Zealand Sea Lions Phocarctos Hookeri Research Articles

Occurrences and activities of New Zealand sea lions Phocarctos hookeri at non-natal Macquarie Island (1965–1980)

ABSTRACT The distribution of New Zealand sea lions is typically localised to New Zealand and its remote subantarctic islands. However, non-resident male sea lions were seen on Macquarie Island, 650 km from their nearest natal islands, in all months of all years from 1965 to 1980. The majority of the apparently opportunistic sightings were at the northern end of the island. Sightings increased from May to a September-October peak that was coincident with the cessation of breeding activities in the sea lions’ natal range and the period when resident gentoo and royal penguins, and fur and elephant seals aggregated for breeding, all of which are now confirmed prey for New Zealand sea lions on Macquarie Island. The long-term effect of predation pressure from New Zealand sea lions on resident species remains unmeasured. After sleeping, interacting with southern elephant seals was a core sea lion activity. Predation on seabirds and interactions with elephant seals increase the risk of cross-species disease transmission.

Whisker stable isotope analysis used for proactive management of recolonising New Zealand sea lion population

New 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 inferred 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.

Integrated SDM database: Enhancing the relevance and utility of species distribution models in conservation management

Abstract Species' ranges are changing at accelerating rates. Species distribution models (SDMs) are powerful tools that help rangers and decision‐makers prepare for reintroductions, range shifts, reductions and/or expansions by predicting habitat suitability across landscapes. Yet, range‐expanding or ‐shifting species in particular face other challenges that traditional SDM procedures cannot quantify, due to large differences between a species' currently occupied range and potential future range. The realism of SDMs is thus lost and not as useful for conservation management in practice. Here, we address these challenges with an extended assessment of habitat suitability through an integrated SDM database (iSDMdb). The iSDMdb is a spatial database of predicted sites in a species' prediction range, derived from SDM results, and is a single spatial feature that contains additional, user‐friendly data fields that synthesise and summarise SDM predictions and uncertainty, human impacts, restoration features, novel preferences in novel spaces and management priorities. To illustrate its utility, we used the endangered New Zealand sea lion Phocarctos hookeri. We consulted with wildlife rangers, decision‐makers and sea lion experts to supplement SDM predictions with additional, more realistic and applicable information for management. Almost half the data fields included in this database resulted from engaging with these end‐users during our study. The SDM found 395 predicted sites. However, the iSDMdb's additional assessments showed that the actual suitability of most sites (90%) was questionable due to human impacts. >50% of sites contained unnatural barriers (fences, grazing grasslands), and 75% of sites had roads located within the species' range of inland movement. Just 5% of the predicted sites were mostly (>80%) protected. Integrating SDM results with supplemental assessments provides a way to address SDM limitations, especially for range‐expanding or ‐shifting species. SDM products for conservation applications have been critiqued for lacking transparency and interpretation support, and ineffectively communicating uncertainty. The iSDMdb addresses these issues and enhances the practical relevance and utility of SDMs for stakeholders, rangers and decision‐makers. We exemplify how to build an iSDMdb using open‐source tools, and how to make diverse, complex assessments more accessible for end‐users.

First report of systemic toxoplasmosis in a New Zealand sea lion (Phocarctos hookeri)

CASE HISTORY: A 1-year-old female New Zealand sea lion (Phocarctos hookeri) was intermittently observed in the Otago region of New Zealand over an 11-month period, always dragging her hind flippers. In December 2012 the sea lion was found dead, after a period of several days being observed to be harassed by male sea lions.PATHOLOGICAL FINDINGS: At gross postmortem examination the sea lion was in moderate body condition with signs of recent bite wounds and bruising. The lungs were dark and poorly inflated. Histological findings included meningoencephalomyelitis, radiculomyelitis of the cauda equina, myocarditis and myositis. Toxoplasmosis gondii organisms were detected histologically and following immunohistochemistry in the brain, spinal cord, spinal nerves and pelvic muscles.MOLECULAR BIOLOGY: Nested PCR analysis and sequencing confirmed the presence of T. gondii DNA in uterine and lung tissue. A variant type II T. gondii genotype was identified using multilocus PCR-restriction fragment length polymorphism analysis.DIAGNOSIS: Systemic toxoplasmosis.CLINICAL RELEVANCE: Infection with T. gondii involving the spinal cord and nerves was the likely cause of the paresis observed in this sea lion before death. Ultimately, death was attributed to crushing and asphyxiation by a male sea lion, presumably predisposed by impaired mobility. Diagnosis of toxoplasmosis in a New Zealand sea lion highlights the possibility that this disease could play a role in morbidity and mortality in this endangered species, particularly in the recently established mainland populations that are close to feline sources of T. gondii oocysts.

