Journal Articles
Permanent URI for this collectionhttps://mro.massey.ac.nz/handle/10179/7915
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Item Reasons for admission and post-release survival of UK rehabilitated herring gulls (Larus argentatus) from 1999 to 2024(Cambridge University Press, 2025-10-22) Thompson R; Chilvers BL; Stenning MJGlobally, millions of animals transition through wildlife rehabilitation facilities annually. Data recorded at these facilities can be used to quantitatively assess factors which result in the animals’ admittance, treatment, release, and survival, and how impacts such as high pathogen avian influenza (HPAI) has altered these parameters. Twenty-five years of records of herring gull (Larus argentatus) admittances into RSPCA Mallydams Wood Wildlife Rehabilitation Centre, Hastings, UK (between 1999 and 2024) were reviewed to determine admission factors and their impacts on the number of days in care and the likelihood of release. Additionally, for the years 1999 to 2010, data were collected on days of post-release survival and distances from the centre travelled from ringed and released birds. During that 25-year period, 17,334 herring gulls were admitted into the Mallydams Centre with 9,013 released, and 2,796 ringed and released between 1999 and 2010. Release rates varied significantly with the category of problem identified at admission. Wild nesting herring gulls, even without the impact of HPAI, have been declining throughout the UK, and the additional anthropogenic pressures on urban gull populations have resulted in a documented national decline in the species. Rehabilitating and returning birds to the wild has shown to be important both for their animal welfare and population, as well as helping identify the impact of HPAI on local urban populations of all relevant species. Results from this research can be utilised to adapt training and resources at rehabilitation centres and determine euthanasia protocols to optimise animal welfare along with release and survival success.Item Larger foraging area means greater fisheries interaction risk for juvenile yellow-eyed penguins in their sub-Antarctic range(Springer-Verlag GmbH, 2025-12-01) Muller CG; Chilvers BL; French RK; Battley PFSeabird foraging success is crucial for individual survival and therefore also for recruitment, breeding success, and population stability. However, there is limited information on the movements of juvenile seabirds, including penguins. This study investigates the foraging range of juvenile yellow-eyed penguins from Enderby Island, in the sub-Antarctic Auckland Islands, and their overlap with protected areas where commercial fishing is prohibited. Two juvenile penguins were tracked using GPS-Argos tags, and their movements were compared to those of breeding adults. Juveniles travelled up to 275.2 km from the colony, significantly farther than the maximum 46.7 km for breeding adults. Juveniles also used a much larger foraging area of 18,027 km2, compared to 738 km2 for adults. Only 7% of juvenile foraging occurred within the protected area, highlighting their potential vulnerability to commercial fishing activities. Juveniles had a 17% overlap with commercial fishing areas, compared to 4% for adults. The extensive foraging range and low overlap with protected areas suggest that juveniles are at higher risk of encountering threats, which may contribute to higher mortality rates. These findings underscore the need for conservation efforts to investigate and address threats in the broader foraging areas used by juveniles. Future research should track additional juvenile penguins and study prey availability to support effective conservation strategies for this endangered species.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 Using Stable Isotopes to Assign Origin of White-Chinned Petrels Killed by Longline Fisheries(John Wiley and Sons Ltd, 2025-07-08) Barquete V; Cherel Y; Phillips RA; Thompson D; Chilvers BL; Wanless RM; Ryan PGIncidental capture (bycatch) of seabirds in longline and trawl fisheries is one of the main threats to many albatrosses and large petrels. The White-chinned Petrel (Procellaria aequinoctialis) has a circumpolar distribution and is the seabird species killed most frequently by fisheries in the Southern Ocean. In an attempt to identify provenance, stable isotope values (δ13C and δ15N) in feathers from White-chinned Petrels killed in longline fisheries off Brazil, South Africa and New Zealand were compared with those from petrels breeding at five major colonies (South Georgia, Prince Edward, Crozet, Kerguelen and Antipodes Islands). Feather δ15N, and to a lesser extent, δ13C values in feathers differed among breeding birds sampled at South Georgia, Antipodes Islands and the three Indian Ocean colonies. Given that adult feathers are moulted primarily in temperate waters, away from their colonies, this confirms that most adults from these three regions winter in different areas. Discriminant function