considered to be underestimates of this year’s pup production, due to the lack of cumulative dead pup count data from Enderby and the use of direct count methods (rather than mark-recapture) on Dundas Island.

Based on these estimates, Auckland Islands pup production has remained stable since 2009. Management actions to improve pup survival, which might improve population growth, including terrain trap mitigation and Ivermectin treatment, have not been achieved in the last three years. In addition, the last three seasons have not delivered the fieldwork necessary to support a robust analysis of pup and female survival, including pup morphometrics, flipper tagging and transponder insertion, and structured daily resighting effort for tagged animals. To this end, while the five-year objective to ‘halt the decline’ of the New Zealand sea lion has been achieved because pup production 6 DOC-6944966 numbers have not dipped below site-specific measures of success, without continued animal marking and resighting of marked individuals there will be significant data deficiency which will limit our ability to analyse demographic trends and effectiveness of interventions.

There are an increasing number of challenges to conducting work on New Zealand’s subantarctic islands, particularly with respect to COVID-19 and public health restrictions, vessel availability and cost, and the ongoing commitment to improving health and safety systems for remote island work. It is imperative that a full season of subantarctic fieldwork be conducted in 2022/23 so that New Zealand sea lion population and demographic research, as well as interventions to improve survival of pups, can be implemented and assessed.

Publication information

Young MJ and Manno K (2022). Auckland Islands 2021/22 New Zealand sea lion field research report: Conservation Services Programme pup count. Department of Conservation, Dunedin. 35 pp.

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