The elephant seals have started arriving in the Vestfold Hills for their annual moult. Southern elephant seals breed and moult on a number of sub-Antarctic islands. However, there are instances where seals have bred in the high Antarctic, for example on Petersen Island, or in temperate regions like on King Island in Bass Strait and even in Western Australia.
After the breeding season, moulting commences when seals return to land. Moulting generally occurs on the breeding islands in the sub-Antarctic, but also in the Antarctic e.g. the Vestfold Hills. The elephant seal moult is dramatic and the seals shed both their hair and the first layer of skin. This process takes between 30 days for younger seals and up to around 55 days for older sub–adult males. It is at the end of the moult that we attach our state–of–the–art oceanographic trackers to the seals.
These trackers don’t only provide information on seal movement but collect information of ocean conductivity i.e. ocean salinity, ocean temperature and depth. Conductivity, temperature and depth or CTD information are the essential observations needed to quantify ocean structure and hence state of the ocean.
Because the seals can dive to great depths — up to 2100 metres, they are collecting data on water column structure that is important for understanding how Antarctic bottom water is formed. Understanding how and where this bottom water is formed is important for interpreting global heat and oxygen mixing rates.
Despite the importance of the Southern Ocean little is known about its physical structure, especially South of 60° where conventional sampling using ships and ARGO floats is, at best, sparse. Attaching high resolution oceanographic sensors to animals is resolving the paucity of data from South of 60°. Importantly, animal tracking data can provide valuable insights by collecting data over a number of years from predictable migratory routes across vast swathes of the Southern Ocean.
Individual animal-borne CTDs allow us to record physical properties of the ocean and to quantify those attributes in areas of ecological importance to animals. The Integrated Marine Observing System (IMOS) is supporting tracking of several species in the Southern Ocean using CTD tags and has so far provided more than 90 000 CTD profiles in the Southern Indian Ocean. The Davis team of seal researchers (Clive, Esther and Fernando) are building on this incredible time series of 13 years of observations and have so far this summer deployed five of the CTD tags on male elephant seals at Davis station which complements deployments at Iles Kerguelen in a sister project also supported in part by IMOS.
Our work tracking seals, where we integrate in situ physical attributes of the environment with animal performance are helping us get a much better handle on how the environment influences individual animal performance, population structure and persistence and ultimately ecosystems’ structure.
As with any study, success depends on a lot of people and organisations and we would like to thank: the Australian Antarctic Division for supporting our work here at Davis, IMOS for supporting long–term and incredible time series of unique ocean observations, all of the wonderful folks at Davis station that have made us very welcome on base and been helpful at every opportunity and of course all of our families and friends back home for supporting our Antarctic adventures.
Clive (Seal Researcher)