Enderby Island Research Articles

The age and position of the southern boundary of prehistoric Polynesian dispersal

AbstractPrehistoric Polynesian voyaging into high latitudes with landfall in Antarctica remains a widely credited proposition. We examine it through archaeological and environmental evidence from the Subantarctic region of the southwest Pacific, focussing upon an extensive archaeological site at Sandy Bay on Enderby Island. Combining a new set of radiocarbon ages with former, older, ages we show that the site is now within the same rapid expansion phase in which South Polynesia was first colonised. Radiocarbon ages across the site indicate a single continuous settlement, probably of some decades. Consideration of limiting factors in Subantarctic settlement, including of seafaring capability and critical resources, suggests that the site was about as far south as prehistoric habitation could be sustained and was probably vacated at the onset of the Little Ice age (LIA) in the late 14th century. An absence of prehistoric remains on islands further south also suggests that Polynesian exploration reached a boundary 2000 km short of Antarctica. The southern case is discussed briefly in the wider context of Polynesian expansion.

Variable breeding success and its implication in the conservation of endangered yellow‐eyed penguin (Megadyptes antipodes) at the New Zealand subantarctic Auckland Islands

Abstract Knowledge 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.

PREVALENCE AND PATHOGEN LOAD OF EIMERIA IN WILD YELLOW-EYED PENGUINS (MEGADYPTES ANTIPODES) AND THE MORPHOLOGIC CHARACTERIZATION OF A NOVEL EIMERIA SPECIES.

Coccidia infections in wild birds rarely cause clinical signs; however, disease and mortality can occur with predisposing environmental and host conditions. The Yellow-eyed Penguin (Megadyptes antipodes) is an endangered species endemic to New Zealand that has seen significant ongoing population decline. The aim of this study was to examine the host-pathogen dynamics of coccidian parasites in two wild populations of Yellow-eyed Penguin: the mainland (South Island) population and the sub-Antarctic (Enderby Island) population. There was weak evidence for a difference in the prevalence of the Eimeria sp. in birds from Enderby Island (76.6%; 36/47; 95% confidence interval [CI] 62.78-86.4%) and the South Island of New Zealand (58.54%; 24/41; 95% CI 43.37-72.24%). The mean pathogen load in penguins on Enderby Island was 9,723 oocysts/g of feces (SE=5831 oocysts/g) and from the South Island of New Zealand was 1,050 oocysts/g (SE=398 oocysts/g). No evidence of an association was found between pathogen load and body weight in either study population. The morphology of the sporulated coccidial oocysts was consistent with a novel species of Eimeria. There was statistically significant variation between the oocysts collected from the two sites in all measurements apart from the oocyst wall thickness. However, the standard technique of assessing linear regressions of the length and width of oocysts from both sampling sites was 0.80, and therefore above the standard R2>0.5 used to indicate variation within a single population of oocysts, suggesting that only a single species of Eimeria was present at both sampling locations. The prevalence and pathogen load of Eimeria sp. was substantially higher than previous reports of coccidial oocysts in Yellow-eyed Penguins and free-living Sphenisciformes globally. This host-parasite relationship deserves further investigation, as the impact of this novel organism on the population remains unclear.

The eradication of cattle from Enderby Island and subsequent ecological response

Cattle (Bos taurus) were liberated on 695 ha Enderby Island, the northernmost of the Auckland Island group, in 1894–96, after a previous liberation had died out. After reaching a peak population of c. 100 animals, they established a relatively stable population of 35–60 animals for the latter half of the 20th century.

The eradication of cattle from Enderby Island and subsequent ecological response

The eradication of cattle from Enderby Island and subsequent ecological response

Diet plasticity and links to changing foraging behaviour in the conservation of subantarctic yellow‐eyed penguins (Megadyptes antipodes)

