Home ranges and diving behavior of endangered New Zealand sea lions along the Catlins coast of South Island, New Zealand
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New Zealand sea lions (Phocarctos hookeri) were extirpated from the North and South Islands of New Zealand during pre-European native hunting, and their numbers were greatly reduced on the Auckland and Campbell Islands during European commercial sealing. However, they began reoccupying South Island in 1994, and pup production remains low but steady. The home range, at-sea movements, and diving behavior of females at the breeding colony along the Catlins Coast of South Island have not been studied since its inception in 2006. The goal of the study was to: 1) evaluate the performance of home range models to identify the most accurate model(s) for a semi-aquatic distribution, 2) track movements to identify home ranges, and 3) record diving behavior of females to characterize foraging behavior and estimate energy expenditure. To accomplish this study, we attached satellite telemeters and video and data recorders to females along the Catlins Coast during austral winter of 2019. Home ranges were most accurately modeled by separating inshore and offshore habitats and applying adaptive local convex hulls (LOCOH) and fixed kernel density with plug-in bandwidth selection (PKDE), respectively. This method minimized the ranges outside of used habitat, handled boundaries to movement, and performed accurately in cross-validation evaluation. The results showed the importance of home range model selection. Total home ranges were small and restricted to coastal areas. Foraging cycles were frequent, with short times at sea and onshore. Dives were shallow, short in duration, and divided into three types based on variables derived from three-dimensional dive analysis. Dive characteristics indicated a benthic foraging strategy with transit periods between foraging patches. At-sea estimated metabolic rate varied by activity, with an estimated field metabolic rate lower than that of females at the Auckland Islands, possibly indicating differences in energetic expenditure among populations. It appears that females along the Catlins Coast consume nearshore, abundant prey and require less time and smaller home ranges for foraging compared to that for females in the Auckland Islands. Although reoccupation of their historic range on South Island will take decades, suitable habitat for breeding and prey availability along the southeast coast are encouraging.
