Historical and modern distribution and abundance of the New Zealand sea lionPhocarctos hookeri

The benthic-pelagic continuum: Age class and sex differences in the use of the vertical dimension by a rare pinniped

Sea lions as a group, display strong site fidelity, and varying degrees of vulnerability to environmental change, disease and fisheries interactions. One of the rarest pinnipeds, the New Zealand sea lion (NZSL, Phocarctos hookeri) has a very restricted breeding range. At Campbell Island/Motu Ihupuku, one of the two primary breeding sites, at-sea foraging behaviour is unknown. We hypothesised that NZSL of various sex and age classes would utilise the water column differently due to differing physiological constraints and therefore have different accessibility to prey resources. We tested whether sea lion diving behaviour varied in relation to (i) age and sex class, (ii) time of day and (iii) water depth. We also hypothesised that the proportion of benthic/pelagic diving, and consequently risk of fisheries interaction, would vary in relation to age and sex. Satellite telemetry tags were deployed on 25 NZSL from a range of age/sex classes recording dive depth, duration and location. Adult females and juveniles used inshore, benthic habitats, while sub-adult males also utilised benthic habitats, they predominantly used pelagic habitat at greater distances from the island. Adult females and juveniles exhibited shorter dives than the same age/sex classes at the Auckland Islands, suggesting a lower dive effort for these age/sex classes at Campbell Island/Motu Ihupuku. Adult females dived more frequently than other age/sex classes, likely operating closer to their physiological limits; however, further data for this age class is needed. Sub-adult male use of pelagic prey may increase their exposure to mid-water trawls; however, further research detailing the degree of spatial overlap with fisheries is required. This study highlights the utility of spatially explicit dive data to predict vertical habitat use, niche separation of various age and sex classes of marine predators and attribute potential fisheries interaction risk in relation to predator habitat use.

A new extralimital sighting of Monachusmonachus (Hermann, 1779) in the Aquatina di Frigole NATURA 2000 site (IT9150003) beach (Salento peninsula, Apulia Region, Italy) after two decades: strategies for conservation are needed

The Mediterranean monk seal Monachusmonachus (Hermann, 1779) is the most endangered pinniped in the world. In addition, its presence has not been documented for about two decades in the Apulian Region and about 10 years along the Italian coastline. In this work, we aim to describe an exceptional and well-documented observation of a subadult specimen of Monachusmonachus occurring during the last days of January 2020 in the Salento peninsula (Apulia Region, Italy) for the first time after two decades of local extinction in the south-western Adriatic Sea.

What do we know about the fossil record of pinnipeds? A historiographical investigation

The fossil record of pinnipeds (seals, fur seals and walruses) is globally distributed, spanning from the late Oligocene to the Holocene. This record shows a complex evolutionary history that could not otherwise be inferred from their extant relatives, including multiple radiations and iterative ecomorphological specializations among different lineages, many of which are extinct. The fossil record of pinnipeds is not uniformly represented in space and time, however, leaving some gaps in our knowledge. We performed a historiographical investigation of the published fossil record of pinnipeds based on the information available in the Paleobiology Database, with the aim to broadly characterize and evaluate it from a taxonomic, geographical and temporal perspective. We identified major trends, strengths and weaknesses of the pinniped fossil record, including potential biases that may affect our interpretations. We found that 39% of the record corresponds to extant taxa, which are essentially from the Pleistocene and Holocene. There is a larger record from the Northern Hemisphere, suggesting biases in sampling and collection effort. The record is not strongly biased by sedimentary outcrop bias. Specifically, for extinct species, nearly half of them are represented by a single occurrence and a large proportion have type specimens consisting of single isolated postcranial elements. While the pinniped fossil record may have adequate temporal and taxonomic coverage, it has a strong geographical bias and its comparability is hindered by the incompleteness of type specimens. These results should be taken into account when addressing patterns of their past diversity, evolutionary history and paleoecology.

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

•

Infectious disease, including tuberculosis, was the most common cause of death.

•

Anthropogenic trauma caused 26% of deaths in mainland sea lions.

•

Trauma inflicted by adult male conspecifics caused 24% of deaths.

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.

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

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.