Abstract Diet is a key factor affecting seabird foraging behaviour, ultimately influencing survival, breeding success and long‐term population viability. The density and distribution of prey species in the marine environment are influenced by many factors including climate effects such as El Niño southern oscillation and climate change that alter water temperature. While poor quality diet has been implicated as a contributing factor in the decline of some mainland New Zealand yellow‐eyed penguin (Megadyptes antipodes) populations, little is known about their diet in the subantarctic where the majority of the species breeds. Blood and feather samples (n = 63) were collected for stable isotope analysis of diet from 25 individual birds breeding on subantarctic Enderby Island, Auckland Islands, New Zealand, from 2015 to 2018. Diet data were analysed by factors such as breeding year, sex and foraging behaviour. Stable isotope analysis demonstrated significant changes in diet during each year of the study, which included both El Niño and La Niña conditions. Diet during El Niño conditions comprised lower trophic level prey, which were more benthic, and found closer to shore than diet during La Niña. Coupled with the reported variable breeding success of yellow‐eyed penguins in the subantarctic, variable diet suggests prey availability is likely to be a limiting factor in some years. Prey availability is therefore expected to be a major influence on survival and breeding success of this endangered species in the future, particularly if the effects of climate change become more pronounced. This research highlights an urgent conservation need to identify prey species utilized by the southern population, along with their distribution in time and space, and therefore also the effect of diet on long‐term population stability.

Clinical parameters of hypervirulent Klebsiella pneumoniae disease and ivermectin treatment in New Zealand sea lion (Phocarctos hookeri) pups.

Hypervirulent Klebsiella pneumoniae infection causes significant mortality of endangered New Zealand sea lion pups at Enderby Island, Auckland Islands. Gross necropsy and histopathology findings are well reported, but little is known about the clinical course of disease in affected pups. To determine factors feasible as clinical screening tools for hypervirulent K. pneumoniae in live pups, 150 pups over two field seasons (2016–18) were recruited shortly after birth for a prospective cohort study. A randomised controlled clinical treatment trial with the anthelmintic ivermectin was conducted concurrently and risk factor data and biological samples were collected approximately fortnightly. Treatment with ivermectin has been demonstrated to reduce the risk of hypervirulent K. pneumoniae mortality in pups, so effects on clinical parameters between the treated and control cohorts were also investigated. A broader sample of pups were monitored for clinical signs to investigate the course of disease in affected pups. Clinical signs, haematology and oral and rectal swabs to detect gastrointestinal carriage of hypervirulent K. pneumoniae were not useful for detection of disease prior to death. Of those pups that died due to hypervirulent K. pneumoniae, only 26.1% (18/69) had any clinical signs prior, likely a reflection of the peracute course of disease. On comparison of haematological parameters between ivermectin-treated and control pups, significantly lower total plasma protein and higher eosinophil counts were seen in control versus treated pups, however standard length as a surrogate for age was a more important influence on parameters overall than ivermectin treatment. This study also highlighted a cohort of pups with severe clinical signs suggestive of hypervirulent K. pneumoniae infection were lost to follow up at the end of the monitored season, which could be contributing to cryptic juvenile mortality.

Risk Factors for New Zealand Sea Lion (Phocarctos hookeri) Pup Mortality: Ivermectin Improves Survival for Conservation Management

Septicaemia due to hypervirulent (HV) Klebsiella pneumoniae is the leading cause of neonatal pup mortality in endangered New Zealand sea lions (Phocarctos hookeri) at Enderby Island, in the New Zealand sub-Antarctic. Accounting for approximately 60% of annual pup mortality at this site following an epizootic event in 2001–02, HV K. pneumoniae is also emerging worldwide as a significant community-acquired human pathogen. To facilitate efficient direct mitigation to reduce pup mortality, a case-control study and prospective cohort study were conducted to identify risk factors amenable to active management. Additionally, to investigate impacts of hookworm (Uncinaria spp.), a nested treatment trial with the anthelmintic ivermectin was undertaken concurrently. During two austral summer field seasons (2016–2018), 698 pups were captured for treatment trial recruitment and the collection of morphometric measurements, biological samples and risk factor data. Gastrointestinal carriage of the virulent phenotype of K. pneumoniae was a consistent risk factor, while ivermectin treatment and higher body condition index consistently reduced risk of HV K. pneumoniae mortality. Significantly fewer ivermectin-treated pups were found dead (24.1% control, 11.1% treatment), with a trend towards a higher proportion of HV K. pneumoniae deaths amongst the control group. This study provides evidence to support ivermectin treatment as a pup mortality mitigation strategy in New Zealand sea lions at Enderby Island. If applied to larger colonies where HV K. pneumoniae and hookworm impact pup survival, this intervention could have population-scale benefits for this endangered species. Further work is required to understand how ivermectin prevents HV K. pneumoniae septicaemia, but removal of hookworms before intestinal mucosal damage occurs could limit systemic spread of virulent bacteria from the gastrointestinal tract.

