Mark Andrew Hindell

High Pathogenicity Avian Influenza (HPAI) H5N1 clade 2.3.4.4b has spread beyond birds to affect seals across the Southern Ocean and sub-Antarctic region, with southern elephant seals ( Mirounga leonina ) particularly devastated. The virus, likely introduced via spillover from infected migratory birds, has killed tens of thousands of adult seals and pups throughout most of their range, though Macquarie Island remains unaffected so far. We used twenty years of elephant seal movement data from the southern Indian and Pacific oceans to assess whether seal-to-seal transmission could spread HPAI H5N1 between breeding colonies, despite the vast distances separating them (Marion Island, Iles Crozet, Iles Kerguelen, and Macquarie Island). There was substantial overlap in seals’ at-sea distributions during their winter post-moult trips, when seals travel for weeks at average speeds of 3.5 km/h. Two transmission pathways were examined: (1) terrestrial “stepping stone” routes, where infected seals could pass the virus between colonies during short intervals to remain infectious were feasible from Marion Island to Kerguelen but not from Kerguelen to Macquarie Island; and (2) at-sea encounters between seals, which occurred frequently enough to enable transmission. The findings suggest that once established at Macquarie Island, the virus could potentially spread further to New Zealand’s sub-Antarctic islands and mainland New Zealand. While seal-to-seal transmission appears possible, we conclude this is unlikely. Nonetheless, understanding at-sea contact rates enhances knowledge of H5N1 epidemiology and demonstrates the value of combining long-term population monitoring with movement data to understand wildlife disease dynamics.

Extreme episodic changes in Antarctic continental shelf regions, such as glacier calving or iceberg grounding, can fundamentally reshape regional sea-ice conditions. Weddell seals are obligate sea-ice predators and so may reflect ecosystem change around the Antarctic shoreline. From 2006 to 2024, the movements and diving behaviour of 35 female Weddell seals were studied using biotelemetry. Following the calving of the Mertz Glacier Tongue in February 2010, five females expanded into the previously unused Commonwealth Bay, where they undertook between 0.05 and 65.3% of their dives. This shift coincided with the establishment of persistent land-fast ice in the region (2019–2024), absent prior to calving (2006–2009). Residency times were positively associated with land-fast ice persistence. Although generalized additive mixed models detected no significant overall effect of calving on dive depth, dive duration, hunting time or hunting depth when averaged across the study area, all behavioural variables displayed pronounced spatial heterogeneity. This suggests that calving primarily altered the spatial distribution of diving and foraging behaviour rather than inducing uniform behavioural shifts. By contrast, this glacier calving event caused catastrophic breeding failures in seabirds, whereas even the resulting drastic sea-ice changes remained within the behavioural and spatial flexibility of Weddell seals.

Identifying the determinants of juvenile survival is crucial for understanding the population ecology of long-lived species, where parental guidance can influence naive juvenile survival rates. In southern elephant seals (Mirounga leonina), offspring receive no foraging site knowledge from their parents, only fat reserves. We focus on how movement patterns during the pups' maiden foraging trip influence their survival at Macquarie Island. We tracked weaned pups with satellite tags during their post-weaning migration and compared their movements to the post-moult winter migrations of adult females. We found that pups travelled predominantly in an easterly to south-easterly direction, in line with the Antarctic Circumpolar Current. The Antarctic Circumpolar Current may provide a passive survival advantage for naive pups, with current-following predicting survival probability. We propose an "accessibility area" concept in which currents expand the foraging area accessible to energy-limited pups, providing a theoretical framework that may apply broadly to marine species with naive dispersing juveniles. Adult females showed different dispersal patterns, travelling southwards towards Antarctic waters, suggesting that learned experience may influence their direction.

Animal‐borne conductivity-temperature-depth (CTD) and fluorescence sensors deployed on Southern Ocean elephant seals ( Mirounga leonina ) provide essential hydrographic and biogeochemical observations in remote Southern Ocean regions where shipboard and autonomous sampling is sparse. For these data to be fully integrated into the Global Ocean Observing System, their accuracy and consistency with established autonomous observing standards must be assessed. Here we present a dedicated field intercomparison of 20 CTD Satellite Relay Data Loggers (SRDLs), including nine equipped with Valeport Hyperion fluorometers, conducted against a shipboard SeaBird SBE 911plus CTD and an ECO FLBB fluorometer during a 2025 East Antarctic research voyage. Hyperion fluorometers systematically underestimated the ECO fluorometer by a consistent factor across deployments. We therefore recommend applying a single gain correction of 1.7±0.6 to Hyperion fluorescence measurements to align seal‑borne fluorescence with ECO fluorometers commonly used on biogeochemical Argo (BGC‑Argo) floats and other autonomous platforms. After application of this gain correction, established BGC-Argo delayed-mode physiological correction schemes can be applied to obtain more accurate chlorophyll estimates and improve cross-platform comparability. CTD temperature and salinity showed linear pressure‑dependencies comparable to previous SRDL sensor assessments, with mean (±1 standard deviation, s.d.) biases of 0.006±0.026˚C km ^-1 for temperature and 0.006±0.028 psu km ^-1 for salinity. If uncorrected, these pressure dependencies introduce additional uncertainty into delayed-mode adjustments (±0.04˚C and ±0.05 psu at 1000 m). Together, these results highlight the value of routine at‑sea calibration for improving CTD and fluorescence sensor accuracy and enhancing interoperability between seal‑borne, ship-based and autonomous oceanographic observations across the Southern Ocean.

