Leopard seals (Hydrurga leptonyx) occur mainly south of the Antarctic Polar Front, but immatures, in particular, seasonally move beyond this range during the austral winter and spring, typically under increased sea ice conditions. Extralimital occurrences of leopard seals can be observed at several sub-Antarctic islands where they haul out to rest. We present new records of leopard seal sightings at Marion Island, southern Indian Ocean, from 2006 to 2024 and discuss fluctuations in their seasonal and annual abundance (drawing on data collected since 1980) and body condition based on regular surveys. The eastern beaches at Marion Island were surveyed every 7–10 days while the western beaches were visited monthly. Observed leopard seals were photographed and given a body condition score based on the visibility of bony protrusions. From 2006 to 2024, we identified 35 presumed unique immature leopard seals between July and November, with a peak in September, all being immatures. Individuals to which we could assign body condition scores were either in good or excellent condition. This contrasted with the prevailing hypothesis that leopard seal body condition deteriorates with decreasing latitude. However, we could not determine whether this was because of an actual shift in body condition or because we used a different scoring system from other studies. We recommend adopting a standardised scoring system for visually estimating pinniped body condition and a global repository to monitor leopard seal haul-outs. As an apex predator, leopard seals may be important indicators in Antarctic and sub-Antarctic ecosystems, and monitoring changes in their distribution and body condition may indicate environmental and biological changes in these remote regions.

Identifying important demographic drivers of population dynamics is fundamental for understanding life-history evolution and implementing effective conservation measures. Integrated population models (IPMs) coupled with transient life table response experiments (tLTREs) allow ecologists to quantify the contributions of demographic parameters to observed population change. While IPMs can estimate parameters that are not estimable using any data source alone, for example, immigration, the estimated contribution of such parameters to population change is prone to bias. Currently, it is unclear when robust conclusions can be drawn from them. We sought to understand the drivers of a rebounding southern elephant seal population on Marion Island using the IPM-tLTRE framework, applied to count and mark-recapture data on 9500 female seals over nearly 40 years. Given the uncertainty around IPM-tLTRE estimates of immigration, we also aimed to investigate the utility of simulation and sensitivity analyses as general tools for evaluating the robustness of conclusions obtained in this framework. Using a Bayesian IPM and tLTRE analysis, we quantified the contributions of survival, immigration and population structure to population growth. We assessed the sensitivity of our estimates to choice of multivariate priors on immigration and other vital rates. To do so we make a novel application of Gaussian process priors, in comparison with commonly used shrinkage priors. Using simulation, we assessed our model's ability to estimate the demographic contribution of immigration under different levels of temporal variance in immigration. The tLTRE analysis suggested that adult survival and immigration were the most important drivers of recent population growth. While the contribution of immigration was sensitive to prior choices, the estimate was consistently large. Furthermore, our simulation study validated the importance of immigration by showing that our estimate of its demographic contribution is unlikely to result as a biased overestimate. Our results highlight the connectivity between distant populations of southern elephant seals, illustrating that female dispersal can be important in regulating the abundance of local populations even when natal site fidelity is high. More generally, we demonstrate how robust ecological conclusions may be obtained about immigration from the IPM-tLTRE framework, by combining sensitivity analysis and simulation. This in-depth study considers the contribution of immigration to population growth, when immigration is estimated indirectly in an integrated population model. The authors demonstrate the importance of simulation and sensitivity analysis for obtaining robust conclusions, and introduce an elegant prior to the problem along the way.image

We analysed unpublished data on territory size and tenure in adult male sub-Antarctic fur seals Arctocephalus tropicalis recorded at Gough Island, Southern Ocean, during the 1975/76 austral summer breeding season. Adult males (n=15) remained on their territories for between 35–56 days (mean 45.4±6.7 days). Territory size during the peak breeding season was 21.9 m2 on average (n=42), but when partitioned by beach type, average territory sizes were 13.8 (n=9), 20.1 (n=17) and 28.3 m2 (n=16). Both territory tenure and territory size fall within the reported range of values established in fur seal species which hold territories on land as the predominant male reproductive strategy. We highlight numerous confounding factors that impact comparative studies which should be considered when interpreting theoretical, conceptual, and modelling approaches about territorial behaviour in otariids.

