What leopard seals can tell us about the health of the planet

11 July 2006

Dr Tracey Rogers in the Antarctic.
Dr Tracey Rogers in the Antarctic.

Around the ice floes of Antarctica, the leopard seal is king: top of the food chain, an efficient killer with no natural predators, untroubled even by man.

But despite its natural advantages, the leopard seal faces an uncertain future. Supplies of one of the Southern Ocean's main food sources, krill, are in decline, with losses of up to 80 per cent in some areas in the past 30 years. Meanwhile a 6C rise in temperatures in the last half century has caused the disappearance of large areas of sea ice on which the seals breed.

The effect of these changes on the leopard seal population is being closely monitored by Dr Tracey Rogers, an adjunct senior lecturer in the Faculty of Veterinary Sciences and the director of the Australian Marine Mammal Research Centre. Her findings will have a bearing not only on the ecosystem of Antarctica, but on the world at large.

"The Antarctic drives the climate of the planet," said Dr Rogers, delivering the annual J.D. Stewart Address for the Veterinary Science Foundation. "For us in Australia it is really important - it determines whether we have droughts, fires and floods."

Dr Rogers has been researching seals in Antarctica for 15 years, spending part of each year on the ice floes. An ecologist with a PhD from the Faculty of Veterinary Science, she won an Australian Young Tall Poppy Award in 2005.

With 2007 designated as the International Polar Year by the World Meteorological Association, Dr Rogers's research will use the leopard seal as a model to show the influence of climate change on the Antarctic pack ice zone.

"Climate change is already a reality," she said. Ice-core data shows a dramatic increase in the amount of carbon dioxide in the atmosphere over the past 1000 years, particularly since the start of the Industrial Revolution. The oceans are warming, weather patterns getting more extreme, while in the Antarctic glaciers are retreating and ice shelves calving - one shelf that detached itself stretched as far as from Sydney to Canberra.

Scientists now estimate that between 18 and 35 per cent of species in some areas of the world will be on the road to extinction by the middle of the century. In the Antarctic, said Dr Rogers, leopard seals would be among the first to respond to large-scale environmental change, and were key to understanding ecosystem changes.

Dr Rogers revealed how she uses acoustic technology to track seals under the ice, monitoring their underwater calls during the breeding season. The male seals sing continually for two months of the year, and their calls can be tracked over a distance of 31 square kilometres.

Useful information about the seals' foraging patterns can also be extracted from scientific analysis of different tissues. "We can also look back into the past and use the samples collected by Douglas Mawson, Ernest Shackleton and other explorers," she said.

"We can see how the leopard seals have adapted to changes in the past century, and that will allow us to predict how they will cope with changes in the future."

Answering questions, Dr Rogers said the long-term depletion of krill stocks was of enormous concern and would inevitably affect the Southern Ocean's whale population. She called for an end to the commercial harvesting of krill, which is used for fertiliser and human consumption, particularly in Japan.

Contact: Richard North

Phone: 02 9351 3720