Revealed: the secret life of elephant seals
The secret life of elephant seals living around the Antarctic has been revealed thanks to new research from an international team of scientists. The results, published in the journal the Proceedings of the National Academy of Sciences, help to explain why some seal populations have remained stable while others have declined, and give clues as to how these animals will respond to climate change. The work involved attaching oceanographic sensors with satellite transmitters to 85 elephant seals at different locations around the Southern Ocean. The tags, which are the size of a pack of cards, were glued to the fur of the seals before they set off on their long foraging journeys. The tags were retrieved when the seals returned to the same beach to moult, up to 10 months later. While they were at sea the sensors picked up data on the animal's position, its depth while diving and the water temperature and salinity. In addition to this, the scientists were able to obtain information on the animal's condition by studying passive 'drift dives'. If the seals are getting enough food and gaining fat, they become more buoyant, whereas seals that are having difficulties finding food lose weight and so become less buoyant. Elephant seals spend most of the year at sea, and until now the only time the researchers could study them in detail was when they came ashore to breed. The new data have allowed the researchers to see where the seals go on their foraging trips and where they are most successful at finding food. 'These data are really exciting,' commented Mike Fedak of St Andrews University in the UK, who led the research. 'This new technology has allowed us to see where the seals go and understand their behaviour in the context of different characteristics of water in the Southern Ocean. The majority of animals from South Georgia fed within the Antarctic Circumpolar Current, but seals from other locations had a very different strategy, and visited colder waters near the continental shelf.' These different breeding strategies have implications for the animals' breeding success. 'The Indian and Pacific seals have to travel more than 1000 kilometres further during their winter migration than Atlantic seals,' explained Professor Mark Hindell of the University of Tasmania, one of the authors of the study. 'The extra energy expended would mean less breeding in years of low food abundance.' According to the scientists, this could offer an explanation as to why the seal populations in the Indian and Pacific sectors fell between the 1950s and 1970s, while populations in the Atlantic sector remained stable. That period saw a reduction in the amount of sea ice off east Antarctica; as the Indian and Pacific seals like to feed in the sea ice zone, the decline in sea ice may have contributed to the decline in those seal populations. Knowledge of the sea temperatures and salinities favoured by the seals is important for conservation efforts. Sea temperatures are predicted to rise by around 2°C over the next 100 years. Antarctic animals like the elephant seal face the dual challenge of coping with the increase in temperatures and competing with warm-water species which will move into the region as it warms up. The data collected by seals on their dives is also useful for oceanographers. 'The Southern Ocean is the hardest place in the world to obtain oceanographic data, especially during the wintertime,' commented Dr Mike Meredith of the British Antarctic Survey. 'The seals acted as 'samplers' to collect data from deep seas that we couldn't ordinarily access due to their remoteness and harsh environments.' The work was carried out as part of the international Southern Elephant Seals as Oceanographic Samplers (SEaOS) project, which is coordinated by the Sea Mammal Research Unit at St Andrews University and brings together British, French, Australian and American researchers.
Countries
Antarctica, Australia, France, United Kingdom, United States