IMOS has funded deployment of these tags for this program for ten years now, providing a continuous record of hydrographic profiles along the Davis-Kerguelen transect in the Southern Ocean. The tags Clive and his team will be attaching to the seals are sophisticated miniaturised conductivity-temperature depth tags that measure salinity, temperature and depth and four second intervals.
Prior to the IMOS program, seal tag deployments were carried out through the Marine Mammals Exploring the Oceans Pole to Pole (MEOP) program. MEOP data go back to 2004, so together with the ten years of IMOS deployments we have a long time-series, enabling greater understanding of the system and increased confidence in the accuracy of models being developed from the data.
“With this extraordinary time series that is growing each year we are now in a position where we can look for trends and patterns in oceanographic phenomena as well as increase our understanding of individual animals’ behaviour,” says Dr McMahon.
“As the time series grows so does our ability to make novel discoveries and with that the opportunities to answer bigger climate change questions such as finding new areas of the important Antarctic Bottom Water formation and locating areas of glacier melt,” he says.
Southern Elephant Seals dive 80–100 times per day in order to forage for food and they can dive to depths of 2,100 metres. They can remain submerged for up to two hours, so with frequent dives to great depths seals have the capacity to collect a lot of information about the ocean conditions they encounter.
When the seals surface, the monitors transmit signals to satellites, sending the information that has just been recorded in the ocean below. Data on salinity and temperature at particular depths can tell us much about sub-surface currents and other phenomena. This information can be gathered by other means but seals give us access to much greater areas, even under ice.
One of the things researchers will be looking at this year is the ‘foraging success’ of individual seals. This is about their success at finding food (generally squid and fish), which in turn affects reproduction success. PhD student, Fernando Arce, from the Institute for Marine and Antarctic Studies, is using the collected data to look at the angle of the dive in seals’ ‘drift dives’. This angle is related to the buoyancy of the animal which is determined by percentage of body fat. Mr Arce is looking at developing algorithms to help infer foraging success from the angle of the dive.
The longer we keep observing seals and their ocean habitat, the more we learn about variation in the system and this gives scientists greater predictive power.
Dr McMahon believes that in integrating data on physical oceanography with biological information on the foraging behaviour of seals, we can begin to understand the relationships between ocean conditions, how they are changing over time and their effects on seal behaviour and ‘performance’ (their overall health, survival and reproductive success).
“We’re interested in whether seals return to the same places for foraging and what physical factors may influence where seals go,” says Dr McMahon.
“Over time we may begin to see relationships between seal movements, their performance and their changing environmental conditions,” he says.
Logistical support for this project is provided through the Australian Antarctic Program and it has received funding from the Australian Antarctic Science Program.
IMOS seal data are freely available via the Australian Ocean Data Network Portal.
Related research paper using IMOS data:
McMahon, C. R., Harcourt, R. G., Burton, H. R., Daniel, O. and Hindell, M. A. (2017), Seal mothers expend more on offspring under favourable conditions and less when resources are limited. J Anim Ecol. doi:10.1111/1365-2656.12611