Clive R. McMahon

All air-breathing marine vertebrates face the same fundamental trade-off: time spent foraging underwater must be offset by surface recovery between dives. For decades, the dominant view in diving physiology has been that post-dive duration (PDD) reflects the repayment of oxygen debt and clearance of carbon dioxide and lactate. Using more than 800 000 dives from five sea lion species across 18 colonies spanning tropical to subpolar waters, we quantified how PDD scales with dive depth and duration and evaluated whether this pattern is consistent with metabolic recovery interpretations or instead points to depth-linked constraints. We found that PDD increases primarily and linearly with depth, while dive duration contributes to PDD only at greater depths, a relationship conserved across species despite pronounced differences in body mass, dive physiology and foraging ecology. Our findings conflict with predictions of metabolic recovery interpretations and point to a pressure-linked mechanism in which time at depth and resulting inert-gas loading shape surface recovery. By highlighting pressure-linked inert-gas management as a central candidate mechanism for surface interval regulation in inhalation divers, our study revises a central assumption in diving physiology, with broad consequences for understanding foraging efficiency, habitat accessibility and vulnerability to environmental change in air-breathing marine vertebrates.

The world’s ocean stores ~90% of the excess heat generated by anthropogenic global warming, making sustained ocean observations essential for understanding physical, biological and climate processes. Here, we describe how the Integrated Marine Observing System (IMOS) Animal Tagging Facility, in collaboration with national and international partners, has established a unique animal-borne ocean-observing system. Wide-ranging, deep-diving marine predators provide critical observations from remote and under-sampled regions, particularly the Australian Antarctic sector and tropical northern Australia, complementing traditional observing networks. Since 2004, IMOS Animal Tagging has deployed 1023 instrumented tags on southern elephant (n = 746) and Weddell seals (n = 125), Australian sea lions (n = 50), Australian (n = 8) and New Zealand fur seals (n = 24), and olive ridley (n = 24), green (n = 10) and flatback turtles (n = 16). These deployments have yielded more than 420,000 temperature–salinity–depth profiles spanning the Antarctic to the tropics. The resulting observations have advanced understanding of ocean structure, bathymetry, climate processes and the ecology of wide-ranging marine vertebrates, while providing valuable data to operational oceanography and climate research. Twenty years of sustained observations have demonstrated the importance of long-term, continuous animal-borne data streams as a core component of Australia’s IMOS.

The sea ice zone plays important ecological roles in Antarctica, influencing phytoplankton bloom timing, which cascades through the food web, and providing habitat for many species. Weddell seals...

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.

Highly pathogenic avian influenza of subtype H5N1 (HPAIV H5N1) reached Antarctica in late 2023/2024 breeding season, but the host ecology and movement processes shaping its incursion and spread remain poorly resolved. We investigated these mechanisms by integrating viral genomics, multi-season serology, and seabird movement data at King George Island (Fildes Peninsula, South Shetland Islands), a likely gateway between South America and the Antarctic Peninsula. Across three breeding seasons (2022/23–2024/25), we collected swabs and blood serum from key scavenging and predatory seabirds (Brown skua, South Polar skua, Southern Giant petrel) and paired these data with light-level geolocator tracks (10–16 full annual tracks per species) and breeding-season GPS tracks (10–20 individuals per species). Phylogenetic analyses including three newly generated HPAIV H5N1 genomes from infected Brown skuas placed these viruses within the South Georgia–Antarctic lineage, consistent with introduction via South Georgia followed by onward spread within the region. Longitudinal serology revealed a rapid increase in cumulative exposure in scavenging species, with antibodies against influenza A virus’ nucleoprotein and hemagglutinin subtype H5 rising to high levels by 2024/25 in Brown skuas (52.2%) and Southern Giant petrels (62.5%), but remaining markedly lower in South Polar skuas (12.5%), consistent with their more pelagic and less scavenging foraging behaviour. Tracking showed that migratory connectivity was greatest during the non-breeding period but contracted rapidly during colony return and early breeding. In contrast, network simulations parameterized by high-percentile breeding-season foraging distances indicated strong peninsula-wide connectivity and non-zero potential links toward South Georgia and other sub-Antarctic stepping-stones. Together, these results provide a mechanistic, host-based framework suggesting that HPAIV H5N1 likely reached Antarctica through the South Georgia pathway, but that its regional spread was shaped primarily by foraging ecology and breeding-season movement networks rather than by long-distance migration.

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.

Tropical cyclones draw their energy from warm seas and, all other things being equal, the warmer the ocean surface, the more intense the storm. However, tropical cyclones also cool the surface ocean primarily by mixing it with deeper, cooler waters. The ‘cold wake’ acts as a negative feedback–reducing the storm’s intensity. Our ability to incorporate this information in forecasts is limited by a lack of ocean observations within tropical cyclones, particularly in shallow seas inaccessible to autonomous Argo floats. Here, we show observations of the response of the upper ocean to five tropical storms obtained from sea turtles instrumented with oceanographic sensors. The turtle observations captured key ocean processes, such as mixing induced ocean cooling, that are important for forecasting. In comparison, an ocean reanalysis system that blends existing ocean observations but notably, not the turtle observations, with an numerical ocean model, fails to capture many of the processes responsible for the surface ocean cooling. Having shown the utility of the observations for ocean-tropical cyclone interaction studies, we discuss the role that a turtle based observing system could play in monitoring and forecasting tropical cyclones worldwide.