Regional differences in southern elephant seal (Mirounga leonina) population trends have long been hypothesised to reflect environmental variation affecting prey availability. By integrating census counts, demographic data, and locally relevant winter sea-ice conditions, we provide new evidence quantifying the suspected link between seal numbers and regional sea-ice cover in the Southern Ocean. We developed an integrated population model using annual abundance and capture–mark–recapture data from 1980–2023, accounting for observation error and temporal random effects. Population breeding probability varied annually (50-65% on average). To assess how environmental conditions influence reproductive dynamics, we tested the effect of winter sea-ice cover within the known foraging range of adult females. We compared two covariate structures and a null model, incorporating one-year-lagged (B-COV1) and same-year (C-COV0) sea-ice conditions. Covariate models confirmed a negative relationship (βB-COV1 = -0.0103 to βC-COV0 = -0.0345), indicating that reduced population breeding probability was associated with higher-than-average sea-ice cover. Estimates of the total population size (N) mirrored the observed decrease in seal numbers. N was used to project historical scenarios representing persistently ’best’, ’neutral’, and ’worst’ case sea-ice cover conditions over the full timeseries. The scenario-specific intrinsic growth rates ranged from a slow decrease under the best-case scenario (r = –0.495%) to a substantially stronger decline under the worst-case scenario (r = –3.126%), with the neutral scenario closely matching the observed population trend (r ≈ –2%). These comparisons emphasise how local-regional scale habitat conditions can alter long-term population trajectories at magnitudes relevant to species recovery

Extreme episodic changes in Antarctic continental shelf icescapes—such as glacier calving or iceberg grounding—can reshape regional sea and icescapes. Grounded icebergs may block or enable sea ice advection, altering sea ice phenology and affecting nutrient and light cycles. These changes can shift phytoplankton bloom timing with repercussions throughout the food web. Ice-dependent species may lose or gain foraging habitats, affecting their reproductive rates and breeding success. Weddell seals, as resident polar predators, can act as sentinel species for detecting ecosystem changes caused by such events. Changes in seal movement ecology likely reflect changes in prey structure and distribution. From 2006 to 2024, the movements and diving behaviour of 34 female Weddell seals were studied using biotelemetry. Following the calving of the Mertz Glacier Tongue in February 2010, seals spent more time in Commonwealth Bay (from 0.9% to 13% of their post-calving dive locations), consistent with earlier formation of landfast ice (February 2019–2024) and its persistence post-calving. Landfast ice persisted in Commonwealth Bay from May onwards, although it was absent before the calving event (2006-2009). In Commonwealth Bay and west of Pointe Géologie Archipelago, seals also dived deeper after calving than before, suggesting changes in foraging strategies.

Population monitoring provides information on species conservation status. We reassess the status of the southern elephant seal population at Macquarie Island. The number of cows on the isthmus, ~20% of the total population, correlated with counts for the whole island (i.e. they reliably indicate island-wide trends). Cow numbers within the isthmus decreased from ~9400 in 1949 to ~2550 in 2023 at −1.1% year⁻¹, similar to the −0.8% year⁻¹ from 1984 to 2023 when counts were made annually (before 1984, counts were less systematic). This contrasts with all other southern elephant seal populations, which are either stable or increasing. There was also considerable year to year variability (± 350 cows year⁻¹) in the numbers of cows ashore, indicating individuals skipping breeding. Counting errors may contribute to this variability but are unlikely given that the isthmus study area harems are small, typically < 200 cows. We found no link between cow numbers and summer ocean conditions using the Southern Annular Mode as a proxy (i.e. prior to blastocyst implantation), and it remains unclear what is causing this variation. Nonetheless, several other studies have suggested changing prey conditions during the winter are the most likely cause of this overall and ongoing decrease.

Over the last 20 years (2004 to 2025), a French-Australian research and ocean observing collaboration has collected >400,000 temperature-salinity profiles providing broad coverage within the Indian Sector of the Southern Ocean. The collaboration is the cornerstone of the emerging global Animal-Borne Oceanographic Sensors (AniBOS) network, from which the data are freely available to the operational, ocean and climate research, and public communities. These data are a primary source of information for the study of ocean properties in this remote region, enabling major advances in knowledge of dense water formation, glacial ice shelf melting, frontal structure and recent trends driven by climate change in the Southern Ocean. The data have also provided key observations of biological processes, redefining our understanding of the ecology of seals in the Southern Ocean and providing a detailed picture of how they utilise their dynamic ocean-ice environment. The two-fold delivery of essential oceanographic and ecological observations makes this a flagship program, one which has enabled a step-change in our understanding of coupling between physics and biology. Sustaining the observations delivered by AniBOS is critical within the context of a rapidly changing Southern Ocean, for detecting change and anticipating consequences for these unique coupled systems.