Studying a little-known species of seal in Antarctica by Trevor McIntyre (Associate Professor, University of South Africa)
When I tell people that I study marine mammals, one of the first questions I am often asked (and a perfectly reasonable one at that!) is: “But you live in Pretoria…should you not be at the coast somewhere?”. In some ways yes, but then again, it doesn’t really matter if the animals one studies live mostly somewhere in the vast Southern Ocean and you have to travel to Antarctica in order to meet up with them….
As an academic, my interests lie in understanding behavioural adaptability that allows animals to survive in varied environments and how such adaptability may or may not help them to persist in environments that are rapidly changing due to human-related influences. I am working together with my colleague at the University of Pretoria, Dr Mia Wege, as well as a bunch of international collaborators on a project that aims to understand more about the behaviour and physiology of Ross seals (Ommatophoca rossii) in the Antarctic. Ross seals are one of four species of seals that breed on the ice surrounding the Antarctic continent – the other three being Weddell seals (Leptonychotes weddellii), crabeater seals (Lobodon carcinophaga) and leopard seals (Hydrurga leptonyx). While they’ve been recorded all around Antarctica, Ross seals are the least abundant of the four species and least studied as a result.
While some of the most seasoned international Antarctic researchers have never even seen a Ross seal, these animals haul out onto the sea-ice in reasonably predictable numbers in the area that is visited every year by the SA Agulhas II as part of the resupply operations to South Africa’s permanently inhabited research base, SANAE IV (see https://www.sanap.ac.za/).
This provides us with an ideal opportunity to not only get some insights into the biology of this species, but also collect quantitative data that will go a long way towards increasing our
understanding of how animals use the sea-ice zones and how ongoing ecosystem changes here are likely to affect their future success and survival.
We recently participated in the 2022/23 resupply voyage to SANAE to get the first field data collected for our current project on Ross seals. Our team on this expedition included four researchers – myself, Dr Wege, a masters student on the project (Candice Lewis) and field assistant (Andre van Tonder). While we also undertook surveys of seals along the track-line of the ship, the most important parts of our work involved catching seals, obtaining a few biological samples (small biopsy and blood sample, few whiskers and fur clippings) from them, and instrumenting with satellite-linked dive recorders (‘tags’). The capture process consisted of our team being lowered onto ice floes where seals were spotted via a crane fitted with a personnel carrier. Once on the ice floe, we used a net supported by an A-shaped frame to restrain seals while we collected samples and deployed tags. This in itself is not an easy task considering that seals can typically weigh close to 200 kg but is undertaken with care to ensure the safety of both the researchers and the seal. Once the seals were safely restrained in the net, we could proceed with all the various sampling procedures before releasing the seals again.
We use the biological samples to study various aspects of the physiology of seals, including their diet and capacity to dive for extending time periods. For example, as whiskers grow they retain tiny signatures of what the animal has been feeding on and where. This we can then decode by analysing the ratios of stable isotopes of elements such as nitrogen and carbon in the whisker, resulting in a time-series of data points that inform our understanding of what a seal has been foraging on and the likely latitudinal areas (i.e. how far south) where the seal was catching prey items. Potential prey items for this species include a variety of different small fish species (typically the small lanternfish belonging to the Family Myctophidae).
Deploying satellite tags on the seals that we captured formed one of the most important aspects of our field season. These small instruments record various parameters that give us some idea of the behaviour of seals. First and foremost, they provide us with location estimates for where the seals are after deployment for periods of up to one year. They also record time sequences of depth measurements (time-depth profiles) providing us with insight into the dive behaviours of individual seals. Additionally, some of the instruments are equipped with high-resolution temperature and conductivity sensors, recording characteristics of the water masses that Ross seals visit – such data being very valuable for oceanographers who otherwise find it difficult to obtain seawater data from the generally inaccessible and ice-covered regions that the seals inhabit.
Despite sea-ice levels in Antarctica reaching a new record minimum extent this past summer
(https://go.nasa.gov/3ZvPrX9), we were fortunate enough to encounter numerous Ross seals and to successfully complete our expedition. We successfully restrained and sampled a total of 28 seals during the voyage, but much of the real work only starts now. During the coming months, we’ll be monitoring their movements and behaviours and starting with the various laboratory analyses of the samples collected. Results will be made public as scientific articles when everything is done of course and we look forward to sharing some interesting and important findings
Dr McIntyre is a member of ARRA and he and his family live in our area.