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Item Stable isotope analysis of New Zealand sea lion (Phocarctos hookeri) whiskers shows distinct regional ecological niches(Elsevier BV, Amsterdam, 2025-10-01) Chilvers BL; Galbraith DA region's isoscape (isotopic values within a marine ecosystem) can vary markedly, providing the ability to assess the foraging and migration behaviours of apex marine predators through stable isotope analysis of inert tissue such as whiskers. Additionally, these values can be used to determine the area of origin. The New Zealand sea lion (Phocarctos hookeri) breeds over 7 degrees of latitude from Otago Peninsula (45.8°S), South Island, New Zealand, to Campbell Island (52.5°S), a 750 km distance. For most of their range, there is incomplete description of their foraging ecology and diet. We analysed δ13C and δ15N stable isotope ratios from pup whiskers (n = 160) from the five main breeding areas, across three distinct regions for New Zealand sea lions. We investigated isotopic niches for each breeding area to give insight into foraging behaviours and determined whether isotopic values could be used to identify the place of origin of individuals. We found significant differences in isotopic values between the five breeding areas except Enderby and Dundas Islands, Auckland Islands. The differences between breeding areas are likely driven by a combination of prey abundance, distribution and consumption by the pups' mothers, underlying oceanographic variability, varying isotopic baselines, and potential impacts from human influences. Isotopic niche widths were greatest in the Auckland Islands region. This research highlights the value of stable isotope analysis to investigate regional scale variations of apex marine predators foraging and could provide insight into anthropogenic and environmental factors that could influence resource useItem Whisker stable isotope analysis used for proactive management of recolonising New Zealand sea lion population(Inter-Research Science Publisher, 2023-10-26) Chilvers BLNew Zealand sea lions Phocarctos hookeri have experienced a 46% decline in pup production in the last 25 yr, driven by female deaths in trawl fisheries around the Auckland Islands. The only colony for this species recorded away from the subantarctics and this fishing impact is on Stewart Island. Despite the Stewart Island colony only being 1% of the species, it is significant, as it is currently the only stable population and is located in an area away from most on-land human impacts, although not away from potential fisheries pressures. To ensure this colony’s persistence, more information is needed on these sea lions’ diet, foraging behaviour, and local fisheries interactions for management that promotes their protection. The present research investigates the long-term foraging behaviour, and infers the diet, of female New Zealand sea lions on Stewart Island using their known foraging behaviour and linking this to their proximal and full-length whisker stable isotope values. Previous foraging studies found that these animals have small foraging areas with consistent mesopelagic diving behaviours. These behaviours, linked with their whisker stable isotope values, show consistency in foraging behaviour and in - ferred diet across their entire adult life. Currently, there are no known commercial fisheries bycatch issues for sea lions around Stewart Island. However, precautionary measures ensuring fisheries pressure does not increase and management to safeguard that deepwater trawling and finfish aquaculture remain absent would be proactive steps that should be undertaken for the protection of this new colony and for this Endangered species as a whole.