Foraging areas and plasticity of yellow-eyed penguins Megadyptes antipodes in their subantarctic range

Foraging behaviour is crucial to breeding success for marine predators, including seabirds. Yellow-eyed penguins Megadyptes antipodes are central-place, predominantly benthic foragers around mainland New Zealand. The northern (mainland) population of this Endangered species is declining, with changes in the marine environment a suspected cause, particularly warming water and poorer foraging success. We undertook a detailed foraging study of the data-deficient subantarctic population, which is distinct from the northern population. Over 2 breeding seasons, we collected 91 GPS foraging logs from 69 breeding yellow-eyed penguins from Enderby Island, Auckland Islands, New Zealand. The mean foraging distance was 24 km from shore (max 47 km). Foraging area size was greater for females and for pelagic foragers, although benthic foragers travelled further from shore on average. Diving plasticity was evident both in diving behaviour and foraging area use. Foraging area and distance from shore were greater for all birds in a year of greater breeding effort and fledging success (2016). Foraging occurred over continental shelf waters, similar to the mainland, and in areas up to 150 m deep, so any differences in foraging behaviour compared to those reported for the northern population are likely influenced by local bathymetry, environmental conditions, and individual preference. Despite comparable bathymetry in some areas, the southern population showed greater foraging plasticity, with 62% of foraging trips categorised as pelagic, implying that subantarctic foraging conditions may differ from the predominantly benthic mainland foraging. Variable foraging conditions may therefore have implications for future breeding success in the subantarctic.

Extreme diving of females at the largest colony of New Zealand sea lions, Phocarctos hookeri

The diving behaviours of marine predators are thought to be coupled with species demographics. Species that forage at or close to their physiological limits will be limited in their ability to respond to natural or anthropogenic induced changes in their environment. This is the case for the New Zealand sea lion (Phocarctos hookeri). A previous study from Enderby Island, Auckland Islands, the third largest colony for the endangered species, showed lactating females exhibit extreme diving behaviour, and that individuals have either: a benthic diving ecotype or a deeper, more varied mesopelagic diving ecotype which are maintained throughout their adult life. The ecological significance and implications for individual foraging specialisation has major consequences for this species as mesopelagic foragers are more likely to suffer mortality from fisheries than benthic foragers. We investigated the diving behaviour of lactating females from Dundas Island, Auckland Islands, the largest breeding colony for New Zealand sea lions. The diving behaviour of 24 lactating females was examined and confirmed that both diving ecotypes exist and that females at this colony are also operating at the upper limit of their physiological capability. Enderby and Dundas Island are the largest breeding colonies for the New Zealand sea lion and together represent 69% of this species pup production. This population has significantly declined since 1998, predominantly due to direct and indirect fisheries interactions. Measurable conservation and management steps are therefore critical to mitigate the impacts of fisheries on this population.

Diving plasticity in the ancestral range of the yellow-eyed penguin Megadyptes antipodes, an endangered marine predator

In long-lived marine predators such as penguins, foraging behaviour is related to breeding success. Yellow-eyed penguins Megadyptes antipodes are thought to be predominantly benthic foragers around mainland New Zealand, with previous dive studies showing little variation in diving behaviour and minimal change by year or breeding status. This apparent absence of foraging flexibility may be linked to local prey availability and therefore also to foraging success, factors believed to contribute to the current population decline. Here, we undertook the first detailed study of yellow-eyed penguin diving and foraging behaviour in the subantarctic Auckland Islands, part of the original ancestral range of the species that colonised mainland New Zealand. We collected dive logs from 134 foraging trips made by 73 breeders from Enderby Island, Auckland Islands, in the New Zealand subantarctic. Pelagic dives and foraging trips were recorded in the subantarctic population—a foraging strategy not previously published in dive studies on this species. Changes between benthic and pelagic foraging were recorded for individuals within foraging trips, within a breeding season, and between years. Differences in diving behaviour between the subantarctic and that reported for mainland New Zealand are likely influenced by local bathymetry and environmental conditions, and prey availability. However, the subantarctic population shows a greater use of pelagic foraging not evident in the northern population, even in areas that have a similar depth to some mainland foraging areas. This observed foraging flexibility may have implications for breeding success and potentially the long-term population trends of these 2 genetically similar populations.