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.

Reply to Comment on “Population dynamics reveal conservation priorities of the threatened New Zealand sea lion Phocarctos hookeri” by Middleton and Breen (2016)

Reply to Comment on “Population dynamics reveal conservation priorities of the threatened New Zealand sea lion Phocarctos hookeri” by Middleton and Breen (2016)

Comment on “Population dynamics reveal conservation priorities of the threatened New Zealand sea lion Phocarctos hookeri” by Meyer, Robertson, Chilvers and Krkošek (2015)

Comment on “Population dynamics reveal conservation priorities of the threatened New Zealand sea lion Phocarctos hookeri” by Meyer, Robertson, Chilvers and Krkošek (2015)

Historical population size of the threatened New Zealand sea lion Phocarctos hookeri

Abstract Marine mammal species were exploited worldwide during periods of commercial sealing in the 18th and 19th centuries. For many of these species, an estimate of the pre-exploitation abundance of the species is lacking, as historical catch records are generally scarce and inaccurate. Genetic estimates of long-term effective population size provide a means to estimate the pre-exploitation abundance. Here, we apply genetic methods to estimate the long-term effective population size of the subantarctic lineage of the New Zealand sea lion (NZ sea lion), Phocarctos hookeri . This species is predominantly restricted to the subantarctic islands, south of mainland New Zealand, following commercial sealing in the 19th century. Today, the population consists of ~9,880 animals and population growth is slow. Auckland Island breeding colonies of NZ sea lion are currently impacted by commercial trawl fisheries via regular sea lion deaths as bycatch. In order to estimate sustainable levels of bycatch, an estimate of the population’s carrying capacity ( K ) is required. We apply the genetically estimated long-term effective population size of NZ sea lions as a proxy for the estimated historical carrying capacity of the subantarctic population. The historical abundance of subantarctic NZ sea lions was significantly higher than the target values of K employed by the contemporary management. The current management strategy may allow unsustainable bycatch levels, thereby limiting the recovery of the NZ sea lion population toward historical carrying capacity.

Population dynamics reveal conservation priorities of the threatened New Zealand sea lion Phocarctos hookeri

Understanding the life history basis of the population dynamics of threatened species is crucial to their assessment and recovery. Within the Southern Pacific Ocean, the decline and range contraction of New Zealand sea lions (NZSLs) (Phocarctos hookeri) are an exemplary case of a major fisheries and conservation controversy. Despite the use of bycatch reduction measures, the main population of the NZSL has declined since 1998 and its vulnerability to threats is poorly understood. Here we develop a population model for the declining population of the endangered NZSL at the Auckland Islands, New Zealand (\(50^{\circ }30^{\prime }\hbox {S}, 166^{\circ }17^{\prime }\hbox {E}\)), parameterised by mark-recapture data of 2928 female NZSLs spanning 15 years from 1998 to 2012, and provide the first comprehensive analysis of NZSL population dynamics and its relationship to life history. Our model closely predicts the observed trend in population censuses of the main breeding population. We found that the population will continue to decline without effective intervention. Furthermore, we found that the population growth rate is most responsive to changes in survival of adult female NZSLs—the demographic group that is most threatened by fishery bycatch. Nevertheless, inferences about the efficacy of NZSL bycatch reduction measures are still imprecise. Combined, this could explain why the main population of NZSLs continues to decline. Our results emphasise that reliable data on bycatch reduction measures are needed, if they are to be shown to protect key demographic groups of marine mammals.

Diet of New Zealand sea lions (Phocarctos hookeri) at their southern breeding limits

The New Zealand (NZ) sea lion (Phocarctos hookeri) is endemic to NZ and is listed as “Vulnerable” by the International Union for Conservation of Nature. Approximately 99 % of pups are born at the Auckland Islands (a declining population) and Campbell Island (a growing population). The causes of contrasting population trajectory are not well understood, though spatial and temporal variations in prey availability have frequently been implicated for other pinnipeds. This is the first published diet study of the Campbell Island population, located at the species’ southern breeding limit. Prey species were identified and quantified from scats and regurgitate samples collected in March 2013 (n = 159 and 7, respectively). An array of prey taxa was identified, though two species were particularly dominant in terms of reconstituted diet mass (M) of fishes and cephalopods: small-scaled cod (Notothenia microlepidota), which dominated scat samples (50 % M); and yellow octopus (Enteroctopus zealandicus), which dominated a small sample of regurgitates (72 % M). The diet lacked many of the key prey taxa of the Auckland Islands, and we hypothesise that the key prey identified here provides a highly available food source for the growing population of NZ sea lions at Campbell Island. These differences are likely to reflect spatial heterogeneity in prey availability and may be one of the main causes of an increase in NZ sea lion population size at Campbell Island in contrast to a decrease at the Auckland Islands.