Septicaemia and meningitis caused by infection of New Zealand sea lion pups with a hypermucoviscous strain of Klebsiella pneumoniae

This study describes a syndrome of neonatal septicemia and meningitis in New Zealand sea lions, caused by a strain of Klebsiella pneumoniae that is phenotypically similar to strains causing environmentally-acquired septicemia and neuro-invasive disease in humans. Between late 2006 and early 2010, 123 pups from the Enderby Island breeding colony died of K. pneumoniae infection, with lesions including fibrinous to fibrinosuppurative meningitis, subdural hemorrhage, septic arthritis, herniation and hemorrhage of the cerebellar vermis, lymphadenitis and cellulitis. This infection was responsible for 58% of observed pup mortality over this time period, with most deaths occurring in the latter part of the breeding season (mid February onwards). The results of this study suggest that the pattern of this disease has changed since it was first described in 2002, when most deaths occurred early in the season (early to mid-January), and that it is an important and consistent cause of pup mortality in this population. In addition, a similar disease syndrome and bacterial strain was diagnosed in a single pup in a fragile recolonizing New Zealand sea lion population on mainland New Zealand, and the potential effect on this population is unknown but could have a negative impact on recolonisation at this site.

Extinction and recolonization of coastal megafauna following human arrival in New Zealand

Extinctions can dramatically reshape biological communities. As a case in point, ancient mass extinction events apparently facilitated dramatic new evolutionary radiations of surviving lineages. However, scientists have yet to fully understand the consequences of more recent biological upheaval, such as the megafaunal extinctions that occurred globally over the past 50 kyr. New Zealand was the world's last large landmass to be colonized by humans, and its exceptional archaeological record documents a vast number of vertebrate extinctions in the immediate aftermath of Polynesian arrival approximately AD 1280. This recently colonized archipelago thus presents an outstanding opportunity to test for rapid biological responses to extinction. Here, we use ancient DNA (aDNA) analysis to show that extinction of an endemic sea lion lineage (Phocarctos spp.) apparently facilitated a subsequent northward range expansion of a previously subantarctic-limited lineage. This finding parallels a similar extinction-replacement event in penguins (Megadyptes spp.). In both cases, an endemic mainland clade was completely eliminated soon after human arrival, and then replaced by a genetically divergent clade from the remote subantarctic region, all within the space of a few centuries. These data suggest that ecological and demographic processes can play a role in constraining lineage distributions, even for highly dispersive species, and highlight the potential for dynamic biological responses to extinction.

Extensive variation at MHC DRB in the New Zealand sea lion (Phocarctos hookeri) provides evidence for balancing selection

Marine mammals are often reported to possess reduced variation of major histocompatibility complex (MHC) genes compared with their terrestrial counterparts. We evaluated diversity at two MHC class II B genes, DQB and DRB, in the New Zealand sea lion (Phocarctos hookeri, NZSL) a species that has suffered high mortality owing to bacterial epizootics, using Sanger sequencing and haplotype reconstruction, together with next-generation sequencing. Despite this species' prolonged history of small population size and highly restricted distribution, we demonstrate extensive diversity at MHC DRB with 26 alleles, whereas MHC DQB is dimorphic. We identify four DRB codons, predicted to be involved in antigen binding, that are evolving under adaptive evolution. Our data suggest diversity at DRB may be maintained by balancing selection, consistent with the role of this locus as an antigen-binding region and the species' recent history of mass mortality during a series of bacterial epizootics. Phylogenetic analyses of DQB and DRB sequences from pinnipeds and other carnivores revealed significant allelic diversity, but little phylogenetic depth or structure among pinniped alleles; thus, we could neither confirm nor refute the possibility of trans-species polymorphism in this group. The phylogenetic pattern observed however, suggests some significant evolutionary constraint on these loci in the recent past, with the pattern consistent with that expected following an epizootic event. These data may help further elucidate some of the genetic factors underlying the unusually high susceptibility to bacterial infection of the threatened NZSL, and help us to better understand the extent and pattern of MHC diversity in pinnipeds.

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.

In the shallow end: diving behaviour of recolonising female New Zealand sea lions (Phocarctos hookeri) around the Otago Peninsula

Female New Zealand sea lions ( Phocarctos hookeri (Gray, 1844)) at the Auckland Islands (remnant populations) are the deepest and longest diving otariids. These remnant populations are found at the margin of the historical range of the species. We hypothesized that diving behaviours of animals in the core of their historical range is less extreme owing to a better marine habitat. All female New Zealand sea lions (n = 13, aged 2–14 years) born on the Otago Peninsula (initial recolonising population) were equipped with time–depth recorders during April and May 2008, 2009, and 2010. The mean dive depth was 20.2 ± 24.5 m and mean dive duration was 1.8 ± 1.1 min, some of the lowest values reported for otariids. Otago female New Zealand sea lions did not exhibit two distinct diving specialisations as reported at the Auckland Islands. Otago adult females exceeded calculated aerobic dive limits in 7.1% of dives compared with 68.7% at the Auckland Islands. The contrasting differences in diving behaviour between Otago and the Auckland Islands suggest that Otago represents a better marine habitat for New Zealand sea lions, with food easily accessible to animals of all ages.

