Seals reveal secrets of polar oceans

3 June 2013 by Alison Smith

Seals wearing special tags are playing a vital role in collecting temperature and salinity measurements from the polar oceans, delivering insights for weather forecasters, climate scientists and biologists, according to a new review.

Elephant sealPolar seas play a critical role in climate and weather systems, but they are poorly understood. Data collection is difficult and expensive, especially during the long, harsh winter, and sea ice prevents access by ships or floating buoys.

This is where seals can help - they are ideal for collecting data close to shore and in pack ice. Elephant seals, for example, spend 90 per cent of their lives at sea, travelling up to 4000km on months-long feeding trips. They dive about 60 times a day, reaching depths of up to 2000 metres - deeper than a military submarine.

Although the idea of using animals to collect data had been around for some time, it was a biologist, Professor Mike Fedak, and his colleagues at NERC's Sea Mammal Research Unit who persuaded the scientific community to take it seriously. "We wanted to know more about the places the animals were visiting," he explains. "We'd ask the oceanographers 'what's the ocean like here?' but they didn't know. NERC was using Autosub (a robot submarine) to explore under the ice, and we thought 'we've got our own Autosub - the elephant seal!'"

The Sea Mammal Research Unit developed sophisticated tags that can measure temperature, salinity and pressure. They record a series of measurements at different depths while the seals are coming up from a dive, and transmit the stored profile up to a satellite when the animals surface to breathe. The tags are attached using fast-setting glue, and fall off naturally when the animals moult, up to 11 months later.

The first large-scale use of the tags was in 2003, when they were glued to the heads of 80 elephant seals at four colonies in the Southern Ocean. "Apart from being the coolest animal on earth, elephant seals are very approachable," explains Fedak. "It's easy to fix the sensors on and it doesn't seem to bother them. They spend a lot of time at sea, so the tags don't get scraped off on ice or rocks, and they go to some interesting places where it's hard to get data any other way."

Now the tags are being used by many countries including Norway, France, the US and Australia, and scientists are recruiting other species including Weddell seals, hooded seals and ring seals. "We choose animals and programme the tags to tailor them to where the oceanographers want to get data and to suit the behaviour of a particular species," says Fedak. "The beauty of it is that it's a partnership between oceanographers and biologists. It took a while for the oceanographers to accept it, but now they've really embraced it. It's so cost-effective compared to using ships."

Marine animals - including seals, turtles and diving birds - have now provided over 1·4 million temperature profiles. Over 300,000 of these also measured salinity - crucial for a full understanding of ocean processes. Animals have provided 70 per cent of all the profiles in the World Ocean Database south of 60°S.

The profiles are made freely available every day via the World Meteorological Office, for immediate use by weather forecasters and ship operators. After further processing they are stored in the open-access World Ocean Database. Scientists around the world are now using the data in models to study the role that oceans play in climate change, including how ice sheets form and melt.

The data can also reveal important insights into the behaviour of the animals themselves, including migration routes, feeding grounds and the distribution of different colonies. This can help with conservation policy, so animals benefit too.

Now seals are being recruited to the iSTAR project, to help find out why the ice sheets around the huge Pine Island glacier in Antarctica are breaking up, and what this means for sea levels. "It's a really exciting project," says Fedak. "There's a whole bunch of geologists, oceanographers and biologists camped out on the glacier, and seals are playing a really important part - helping to get data from under the ice, and during the winter."

The tags are being constantly improved. "In a couple of months, all our tags will have fluorescence sensors to measure chlorophyll concentrations, showing where plankton are abundant," adds Fedak. "Next we're working on sensors for oxygen, and then carbon dioxide. The possibilities are really expanding."

'The impact of animal platforms on polar observation' - MA Fedak. Deep-Sea Research Part II: Topical Studies in Oceanography, volumes 88-89 (Apr-May 2013), pages 7-13.