Long-term survival and reproductive success of New Zealand sea lions (Phocarctos hookeri) treated with ivermectin as pups

Context Hookworms (Uncinaria spp.) are a common parasite of neonatal fur seals and sea lions around the world and may contribute to decreased pup growth and survival. Removal of these parasitic burdens by administration of the anthelmintic ivermectin has been trialled in New Zealand (NZ) sea lion (Phocarctos hookeri) pups at Sandy Bay, Enderby Island, with initial benefits in growth and survival reported. Long-term effects, however, are not known. Aims To determine the impact of ivermectin treatment administered in the first month of life, on long-term survival and fecundity in a sample of NZ sea lion pups. Methods For a sample of treated and control pups born between 2002 and 2004, resighting data to 2012 was assessed with the Cox proportional hazards analysis to evaluate survival to maturity and fecundity. Key results Sample size was a limiting factor as juvenile survival was very low, but a trend of improved survival was observed in the ivermectin-treated group. Year of birth was significant due to the effects of a bacterial epizootic in the first year of the trial. Reproductive rate was not significantly different between groups. Conclusions The effect of disease and parasitism on the survival of NZ sea lions is apparent, contributing to early pup mortality, with potentially wider-ranging implications for juvenile survival and beyond. Implications Further research is warranted to investigate anthelmintic treatment of NZ sea lion pups as a safe and effective management tool to improve survival and recruitment in declining populations.

Is management limiting the recovery of the New Zealand sea lion Phocarctos hookeri?

Pup production of the ‘nationally critical’ New Zealand sea lion Phocarctos hookeri has declined by 48 % since 1998, with fisheries bycatch playing a role in this decline. Current management of the sea lion population involves, amongst other measures, the setting of an annual bycatch limit based on Bayesian modelling of the sea lion population and fisheries information. Success of management scenarios is determined against two criteria, both of which involve keeping the sea lion population at or above 90 % of a modelled carrying capacity (6,987 mature individuals). Due to a lack of information on the pre-sealing abundance of the New Zealand sea lion, it is unclear whether the modelled carrying capacity represents a cap on sea lion recovery. Here, I use published estimates of genetic diversity based on microsatellite loci (expected heterozygosity, He) of the New Zealand sea lion and other otariid species to estimate historical effective population size (Ne). I then use existing knowledge of the ratio of Ne to census population size (NC) to determine a historical census population size of these species. Genetical estimates of historical Ne suggest that NZ sea lions were considerably more abundant (>68,000 individuals) historically than the current population estimate (11,855 animals). Importantly, the genetical estimate of historical population size suggests that the modelled carrying capacity (6,987 mature sea lions) is likely an underestimation of recovery potential of the species; hence, current management maybe limiting the recovery of the species.

Foraging diversity in lactating New Zealand sea lions: insights from qualitative and quantitative fatty acid analysis

Lactating New Zealand (NZ) sea lions (Phocarctos hookeri) exhibit different foraging patterns during their foraging trips, with benthic divers spending more energy at sea than mesopelagic conspecifics. We compared blubber fatty acids (FAs) of 14 benthic and 12 mesopelagic females captured at the Auckland Islands, NZ subantarctic, in late January 2000 using an analysis of similarities (ANOSIM). FA profiles between foraging types were significantly different (global R = 0.30, p = 0.001), suggesting a different use in prey resources. We then compared the diet predictions by quantitative FA signature analysis (QFASA) by using a prey FA library available in the region. Overall, diet predictions were significantly distinct between benthic and mesopelagic females (global R = 0.17, p = 0.022), although the diets consisted of the same prey but in different contributions. The results suggest benthic females do not compensate their higher foraging costs by feeding on prey with higher energy densities. Foraging areas of benthic females are not exploited by the trawling fishery; therefore, the benthic tactic might be a trade-off between a higher foraging cost and less resource competition.

