Abstract
There is currently limited information on the small, localised populations of Hector’s dolphins in the south-east South Island. Off the coast of Dunedin, Blueskin Bay appears to provide important habitat for one such small subpopulation of Hector’s dolphins. This subpopulation has not been assessed since 2010/11, when it was identified that its low abundance and apparent discreteness from neighbouring populations rendered it vulnerable to extinction. To address the decline of Hector’s dolphins attributed to bycatch in fishing nets, restrictions on commercial fishing within 4 nautical miles of the coast were implemented in 2008. A subsequent lack of assessment of the efficacy of these measures for facilitating growth of Hector’s dolphin populations has presented the opportunity to assess the conservation status of the small Dunedin subpopulation and the extent of its ongoing vulnerability to fisheries threats. My research aimed to update the subpopulation’s abundance estimate, assess its spatial distribution relative to commercial fishing effort, and to quantify habitat use outside the protection area. Using photo-identification capture-recapture techniques, I estimated that the Dunedin subpopulation consisted of 41 individuals (95% CI = 31 – 54) during the summer of 2021. No evidence for population change since 2010/11 was detected, despite the introduction of restrictions on fishing measures within dolphin habitat in 2008. Kernel density estimates
(KDEs) presented evidence of hotspots of dolphin distribution at Warrington and Waikouaiti. KDEs also illustrated the high use of the protection boundary line for commercial setnetting, and indicated ongoing overlap between Hector’s dolphins and commercial fishing effort. Passive acoustic monitoring was used to quantify habitat use at a known hotspot for Hector’s dolphins, and offshore of the current protected area. Hector’s dolphins were detected on 94% of days inshore; highest detections in winter indicated that shallow waters provide critical habitat for these dolphins year-round. Further from shore, detections on 35% of days, the majority of which were outside of summer months, suggest that these dolphins disperse in winter, ranging further offshore. Detections offshore also indicate potential for direct overlap with commercial fisheries on these days. All analyses confirmed that inshore Blueskin Bay, particularly around Warrington and Waikouaiti, is an area of important habitat for the Dunedin subpopulation of Hector’s dolphins. The inherent vulnerability of small populations to extinction highlights the need to take a precautionary approach to the management of Dunedin’s Hector’s dolphins to facilitate future population recovery. This thesis presents suggestions for management of the Dunedin subpopulation, and underlines the importance of localised management of Hector’s dolphin subpopulations along the south-east coast.