analysis of stable isotope values indicated that most petrels killed off Brazil and South Africa were from Atlantic and Indian Ocean populations, respectively. Birds killed in New Zealand fisheries in summer were assigned to populations from all three oceans, with few assigned to the Antipodes; however, we lacked stable isotope data from the Auckland Islands, which is the most likely source population. Identifying the origin of bycaught birds is essential for determining which populations are affected by human activities and for prioritising conservation efforts. This includes targeting of mitigation regulations, monitoring of compliance and bycatch rates, and ensuring cooperation between breeding and non-breeding range states to ensure best practices are adopted in national fisheries and in the high seas.Item Establishment of a stable isotope database for New Zealand fur seal breeding colonies using δ13C and δ15N in pup vibrissae(Taylor and Francis Group on behalf of the Royal Society of New Zealand, 2025-05-21) Galbraith D; Chilvers BL; Bilgmann KThe New Zealand fur seal/kekeno (Arctocephalus forsteri, NZFS) is native to Aotearoa/New Zealand. Its original range included the entire coast of mainland New Zealand, and offshore and subantarctic islands. The NZFS has gradually recolonised much of its former range after being almost extirpated by hunting, however, little is known about species dispersal in the non-breeding season. Stable isotope analysis (SIA) can trace foraging ecology and migration in marine mammal species. Isotopic niche width can be described statistically and provides ecologically relevant information on diet and potentially foraging location. Otariid pup vibrissae (whiskers) can be used as proxies for maternal foraging as they provide a sequential record of nutrient intake derived from maternal milk. In this study, vibrissae from NZFS pups were collected from seven established breeding areas around the coast of New Zealand. A stable isotope database of δ13C and δ15N was established for each breeding colony, and isotopic niche widths estimated. Isotopic niche widths were largest at Open Bay Islands and Cape Foulwind. Results were discussed in light of previous oceanographic and NZFS diet and foraging studies. Colonies are not likely to be sufficiently isotopically distinct for pups to be identified to their colony of origin.Item Towards an Abundance Estimate for New Zealand Fur Seal in New Zealand(John Wiley and Sons Ltd, Hoboken, USA, 2025-04) Hall A; Chilvers BL; Weir JS; Burdett HA lack of population abundance and trajectory data is a conservation and management issue relevant to numerous pinniped species, many of which are exposed to a variety of threats. New Zealand fur seal (Arctocephalus forsteri; ‘NZFS’) populations in different parts of New Zealand have experienced both substantial increases and decreases to their abundance over the last 50 years, since the last nationwide census. Here, existing data and stage-structured matrix modelling were used to provide a contemporary nationwide estimate of NZFS abundance. Graphical depictions demonstrate the spatial inconsistencies in NZFS monitoring in New Zealand through time. A minimum population estimate of 131,338–168,269 NZFS was calculated by combining the most recently available pup production data from around New Zealand and using established multipliers. A second estimate of 181,646–239,473 NZFS was calculated using stage-structured matrix models to project contemporary abundance. Inconsistent NZFS population monitoring and sparse vital rate data for New Zealand's NZFS limited this study, and both population ranges are likely underestimates. However, they still represent substantial increases on the most cited nationwide abundance figure (100,000 NZFS). From these findings, we suggest that a regularised program of monitoring is adopted for New Zealand's NZFS, as has been achieved for similar species in other countries. This would both aid in the management of NZFS in the face of emerging risks, such as H5N1 avian influenza, and enable their use as a sentinel for the health of New Zealand's marine ecosystems.Item Planning for a pinniped response during a marine oil spill(Springer-Verlag GmbH, 2025-04-04) Hall AA; Chilvers BL; Weir JS; Garrigues PUnderstanding the distribution and abundance of wildlife populations is key to successful oil spill response planning. Fur seals are difficult to rehabilitate if oiled, and many common spill response techniques may be limited in the high-energy rocky shore habitats they prefer. Preventing oil from reaching colonies, and hazing or deterring animals away from oil are high-priority response options for pinnipeds during spills. To do this, local knowledge of pinniped distribution and abundance is required, as well as knowledge of effective and safe hazing and deterrence mechanisms. From pup production assessments, we estimated that a population of 13,147–17,675 New Zealand fur seal (NZFS: Arctocephalus forsteri) currently inhabits Banks