Elephant seals diving for science

Scientists like to talk about "vessels of opportunity". These are basically 'cheap' ways to hitch a ride for a scientific project, i.e. you jump on some pre-existing cruise and use their ship and trajectory to perform some of your own data collections. Since you have not been involved in planning, funding, organizing and managing of that cruise, you (the hitchhiker) are normally bound to tag along and take things as they come, go where they go, and try to make some sense out of it for yourself afterwards.

This has greatly increased many projects and their range and coverage, but there is still one limiting factor: there are only so many rides (i.e. scientific vessels) available. But with the advent of smaller and smaller scientific devices and satellite transmission systems, there is an entirely new fleet of "vessels of opportunity" at the scientists' disposal: seals!



Researchers of the Sea Mammal Research Unit (SMRU), Gatty Marine Laboratory, University of St Andrews have been quite successful with this approach in their SEaOS (Southern Elephant Seals as Oceanographic Samplers) project. It basically works like this: they attach a sensor/transmitter device (a 'tag') on a seal's head as shown above. Now, as the animals swim for thousands of km and dive down to 2,000m, their tags record details of temperature, depth and the salinity of the water, and when the seals pop up to breathe, the tags transmit their information to scientists in Scotland via satellite.



Of particular importance to the scientists are oceanic fronts, i.e. where warmer and colder waters meet and mix, much like atmospheric fronts we know from weather charts. Just like atmospheric front systems, the oceanic fronts are highly dynamic and can only be adequately understood and predicted if a sufficient amount and spatial coverage of observations is available.

The seals can help with this, since they occur in significant amounts on several of the subantarctic islands and as they have wide diving and swimming ranges, they frequently cover the oceanic front systems of Antarctica.



South Georgia's population at 400,000 is the biggest group and has been relatively stable since the end of large-scale hunting in the 1950s. But the groups centred on the islands of Macquarie and Kerguelen have not fared so well; and in the case of Macquarie may still be in decline. Why this is so may emerge from an analysis of the data gathered by the seals.

And in case you worried about the tags on the seal's heads: they fall off after about a year, when the animals moult (i.e. change fur).