Rare great hammerhead predation of a wedgefish

Many species of sharks are apex predators, exerting top-down control on coral reef communities via predation and behavioral modification of prey. The great hammerhead (Sphyrna mokarran) is broadly distributed in tropical waters, with a varied diet composed of crustaceans, cephalopods, bony fish, and other elasmobranchs. Gut-content analysis has indicated a preference for rays and skates, including larger taxa such as guitarfish; however, direct observations of predation are rarely witnessed. At noon on 7 Nov 2019, we observed a large great hammerhead shark (~3.5–4 m total length) preying on a bottlenose wedgefish (Rhynchobatus australiae) (~2–2.5 m total length) at a depth of 2.5 m in a shallow bay off Enderby Island (top photo), in the Dampier Archipelago, along the north coast of Western Australia. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

Pup mortality in New Zealand sea lions (Phocarctos hookeri) at Enderby Island, Auckland Islands, 2013-18.

New Zealand sea lions (Phocarctos hookeri) are an endemic and endangered species. Pup mortality at Enderby Island (50.5°S, 166.28°E) in the New Zealand sub-Antarctic has been well studied, with subsequent investigations yielding more intricate detail of the causes of mortality, as new diagnostic methods become available. Klebsiella pneumoniae was first reported in 2001–02 at this site, causing a pup mortality epizootic and is now known to be present at several colonies. This bacterium is a common mucosal commensal of humans and animals, however the agent found in pups at necropsy is a hypervirulent strain, readily recognised in microbial culture as being hypermucoviscous. Infection causes septicaemia with a common syndrome of subsequent meningitis and polyarthritis. This investigation uses histopathology and microbiology, with new modalities such as matrix assisted laser desorption/ionisation—time of flight mass spectrometry to show that Klebsiella septicaemia could have historically been, and continues to be, the most important cause of pup mortality, but has been previously underrepresented due to the often cryptic presentation and sometimes peracute course of disease. Hypermucoviscous K. pneumoniae should be considered a serious threat to pup survival in the species, causing on average 60.2% of pup deaths annually at Enderby Island between 2013 and 2018, with likely more continuing mortality following pup dispersal and the cessation of the summer monitoring season. Less common causes of death included starvation (14.8%), trauma/asphyxiation (9.9%) and other infections (7%). This study forms the basis for further evaluation of risk factors for pup mortality in the species, with a view to developing active mitigation.

Causes of adult mortality in two populations of New Zealand sea lions (Phocarctos hookeri)

The New Zealand sea lion is an endangered species endemic to New Zealand. While causes of death are well described for pups of this species, mortality in adults is poorly characterised. This study investigated causes of death in 136 New Zealand sea lions in two different populations: a major breeding site on remote, uninhabited Enderby Island in the sub-Antarctic, and a slowly increasing recolonising population on the inhabited mainland. For animals with at least a partial diagnostic investigation (n = 112), the most frequently diagnosed causes of mortality were infectious disease (41/112; 37%), particularly tuberculosis due to M. pinnipedii (20/112; 18%), and conspecific trauma (27/112; 24%). Anthropogenic trauma was an important cause of death in mainland sea lions (9/33; 26%). Deliberate anthropogenic mortality has previously been identified as the greatest potential threat to population recovery for mainland sea lions, and as human and pinniped populations increase, managing interactions between these species will become increasingly important.