Contrast in the importance of arrow squid as prey of male New Zealand sea lions and New Zealand fur seals at The Snares, subantarctic New Zealand

New Zealand sea lions (Phocarctos hookeri) are threatened by incidental bycatch in the trawl fishery for southern arrow squid (Nototodarus sloanii). An overlap between the fishery and foraging sea lions has previously been interpreted as one piece of evidence supporting resource competition for squid. However, there is currently no consensus about the importance of squid in the diet of New Zealand sea lions. Therefore, we investigated this importance independently of spatial and temporal differences in squid availability through a simultaneous study with sympatric New Zealand fur seals (Arctocephalus forsteri), a species known to target arrow squid. Diet sampling at The Snares (48°01′S 166°32′E), subantarctic New Zealand, in February 2012 coincided with peak annual catch in the nearby squid fishery. Diets were deduced by analyses of diagnostic prey remains from scats (faeces) and casts (regurgitations). The contribution of each prey species to the diet was quantified using the per cent index of relative importance (% IRI) that combined frequency of occurrence, mass and number of prey items. Arrow squid was a minor component in sea lion scats (2 % IRI), and none was found in their casts. In contrast, arrow squid was the major component in fur seal scats and casts (93 and 99 % IRI, respectively). This study found that New Zealand sea lions ate minimal squid at a time when squid was clearly available as evidenced by the diet of New Zealand fur seals; hence, there was no indication of resource competition between sea lions and the squid fishery.

Pre-human New Zealand sea lion (Phocarctos hookeri) rookeries on mainland New Zealand

Holocene New Zealand sea lion (Phocarctos hookeri) bones collected from the north of New Zealand's South Island strengthen existing evidence for the former Holocene presence of breeding colonies of P. hookeri on mainland New Zealand. The taxonomic identity of Phocarctos bones is confirmed using both morphology and ancient DNA analysis. Five radiocarbon dates on four adult and one pup bone from Creighton's Cave near Paturau, northwest Nelson, ranged from 1290±30 yr BP to 5430±30 yr BP. Three radiocarbon dates on pup bones spanning 200 14C yr (1550±30 yr BP to 1390±30 yr BP) reveal that a prehistoric breeding rookery was present at Delaware Bay, Nelson, until shortly before the time of human arrival c. AD 1280 (670 yr BP). The Delaware Bay site in particular provides a valuable ‘snapshot’ of coastal New Zealand faunas shortly before human arrival, one that has potential to enhance our understanding of changes in the endemic coastal fauna associated with human colonisation.

Importance of studying foraging site fidelity for spatial conservation measures in a mobile predator

The efficiency of spatial conservation measures for threatened species depends mostly on the proportion of time that animals spend within the protected areas. We illustrate this with our case study of the population of recolonizing female New Zealand (NZ) sea lions Phocarctos hookeri (n = 13) at Otago Peninsula, South Island, NZ. Human interactions at sea, where sea lions forage, are of concern, and spatial management measures have been proposed. Understanding the level of foraging site fidelity of these animals was consequently essential. We used satellite tracking of individuals across three autumns to assess foraging site fidelity and year-round on-land sighting surveys over 2.5 years as proxy to foraging areas outside autumns. Each individual exhibited a high level of autumnal site fidelity for foraging areas between years (64% overlap between 65% Kernel ranges with a 3-km buffer) while using beaches along a 12-km stretch of coastline during 96 ± 8% (range 79–100%) of their time onshore. As a proxy for foraging areas outside autumns, these animals exhibited a high level of site fidelity to this stretch of coastline throughout the year. Breeding females were sighted there during 86% of months (range = 73–100%) and non-breeding females during 69% of months (range = 58–90%). The site fidelity of these animals indicates that protected areas would be efficient in this case and highlights the importance of studying foraging site fidelity in mobile predators to design efficient conservation measures.

Foraging Behaviour of Juvenile Female New Zealand Sea Lions (Phocarctos hookeri) in Contrasting Environments

Foragers can show adaptive responses to changes within their environment through morphological and behavioural plasticity. We investigated the plasticity in body size, at sea movements and diving behaviour of juvenile female New Zealand (NZ) sea lions (Phocarctos hookeri) in two contrasting environments. The NZ sea lion is one of the rarest pinnipeds in the world. Most of the species is based at the subantarctic Auckland Islands (AI; considered to be marginal foraging habitat), with a recolonizing population on the Otago Peninsula, NZ mainland (considered to be more optimal habitat). We investigated how juvenile NZ sea lions adjust their foraging behaviour in contrasting environments by deploying satellite-linked platform transmitting terminals (PTTs) and time-depth recorders (TDRs) on 2–3 year-old females at AI (2007–2010) and Otago (2009–2010). Juvenile female NZ sea lions exhibited plasticity in body size and behaviour. Otago juveniles were significantly heavier than AI juveniles. Linear mixed effects models showed that study site had the most important effect on foraging behaviour, while mass and age had little influence. AI juveniles spent more time at sea, foraged over larger areas, and dove deeper and longer than Otago juveniles. It is difficult to attribute a specific cause to the observed contrasts in foraging behaviour because these differences may be driven by disparities in habitat/prey characteristics, conspecific density levels or interseasonal variation. Nevertheless, the smaller size and increased foraging effort of AI juveniles, combined with the lower productivity in this region, support the hypothesis that AI are less optimal habitat than Otago. It is more difficult for juveniles to forage in suboptimal habitats given their restricted foraging ability and lower tolerance for food limitation compared to adults. Thus, effective management measures should consider the impacts of low resource environments, along with changes that can alter food availability such as potential resource competition with fisheries.