The first year of life is critical for large mammals to acquire foraging and predator avoidance skills. Southern elephant seal (Mirounga leonina) pups wean at approximately three weeks of age and depart on their first foraging trips in midsummer, typically remaining at sea for three to four months before returning to their natal islands. We describe the foraging trips (n = 29) of 16 underyearling southern elephant seals from sub-Antarctic Marion Island and compare these with trips (n = 152) of 94 older seals from the same population. While subadults (prebreeding age) and adult females (breeding age) displayed directional travel, underyearlings traveled in multiple directions from the island with no evidence of repeatability of travel directions within or between individuals and years. Maiden trips took longer to complete than subsequent trips during the first year of life, but we found no evidence for significant changes in other track metrics between the first three foraging trips. The comparatively inconsistent movement patterns of underyearlings suggest that foraging strategies of individuals are influenced by their learning and/or success during the first year of life and that individual level consistency in successful foraging strategies only become apparent in subsequent years.

We recorded intra-sexual behaviour of adult male sub-Antarctic fur seals Arctocephalus tropicalis at Gough Island, Southern Ocean, during the 1975/76 summer breeding season. Our re-analysed data address male ‘contest competition’, which relates to the costs of intra-sexual disputes, including fights. We considered the risks/benefits of fighting through investigation of injuries ( n = 353) sustained by adult males ( n = 124) in fights. Injuries were predominantly on the forequarters, especially around the insertion areas of the front flippers (41%) with its sparse pelage, compared to the neck and chest areas combined (29%), an area which is well protected by thick pelage. The infliction of serious, sometimes debilitating, injuries to competitors increases a male’s access to females. Injuries predominate in injured, defeated males that gather at non-breeding sites, suggesting that injuries inflicted by dominant males were successful in excluding competing males from breeding sites.

This study presents the pattern of occurrence of sub-Antarctic fur seals (SAFS), Arctocephalus tropicalis , in the southern Brazilian coast and evaluate its association with climatic variability and anomalies in the concentration of chlorophytes and sea surface temperature in the reproductive colonies of Gough and Tristan da Cunha Islands. Date, sex, and age class of 254 stranded SAFS recorded between 1992 and 2013 were analyzed. Representative indexes of the patterns of climatic variability and environmental variables were obtained between four and five months before the records, the assumed interval of displacement for species between their closest breeding colonies and the southern Brazilian coast. The species was observed in southern Brazil between May and November each year, and most individuals were adult males. The records of SAFS on the southern Brazilian coast were associated with low concentration of chlorophytes interacting with negative sea surface temperature anomalies, and positive events of South Annular Mode, South Atlantic Ocean Dipole and Indian Ocean Dipole. Climatic variability is influencing the ecology SAFS, because it affects the environmental factors, that act as a driver of dispersion of the species. These variables had been interacting together in the region of the breeding colonies, and possibly during the fur seals’ journey towards the Brazilian coast. Considering the current scenario of global climate change, we expect that SAFS will continue to disperse to areas beyond their regular distribution, not only in the direction of the coasts of southern continents, but also further south, towards higher latitudes.

Polygynous males allocate substantial resources to sexual traits and behaviours to improve their chances of winning competitions for mates often at the cost of body maintenance. However, the degree to which males experience these trade-offs can be influenced by external conditions. Studies are needed that assess whether polygynous male resource allocation decisions about life history traits are density dependent. We tested for an influence of density on age-specific life history traits in male southern elephant seals, Mirounga leonina, using a 34-year data set collected at Marion Island. Specifically, we determine whether life history varied with density-related factors for survival, improved breeding success (measured as social status) and recruitment age. This was done by selecting linear models that tested biological hypotheses about density-dependent covariates related to competition intensity during breeding and natal conditions, while accounting for known intrinsic effects such as age and social status. Baseline mortalities were higher for males that had accumulated above average reproductive costs for their age than males with below average costs. This reproductive cost was determined by the number of females per harem relative to the population average. Thus, males likely allocated more resources to reproduction and less to body maintenance at all ages when defending and servicing relatively large harems, and this cost was compounding for males that dominated large harems at a young age. Males born in years with few pups were more likely to be dominant breeders and recruit at an earlier age than males born in years with many pups. Thus, breeding success and recruitment age likely depended on the population density experienced during early life, suggesting lasting effects of natal conditions in a long-lived animal. We show how density-dependent factors interact with intrinsic determinants of resource allocation to determine variation in polygynous male life history with long-term consequences.

