Antarctic fur seals swimming 10,000km

Updated June 29, 2009 17:49:19

For years scientists thought Antarctic fur seals spent their winters gorging themselves on fish. But it turns out the fur seals winter is anything but relaxing. The seals are swimming up to 10,000 kilometres as they make multiple trips between sub-Antarctic islands and the rich fishing grounds at the polar front.


Presenter:Felicity Ogilvie
Speaker: Doctor Mary-Anne Lea, from the Antarctic Wildlife Research Unit at the University of Tasmania; Chris Oosthuizen, South African scientist

FELICITY OGILVIE: It started as a study on the winter feeding habits of Antarctic fur seals.

Doctor Mary-Anne Lea from the Antarctic Wildlife Research Unit at the University of Tasmania has put tracking tags on 80 seals.

The seals were tagged in their summer breeding ground on Marion Island - a sub-Antarctic island that's between South Africa and Antarctica.

MARY-ANNE LEA: Here we've got the tracks of two Antarctic fur seals, which were tagged at Marion Island in 2008, and you can see as they move southwards during the winter slowly travel up to 1300 kilometres from the island down to the polar frontal area.

FELICITY OGILVIE: When the seals hit the polar front they gorge themselves on fish and krill; that's what Doctor Lea expected. What the seals did next was a surprise.

MARY-ANNE LEA: One of the very interesting findings for us is that these animals are essentially commuting to the polar front each winter, sometimes making three to four trips over the eight months of the winter, and in each instance doing a round trip of over 2,500 kilometres.

FELICITY OGILVIE: The seals are travelling up to 10,000 kilometres each winter. What makes the journey more extraordinary is the fact the team only tagged female fur seals, and most of those seals are pregnant.

MARY-ANNE LEA: For us it kind of… it changes the focus of the study a little in that it makes some of the ecological questions more interesting in terms of why animals would bother, essentially, to go to the same area.

So, it raises questions about predation pressure at the polar front potentially, perhaps from killer whales or other species; whether resting is important for the females while they're gestating, getting ready to raise their pup. It's good for them to rest on land?

FELICITY OGILVIE: South African scientist Chris Oosthuizen has been tagging the seals that breed on Marion Island.

CHRIS OOSTHUIZEN: It's wet and windy and very wet. You get about 2,500 millimetres of rain; it's a sub-Antarctic climate and the vegetation is also sub-Antarctic.

There's no plants that's higher than your knee; mostly grasses and mires, which is, sort of, water-locked swell sponge grounds, and things like that.

FELICITY OGILVIE: And whereabouts are the seals? Hauled out on beaches?

CHRIS OOSTHUIZEN: Yeah, most of them, most of the fur seals like to haul out on rock… rocky beaches. They gazelles in particular haul out on these rock beaches, which has access to vegetation type… or vegetation behind the beaches, where they actually go.

As the pups grow older they move from the beach to those vegetation areas behind the beaches.

FELICITY OGILVIE: Doctor Lea says because the seals breed on the beaches in summer but haul themselves up into the tussock grasses in winter it's been easy for them to go unnoticed.

MARY-ANNE LEA: Particularly as we've spoken to collaborators… and generally the feeling is that the odd fur seal shows up here and there at these sites during the winter.

But I guess because they're not breeding there and they're able to haul out wherever they like and rest in the tussocks, and no-one's really suspecting them to be there, nobody really had much of an idea that these animals were coming and going as regularly as they are.

FELICITY OGILVIE: The scientists will now try to work out why the seals are making such a marathon journey every winter.