Aerial VHF tracking of wildlife using an unmanned aerial vehicle (UAV): comparing efficiency of yellow-eyed penguin (Megadyptes antipodes) nest location methods

Context Locating cryptic animals is an important aspect of many wildlife management programs and research studies. However, this process can be inefficient, time-consuming and expensive. Unmanned aerial vehicles (UAVs), unmanned aircraft systems (UASs) or drones fitted with a camera are increasingly being used for counting and monitoring wildlife; however, these are often not suitable for cryptic species. Very high-frequency (VHF) radio-tracking is commonplace; however, single-channel VHF receivers mean that animals must be tracked individually, or scanning receivers must be used; but this raises the possibility of signals being missed. Aims We aimed to test the effectiveness of aerial VHF tracking using a multi-channel receiver for locating wildlife. Methods We tracked wildlife fitted with VHF transmitters operating on individual frequencies, by means of a UAV with a multi-channel VHF receiver to simultaneously monitor all frequencies. This offered distinct advantages over traditional single-channel scanning receivers. To test and compare this novel method, yellow-eyed penguins (Megadyptes antipodes) were located on nests hidden under vegetation on Enderby Island in the New Zealand subantarctic, using manual ground searching, unassisted ground VHF tracking, as well as using location flights by the UAV Drone Ranger system. Key results The UAV system allowed for faster nest location than did all other methods, with a higher cumulative success (number of nests found each day) and lower search effort required (person hours per nest). Conclusions Aerial VHF tracking can greatly extend the search range and minimise search effort compared with ground VHF tracking or manual searching. Implications This technology has applications for locating and tracking a wide range of wildlife, particularly cryptic species that may be difficult to find using other methods.

Behavioural consequences of human disturbance on subantarctic Yellow-eyed Penguins Megadyptes antipodes

SummaryHuman disturbance can have behavioural, physiological and population-level consequences on wildlife. Unregulated tourism is having a negative effect on the endangered Yellow-eyed Penguin Megadyptes antipodes on mainland New Zealand. Subantarctic Yellow-eyed Penguins are exposed to tourism on Enderby Island in the Auckland Islands group, 450 km south of New Zealand. Restrictions and guidelines for tourism are in place on Enderby Island, but there has been little study on the efficacy of these. We quantified behavioural responses of the Yellow-eyed Penguin on Enderby Island to human presence by documenting movement patterns and behaviour of penguins in the presence and absence of humans, through both controlled approaches and monitoring penguin behaviour in the presence of tourists. We used these data to model the effective approach distances for reducing disturbance. Human presence caused a significant drop in the probability of a successful transit to or from their nest, and significantly increased the time penguins spent alert and decreased the time spent preening. Modelling showed the distance from a human to a penguin is a significant predictor of the likelihood of a bird displaying disturbance behaviour, with the current minimum approach guideline of 5 m not sufficient for preventing disturbance. Our results indicate that the minimum approach guideline needs to be revised if the probability of disturbance is to be reduced. Modelling the appropriateness of minimum approach guidelines by predicting the probability of disturbance is a useful technique that could be applied to other species and systems. Worldwide, management guidelines need to be scientifically evaluated to ensure efficacy and cater for the more sensitive species affected.

Pathology and Epidemiology of Stillbirth in New Zealand Sea Lions (Phocarctos hookeri) From Enderby Island, Auckland Islands, 1998-2012.

Stillbirth is a small and often cryptic fraction of neonatal mortality in mammals including pinnipeds. As part of an investigation into the poor reproductive success of the endangered New Zealand sea lion (Phocarctos hookeri), archived tissues from 37 stillborn pups born on Enderby Island between 1998 and 2012 were examined using histopathological techniques. Apart from bronchopneumonia with neutrophilic infiltration in 4 cases, few inflammatory conditions were identified in stillborn pups. However, 27/32 (84%) stillborn pups had aspirated squames present in the respiratory tract, without meconium. It is unclear if this finding represents fetal distress during parturition or whether it is a normal finding for this species. Three pups lacked histological evidence of hepatic glycogen storage, which may indicate placental defects or maternal undernutrition. No evidence of infectious disease was found on histopathological analysis, consistent with the low seroprevalence in New Zealand of infections known to cause reproductive failure in other pinniped species. This study forms an important baseline for further examination of stillborn New Zealand sea lion pups, as pup mortality is investigated as a contributor to the species' decline.