AbstractRoss seals (Ommatophoca rossii) travel away from the pack ice and spend most of their year foraging pelagically. Here, we augment the few existing records of Ross seal diving and haul-out behaviour, providing novel insights into how these are influenced diurnally and seasonally. We used biologging devices that recorded the dive behaviour (n = 5) and/or haul-out behaviour (n = 9) of Ross seals in the eastern Weddell Sea (2016–2019). Ross seals mostly dived between 100 and 200 m deep, often > 300 m, and for 5–12 min in duration, often > 20 min. During March–July, when Ross seals forage pelagically, diving metrics varied diurnally. The seals dived deeper during twilight and shallowest at night, while the number of dives and diving duration did not follow a clear diurnal pattern. Consequently, diving effort was highest during the night. Ross seals preferentially hauled out in the middle of the day during September, October, February and December, but not during the rest of the year. Three females that entered the pack ice during breeding season were hauled out continuously for 5–7 days, punctuated by water entries for 1–3 h during and/or after such continuous haul-outs over the breeding season. This behaviour might suggest that Ross seals alternate between capital and facultative income breeding.

Population-level shifts in reproductive phenology in response to environmental change are common, but whether individual-level responses are modified by demographic and genetic factors remains less well understood. We used mixed models to quantify how reproductive timing varied across 1772 female southern elephant seals ( Mirounga leonina ) breeding at Marion Island in the Southern Ocean (1989–2019), and to identify the factors that correlate with phenological shifts within and between individuals. We found strong support for covariation in the timing of breeding arrival dates and the timing of the preceding moult. Breeding arrival dates were more repeatable at the individual level, as compared with the population level, even after accounting for individual traits (wean date as a pup, age and breeding experience) associated with phenological variability. Mother–daughter similarities in breeding phenology were also evident, indicating that additive genetic effects may contribute to between-individual variation in breeding phenology. Over 30 years, elephant seal phenology did not change towards earlier or later dates, and we found no correlation between annual fluctuations in phenology and indices of environmental variation. Our results show how maternal genetic (or non-genetic) effects, individual traits and linkages between cyclical life-history events can drive within- and between-individual variation in reproductive phenology.

Megafauna, such as southern elephant seals (SESs) (Mirounga leonina, Linn.), forage in diverse, seemingly limitless habitats. In pelagic settings, their behaviour is more likely to be limited by physiological ability and prey distribution, than physical barriers. For elephant seals, their rapid growth in body size corresponds to changing physiological abilities. These changes are most pronounced for male elephant seals. While most studies have compared male and female SESs in terms of changing body size and physiological ability, few studies have compared the influence of changing body size on behaviour of male SESs from the same population using long term satellite tracking data. We describe age-related differences in movement and diving behaviour for male SESs from Marion Island. We analysed satellite tracking data collected from 23 male SESs seals fitted with Sea Mammal Research Unit Satellite Relay Data Loggers at Marion Island between 2005 and 2011. Each dive was assigned a behavioural mode, either 'searching' or 'transit', using state-space modelling. We used mixed-effects models to quantify the influence of age and behavioural mode on dive duration, surface duration, dive depth and number of daily dives. Younger seals travelled significantly further from Marion Island and spent most of their dives in transit mode, whereas older seals stayed closer to the island but were in searching mode for most of their tracks. When searching, older seals dived more frequently, displayed longer dive and surface durations, and reached greater depths than younger seals. These differences in diving behaviour seem to reflect changing physiological ability. For male SESs, changes in physiological ability necessitate behavioural plasticity, which may be the key to survival and future breeding success. Robust males are more likely to breed and must therefore, maintain their body size by adapting to local oceanic conditions.

The present study examined whether sweat glands are present in the skin of sub-Antarctic fur seals, Arctocephalus tropicalis, using standard histological procedures and light microscopy. Aspects of the microanatomy and histology of skin were described to elucidate structure and function. Sweat glands were present both in the furred areas of the body trunk, as well as in naked skin areas of the flippers. The density of the apocrine sweat glands appeared higher in fur-covered areas than in naked areas, while the size of sweat glands was similar amongst naked and fur-covered skin. The superficial position of sweat glands in the dermis of naked skin areas and the large, coiled, tubular nature of the secretory portion seem to indicate sweat gland activity in contrast to the deep lying, narrow sweat glands in fur-covered areas.