Hookworm infection, anaemia and genetic variability of the New Zealand sea lion

Hookworms are intestinal blood-feeding nematodes that parasitize and cause high levels of mortality in a wide range of mammals, including otariid pinnipeds. Recently, an empirical study showed that inbreeding (assessed by individual measures of multi-locus heterozygosity) is associated with hookworm-related mortality of California sea lions. If inbreeding increases susceptibility to hookworms, effects would expectedly be stronger in small, fragmented populations. We tested this assumption in the New Zealand sea lion, a threatened otariid that has low levels of genetic variability and high hookworm infection rates. Using a panel of 22 microsatellites, we found that average allelic diversity (5.9) and mean heterozygosity (0.72) were higher than expected for a small population with restricted breeding, and we found no evidence of an association between genetic variability and hookworm resistance. However, similar to what was observed for the California sea lion, homozygosity at a single locus explained the occurrence of anaemia and thrombocytopenia in hookworm-infected pups (generalized linear model, F = 11.81, p < 0.001) and the effect was apparently driven by a particular allele (odds ratio = 34.95%; CI: 7.12-162.41; p < 0.00001). Our study offers further evidence that these haematophagus parasites exert selective pressure on otariid blood-clotting processes.

Relict or colonizer? Extinction and range expansion of penguins in southern New Zealand

Recent human expansion into the Pacific initiated a dramatic avian extinction crisis, and surviving taxa are typically interpreted as declining remnants of previously abundant populations. As a case in point, New Zealand's endangered yellow-eyed penguin (Megadyptes antipodes) is widely considered to have been more abundant and widespread in the past. By contrast, our genetic and morphological analyses of prehistoric, historic and modern penguin samples reveal that this species expanded its range to the New Zealand mainland only in the last few hundred years. This range expansion was apparently facilitated by the extinction of M. antipodes' previously unrecognized sister species following Polynesian settlement in New Zealand. Based on combined genetic and morphological data, we describe this new penguin species, the first known to have suffered human-mediated extinction. The range expansion of M. antipodes so soon after the extinction of its sister species supports a historic paradigmatic shift in New Zealand Polynesian culture. Additionally, such a dynamic biological response to human predation reveals a surprising and less recognized potential for species to have benefited from the extinction of their ecologically similar sister taxa and highlights the complexity of large-scale extinction events.

Philopatry and site fidelity of New Zealand sea lions (Phocarctos hookeri)

The New Zealand sea lion (NZ sea lion), Phocarctos hookeri, is New Zealand’s only endemic pinniped, and one of the worlds rarest otariids. It is classified as ‘Threatened’ based primarily on the low number of breeding sites and restricted distribution. In New Zealand, a species listed as ‘threatened’ is required to be managed to allow its recovery and removal from the list within 20 years. For NZ sea lions this is dependant on the establishment of new breeding areas. However, understanding the recolonisation processes for pinnipeds is still in its infancy with factors such as philopatry needing more research to understand individual dispersal and the recolonisation process. This paper presents the first quantitative investigation into the level of site fidelity and philopatry to breeding beaches in NZ sea lions. Data from resights of NZ sea lions marked as pups from the northern Auckland Island breeding area suggest that both site fidelity and philopatry are important characteristics of this species. Our results show that overall: (1) females have a higher resighting rate than males, particularly at natal sites; (2) female non-natal resightings are predominantly restricted to locations within the northern Auckland Island breeding area (an area of ~10 km2), whereas male resightings are more widely dispersed (up to 700 km to NZ mainland); and (3) philopatry occurs for both sexes, but is more predominant in females than males, with males displaying delay related to sexual and social maturity. The colonisation of new breeding habitats rarely occurs when philopatry is strong and population density is low, stable or declining such as seen for NZ sea lions. Therefore, this research indicates that management of NZ sea lions needs to minimise anthropogenic mortality and encourage population growth to maximise density at breeding sites and encourage females to disperse to establish new breeding areas.