First New Zealand fur seal population assessment at the Bounty Islands in 30 years

A common pitfall in wildlife population monitoring is targeting effort towards locations which are easily accessible due to logistical and resource constraints. This can limit nuanced understandings of population dynamics for species which experience varying stressors through space. The only long-term monitoring programmes for New Zealand fur seal (Arctocephalus forsteri) in New Zealand have occurred within central areas of their nationwide range, and colonies in the sub-Antarctic have been particularly neglected. The last population assessment for New Zealand fur seal on the Bounty Islands was in 1994, when ∼21,500 animals were estimated. This population suffers high by-catch rates in commercial fisheries and may be at elevated risk of High Pathogenicity Avian Influenza due to cohabitation with wide-ranging pelagic seabirds. This study uses imagery collected by an unmanned-aerial-vehicle (UAV) to estimate pup abundance in the 2023/24 breeding season from the Main Group of the Bounty Islands. A total of 4,168-4,256 pups (mean ± SD) were manually counted from high resolution orthomosaics, with pups recorded on eight of the 13 islands/rocks assessed. After accounting for pups that may have been obscured from the UAV images, two established population multipliers were adopted to convert pup production estimates into rough total population estimates for the islands assessed, giving estimates of 20,237-20,663 and 20,832-21,271 respectively. While these results are similar to the 1994 estimate, direct comparisons are constrained by differences in methodologies and survey timing. In addition to providing an important new baseline for an understudied New Zealand fur seal population facing multiple threats, this research demonstrates the benefits of UAVs for population monitoring in regions where traditional methods cannot be easily implemented.