Carcasses resulting from natural mortalities are invaluable for use in scientific studies, provided species, sex, and age class are known. When such data are unavailable, identifying skeletal remains is necessary if one is to use the information contained within samples. Teeth are amongst the best preserved skeletal remains owing to the durability of enamel and dentine. Here, we tested whether external measurements of canines could be used to distinguish two partially sympatric species of Southern Ocean fur seals, the Antarctic Arctocephalus gazella and Sub-Antarctic A. tropicalis fur seals. We also investigated whether the external measurements of canines could be used to determine the age, sex, as well as island of origin of the animals. Eight morphological variables (crown length, root length, crown width, root width, crown thickness, root thickness, total canine length, and count of external surface annular ridges) were recorded from canines of 340 individuals of known species, sex, and island of origin. The count of external annular ridges provided a good estimate of age, which was confirmed by counting the growth layer groups of sectioned teeth, especially for older animals (> 9 years old). External canine measurements proved useful in distinguishing species, as well as sex within and between species, particularly in adult animals. Species were more difficult to distinguish in females than in males. The islands of origin could only be inferred in male Antarctic fur seals. This study indicates that fur seal teeth of unknown provenance, found either in breeding colonies or as vagrants, provide evidence on species, sex, and age of the animal, which increases the value of associated samples. It further highlights the importance of external measurements of skeletal remains such as canine teeth in separating closely related species.

Southern elephant seals Mirounga leonina have a circumpolar distribution and migrate across broad geographic regions. Therefore, they can provide important insights into the responses of top predators to changes in the environment, especially those effected by climate change. For this, determining trophic interactions is key, and thus it is important to investigate the diet of all populations of M. leonina in the Southern Ocean. Limited literature exists on the diet of southern elephant seals at the Prince Edward Islands in the sub-Antarctic. During August and September 1976, the stomach contents of two juvenile male southern elephant seals were opportunistically collected at Marion Island (46 o 54’S, 37 o 51’E), and later analysed. Accumulated cephalopod beaks ( n = 137) representing 18 taxa in nine decapod families were found. Onychoteuthidae was numerically the most abundant (28.7%), followed by Brachioteuthidae (21.8%), Neoteuthidae (12.6%), and Histioteuthidae (9.2%). Slosarczykovia circumantarctica (Brachioteuthidae) was the most abundant species (19.5%) followed by Batoteuthis skolops (Batoteuthidae) at 12.6%. Allometric equations using lower rostral lengths showed that the southern elephant seals ingested cephalopods with mantle length between 5.2 and 39.9 cm and weighing between 0.003 and 2.62 kg. There was only one very digested crustacean, and no recognizable fish remains in the stomach contents. The continuation of the investigation relies on examination of natural mortalities and dietary items obtained by stomach lavage of individuals, complemented by, for example, stable isotope compositions captured along the length of vibrissae and within dentinal growth layer groups of teeth as proxies for the elephant seals’ trophic ecology.

Aim Climate change will likely lead to a significant redistribution of biodiversity in marine ecosystems. We examine the potential redistribution of a community of marine predators by comparing current and future habitat distribution projections. We examine relative changes among species, indicative of potential future community-level changes and consider potential consequences of these changes for conservation and management. Location Southern Indian Ocean. Methods We used tracking data from 14 species (10 seabirds, 3 seals and 1 cetacean, totalling 538 tracks) to model the habitat selection of predators around the Prince Edward Islands. Using random forest classifiers, we modelled habitat selection as a response to a static environmental covariate and nine dynamic environmental covariates obtained from eight IPCC-class climate models. To project the potential distribution of the predators in 2071-2100, we used climate model outputs assuming two greenhouse gas emission scenarios: RCP 4.5 and RCP 8.5. Results Analogous climates are projected to predominantly shift to the southeast and southwest. Species' potential range shifts varied in direction and magnitude, but overall shifted slightly to the southwest. Despite the variable shifts among species, current species co-occurrence patterns and future projections were statistically similar. Our projections show that at least some important habitats will shift out of national waters and marine protected areas by 2100, but important habitat area will increase in the Convention on the Conservation of Antarctic Marine Living Resources Area. Predicted areas of common use among predators decreased north of the islands and increased to the south, suggesting that multiple predator species may use southerly habitats more intensively in the future. Consequently, Southern Ocean management authorities could implement conservation actions to partially offset these shifts. Main conclusions Overall, we predict that marine predator biodiversity in the southern Indian Ocean will be redistributed, with ecological, conservation and management implications.

Whilst southern elephant seals Mirounga leonina inhabit the Southern Ocean, hauling out on sub-Antarctic islands, individuals are frequently encountered further north, on southern hemisphere continents. It is unknown whether these animals are merely vagrants or whether they are individuals using the extremes of their range. A single adult male, identified by characteristic scars, was sighted 37 times from 2008 to 2021 at Possession Island, Namibia. The timing of sightings indicates that this individual must have remained in African waters between at least some of its haul-outs, rather than returning to the Southern Ocean. Similar observations have been reported anecdotally for other individual adult male elephant seals on the southern African coast, whilst adult females pupping in this area are extremely rare. Although records of vagrant southern elephant seals hauling out on the southern African coast remain rare, whether they are single or repeated visits, in some instances repeated haul-outs represent dispersion to rewarding foraging areas.