Peninsula. This area contains the largest port on New Zealand’s South Island and a secondary port that is popular with cruise ships, elevating its oil spill risk profile. From the knowledge gained regarding NZFS distribution and abundance, we evaluated mitigation methods which could protect fur seals during oil spills, wherever these species occur, and make suggestions to managers on how to mount an effective pinniped response.Item Variable breeding success and its implication in the conservation of endangered yellow-eyed penguin (Megadyptes antipodes) at the New Zealand subantarctic Auckland Islands(John Wiley and Sons, Inc., 2024-04-19) Muller CG; Chilvers BL; French RK; Battley PFKnowledge of breeding success is essential for conservation, as it is required for monitoring populations and survival trends. Seabird reproductive success can be negatively affected by prey availability, marine-based stochasticity, extreme weather events, individual breeders' performance and direct threats such as disease, predation and fisheries interactions. The endangered yellow-eyed penguin (Megadyptes antipodes) is declining in mainland New Zealand, however, little is known about its breeding success in the subantarctic where the majority of the species breeds. Yellow-eyed penguin breeding success data were collected from a total of 167 nests on subantarctic Enderby Island, Auckland Islands, New Zealand, from the 2015 to 2017 breeding seasons. This included egg and chick mortality and fledging rates, plus a wider sample of the fledgling condition of 276 chicks. Fledging success was higher than in mainland New Zealand in some years, although chicks were smaller and lighter on average, highlighting the need for more information on juvenile survival probabilities in the subantarctic. Breeding success measures were similar in 2015 and 2016, but a large egg mortality in 2017 caused a significant reduction in breeding success that year. Such variability requires more investigation into the correlates of breeding success, including possible stressors such as foraging success, adverse weather and environmental effects, and pathogens. These results demonstrate the need for ongoing monitoring of yellow-eyed penguin breeding success across the subantarctic in order to establish baselines for normal variation and to determine whether anthropogenic (manageable) factors may be contributing to low productivity. This research highlights an important consideration for endangered species conservation; that breeding success may not be consistent over time, or across a species' entire range. Additional monitoring of all breeding populations should be carried out to ensure up-to-date information is available to inform conservation management decisions for the species.Item 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.Item Earthquake impacts on a protected pinniped in New Zealand(John Wiley and Sons, Inc., 2024-01-03) Hall AA; Chilvers BL; Weir JS; Boren LJThe impacts of natural disasters on marine mammals are poorly understood and difficult to study, which can hamper management responses following such events. This study provides the first distribution and abundance assessment of New Zealand fur seal (NZFS: Arctocephalus forsteri) colonies around Kaikōura, New Zealand, since a 7.8 magnitude earthquake in November 2016 caused substantial changes to both the local marine and terrestrial environments, and led to the reconstruction of a major highway that runs adjacent to NZFS colonies. Mark–recapture and direct counts in the 2022–2023 breeding season estimated pup production for NZFS breeding colonies along the Kaikōura coast. Using established multipliers, pup estimates were used to provide the first comprehensive population estimate for Kaikōura's NZFS population since the earthquake. Three new colonies and three new subcolonies were assessed and recorded, additional to reassessments of two established colonies. Overall, Kaikōura's NZFS population has grown and spread post-earthquake, with an upper total population estimate of between 21,560 and 28,327 animals in the 2022–2023 breeding season. Some sites, such as Lynch's Reef, appear to have benefited from earthquake-induced coastal uplift, with pup production increasing. Contrastingly, the estimated 2,401 (±99) pups produced at Ōhau Point in 2023 is similar to pre-earthquake estimates. This indicates that the earthquake has disrupted previously documented growth at this site. The distribution of NZFS breeding at Ōhau Point has also changed substantially since the last pre-earthquake assessment. From these findings, alterations to the Ōhau Point New Zealand Fur Seal Sanctuary and similar protections at other locations on the Kaikōura coast are suggested, as greater numbers of NZFSs are now accessible to human interaction and disturbance. The results demonstrate both how natural disasters and subsequent infrastructure modifications can impact coastal species and how conservation measures may need to be amended accordingly.