Seroprevalence of Toxoplasma gondii in mainland and sub-Antarctic New Zealand sea lion (Phocarctos hookeri) populations

AIMS: To investigate the seroprevalence of antibodies to Toxoplasma gondii in New Zealand sea lions (Phocarctos hookeri), as a potential contributor to reproductive failure.METHODS: Archived sera were sourced from New Zealand sea lions from two recolonising mainland populations in the Otago Peninsula (n=15) and Stewart Island (n=12), as well as a declining population at Enderby Island (n=28) in the New Zealand sub-Antarctic. Sera were tested for antibodies to T. gondii using a commercially available ELISA (with samples considered positive if the sample to positive ratio was >30%), and latex agglutination test (LAT; with titres ≥1:32 considered positive). Western blot analysis was used to validate the results of a subset of 14 samples.RESULTS: Five samples from sea lions in mainland locations were confirmed positive for antibodies to T. gondii. Two adult females exhibited high LAT antibody titres (min 1:2048, max 1:4096) on both occasions when sampled 1 and 2 years apart, respectively. No animals from Enderby Island were seropositive.CONCLUSIONS: Toxoplasma gondii infection is unlikely to be a major contributor to poor reproductive success in New Zealand sea lions. However, continued surveillance is pertinent to assess subclinical and clinical impacts of the parasite on these threatened populations. The commercial tests evaluated here, with further species-specific threshold refinement could provide a fast, inexpensive and reliable indicator of T. gondii exposure in New Zealand sea lions.

Palaeoecological signatures of vegetation change induced by herbivory regime shifts on subantarctic Enderby Island

The stratigraphic relationships of palaeoecological proxies and use of changepoint analyses to determine the cause and effect relationships between past events has allowed a better understanding of the relative contributions of humans and environmental drivers to Late Quaternary extinctions and of their effects on terrestrial ecosystems. Few studies, however, have validated these approaches at localities where past interactions between vegetation communities and large herbivores are well-documented. Here, we use a peat core from subantarctic Enderby Island to present the first study tracing the spores of dung fungi alongside pollen at a site where the history of mammalian herbivore introductions (and subsequent eradication), and their effects on the vegetation, are precisely known. We find a strong connection between spore influx rates of the dung-fungus Sporormiella and PCA axis 1 of the pollen assemblages, suggesting that past vegetation change caused by herbivore introductions and eradications at the core site can be readily deduced from the palaeoecological record. The response of the vegetation community to the removal of herbivores was so rapid, however, that a difference in timing between changepoints relating to specific pollen taxa, the overall pollen community, and the decline of Sporormiella spores, could not be resolved in our record, despite a sampling resolution of <5 years. We suggest that further case-studies, spanning different vegetation and herbivore communities, are required to provide increased confidence in inferences drawn about cause-and-effect relationships using proxy changepoint offsets in palaeoecological records.

Comparison of breeding population survey methods for the Auckland Island shag (Phalacrocorax colensoi)

The Auckland Island shag (Phalacrocorax colensoi) is endemic to New Zealand and restricted to the subantarctic Auckland Islands. The species is classified as “Vulnerable” under the New Zealand threat classification systems. The total breeding population is estimated at <1000 pairs, with Enderby Island considered to be the stronghold for the species. The trend of the population is unknown, and it has been recommended a census of the entire adult population be conducted once a suitable methodology has been developed. The objective of this research was to examine census methods to estimate population size for the Auckland Island shag. Three census methods were trialled on Enderby Island during the 2011/2012 breeding season: (a) boat-based counts; (b) aerial photography using a helicopter and; (c) direct counts from the ground. The aerial photographic survey recorded 1889 pairs of Auckland Island shags breeding on Enderby Island during the 2011/2012 breeding season. In comparison, boat-based and ground count surveys recorded lower population sizes by 27 and 26 %, respectively. This research provides the first comparable methodology and baseline population estimate for the breeding stronghold of this threatened seabird and forms the basis for long-term population monitoring. All methodologies examined here could be used for other cliff-nesting seabird species; however, these results indicate a level of bias may be present for any survey method.