Management of gases during diving is not well understood across marine mammal species. Prior to diving, phocid (true) seals generally exhale, a behaviour thought to assist with the prevention of decompression sickness. Otariid seals (fur seals and sea lions) have a greater reliance on their lung oxygen stores, and inhale prior to diving. One otariid, the Antarctic fur seal (Arctocephalus gazella), then exhales during the final 50–85% of the return to the surface, which may prevent another gas management issue: shallow-water blackout. Here, we compare data collected from animal-attached tags (video cameras, hydrophones and conductivity sensors) deployed on a suite of otariid seal species to examine the ubiquity of ascent exhalations for this group. We find evidence for ascent exhalations across four fur seal species, but that such exhalations are absent for three sea lion species. Fur seals and sea lions are no longer genetically separated into distinct subfamilies, but are morphologically distinguished by the thick underfur layer of fur seals. Together with their smaller size and energetic dives, we suggest their air-filled fur might underlie the need to perform these exhalations, although whether to reduce buoyancy and ascent speed, for the avoidance of shallow-water blackout or to prevent other cardiovascular management issues in their diving remains unclear.This article is part of the theme issue ‘Measuring physiology in free-living animals (Part I)’.

Climate variability and changes in sea ice dynamics have caused several ice-obligate or krill-dependent populations of marine predators to decline, eliciting concern about their demographic persistence and the indirect ecological consequences that predator depletions may have on marine ecosystems. Pack-ice seals are dominant ice-obligate predators in the Antarctic marine ecosystem, but there is considerable uncertainty about their abundance and population trends. We modelled the density and distribution of pack-ice seals as a function of environmental covariates in the southern Weddell Sea, Antarctica. Our density surface modelling approach used data from aerial surveys of pack-ice seals collected in the 2013/14 austral summer. Crabeater seals Lobodon carcinophaga, the most numerous pack-ice seal we observed, occurred at the highest densities in areas with extensive sea ice near the continental shelf break, but were almost absent in areas of similar sea ice concentration in the southern extent of the Weddell Sea. The highest densities of Weddell seals Leptonychotes weddelli, which were less abundant than crabeater seals within the pack-ice habitat, were predicted to occur over the continental shelf, near the shelf break. The distribution of both seal species broadly corresponded with the distribution and relative abundance of their main prey (Antarctic krill Euphausia superba and Antarctic silverfish Pleuragramma antarctica) obtained from concurrent ecosystem surveys. Ross seals Ommatophoca rossii and leopard seals Hydrurga leptonyx were not detected at all and are apparently rare within the southern Weddell Sea. These results can contribute to biodiversity assessments in the context of marine protected area planning in this region of the Southern Ocean.

Phenological shifts are among the most obvious biological responses to environmental change, yet documented responses for Southern Ocean marine mammals are extremely rare. Marine mammals can respond to environmental changes through phenological flexibility of their life-history events such as breeding and moulting. Southern elephant seals (Mirounga leonina) undergo an obligatory annual moult which involves the rapid shedding of epidermal skin and hair while seals fast ashore. We quantified the timing (phenology) and duration (the time from arrival ashore to departure) of the moult haulout of 4612 female elephant seals at Marion Island over 32 years. Using linear mixed-effects models, we investigated age, breeding state and environmental drivers of moult timing and haulout duration. We found no clear evidence for a temporal shift in moult phenology or its duration. Annual variation in moult arrival date and haulout duration was small relative to age and breeding effects, which explained more than 90% of the variance in moult arrival date and 25% in moult haulout duration. All environmental covariates we tested explained minimal variation in the data. Female elephant seals moulted progressively later as juveniles, but adults age 4 and older had similar moult start dates that depended on the breeding state of the female. In contrast, moult haulout duration was not constant with age among adults, but instead became shorter with increasing age. Moulting is energetically expensive and differences in the moult haulout duration are possibly due to individual variation in body mass and associated metabolizable energy reserves, although other drivers (e.g. hormones) may also be present. Individual-based data on moult arrival dates and haulout duration can be used as auxiliary data in demographic modelling and may be useful proxies of other important biological parameters such as body condition and breeding history.