Predator and "oceanographer", Elephants Seals in the Southern Ocean

To investigate the foraging behaviour of elephant seal in relation to oceanographic features and for a better understanding of the differences in the demographic  trajectories of the main southern elephant seal population an international research project, associating, Australian, British and French scientist  was initiated in 2004. Elephant seals were fitted with a new generation of argos transmitters incorporating, pressure, temperature, salinity sensors, developed by the Sea Mammal Research Unit. The elephant seal become valuable auxiliaries for operational oceanography, and enables scientists to study the hydrology of the southern ocean, still largely unknown.

The migratory patterns of southern elephant seal respond to oceanographic conditions

At sea, elephant seals dive deeply and continuously, to travel, rest and forage. 60 to 80 20 to 30-minute dives are performed daily and elephant seal spend about 90 % of their time underwater at depth ranging between 400 to800 meters, with dives reaching up to 1800 m. One of the study objective was to quantify the influence of oceanographic conditions on the spatial distribution and the foraging success of elephant seal. The most favourable foraging areas can be characterized by the combination of several approaches : change in travelling speed, diving behaviour or body density affecting the diving behaviour.

The unknown southern ocean

The southern ocean is probably the least accessible and charted ocean on the planet. However this ocean plays a key role in heat exchange between the atmosphere and very few oceanographic data are available for this sector. 10 elephant seals from Kerguelen were equipped in 2004 and 3090 CTD and 803 TD high resolution casts (Fig 1) were obtained (total : 3893; Max depth 1500 m, mean 590 ± 205 m,. The data were validated, corrected and sent to the Coriolis data base.

The number of casts obtained by the elephant seals and their spatial distribution are indicated in color in fig. 2. South to 60° S, the number of CTD casts collected by seals over a 7-month period was 2260 against 182 originally archived in the Coriolis data base. Thus the use  of marine predators to acquire oceanographic data to try and understand the consequence of global warning has proven to be a very promising method for studying large scale climate and ocean phenomena.

Interpolated temperature casts from the data collected by the 9 elephant seals equipped at Kerguelen by the new  Argos CTD tags, during their first month at sea (March 2004).	Contribution of the elephant seal in 2004 to the Coriolis  temperature and salinity data set for the Southern Ocean  sector visited by elephant seals

This program was conducted with the financial and logistical support of Cnes (Tosca), l'Institut Polaire and the groupe Mission Mercator/Coriolis and is part of a national and international (Sea Mammal Research Unit, GB : M. Biuw, M. Fedak and Antarctic Wildlife Research Unit, Australie : M. Hindell) collaborative network.