Mass and bathymetry influences on the foraging behaviour of dependent yearling New Zealand sea lions (Phocarctos hookeri)

Juvenile foraging ability is limited due to physiological and morphological constraints. Restricted foraging skills can result in reduced juvenile survival, which can lead to population decline. Given the important role mass plays in influencing foraging behaviour and survival, we deployed satellite-linked time-depth recorders (TDRs) on seven dependent yearling New Zealand sea lions (Phocarctos hookeri) over three seasons from 2008–2010 at the New Zealand subantarctic Auckland Islands to study how mass influenced at sea movements and diving behaviour. Mass was significantly negatively related to dive depth and descent rate, indicating yearling diving behaviour may be influenced by their mass. The yearlings demonstrated inter-individual variation in foraging locations and strategies. This individual variation was likely attributed to the bathymetry of different foraging areas dictating possible dive depths. Thus, when studying foraging behaviour, in addition to physiological and morphological influences, researchers must examine external factors such as the physical characteristics of the foraging habitat.

Body regional distribution and stratification of fatty acids in the blubber of New Zealand sea lions: implications for diet predictions

Fatty acids (FAs) from blubber are often analysed to assess the diet of marine mammals. However, distribution of blubber FAs is not necessarily uniform along the body. It is therefore important to understand the deposition of dietary fat to be able to estimate the diet. We analysed the FA compositions of the thoracic ventral (T region) blubber of 28 New Zealand (NZ) sea lions Phocarctos hookeri by-caught by the southern arrow squid Nototodarus sloani fishery. Each blubber sample was divided into an inner and an outer layer. For 16 of these 28 animals, the pelvic dorsal (P) region was also sampled. The influence of body region and layer was statistically tested on the distribution of blubber FAs. We found minimal differences between the P and T regions (3 out of 29 FAs). The outer blubber layer was more concentrated in short-chain monounsaturated FAs, and less concentrated in saturated FAs, but the degree of stratification was small. Diet predictions from quantitative FA signature analysis (QFASA) applied on different body regions were similar. When applied to different blubber layers, QFASA gave some variation in the contribution of rattails (~25 % in outer blubber vs. ~12 % in inner blubber). Nonetheless, diet predicted from both layers was dominated by similar prey species: octopus, hoki and rattails. Hoki and rattails shared a similar ecological niche. Therefore, feeding ecology of NZ sea lions inferred from the inner or the outer blubber would lead to the same conclusions. In the case of NZ sea lions, the outer layer of blubber, if the only sample accessible, could be a useful tissue for diet inference from FAs.

Using life‐history traits of New Zealand sea lions, Auckland Islands to clarify potential causes of decline

AbstractAnnual censuses of New Zealand (NZ) sea lions Phocarctos hookeri at the subantarctic Auckland Islands have indicated a decline in pup production of over 40% during the first decade of the 2000s. With this significant decline and likely decline in the population as a whole, population ecology theory hypothesizes that life‐history traits such as reproduction rate, survival or growth should improve, particularly if density‐dependency is playing a significant role in the population. This research examined whether changes in NZ sea lion pup production were associated with changes in adult abundance or population life‐history traits in an attempt to clarify potential causes of decline. Since 1998/1999, daily surveys of Sandy Bay, Enderby Island, were undertaken during the NZ sea lion breeding season (December–February). These surveys confirm that the number of adults at the breeding area has significantly declined during the period of pup production decline. There was no difference between years in mean pup birth date, but the ratio of pups to females ashore during peak pupping varied significantly. The sex ratio of pups at birth also varied from year to year, but with no significant variation overall. Pup mortality varied significantly only during years of epizootic events (1997/1998, 2001/2002 and 2002/2003). Pup birth mass showed little variation between 2000/2001 and 2006/2007, increasing slightly in the last 3 years of study. Pup mass at 3 weeks, although highly variable, showed no trend during the period of decline. Despite the significant decrease in pup production and breeding animals, not all life‐history traits relating to pup mass and survival or female fecundity improved. Research suggests that indirect fishing‐related pressures may influence some of these traits and that the NZ sea lion population was unlikely to have been influenced by density‐dependent factors or to have been at or near carrying capacity before the decline.