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PRI's Environmental News Magazine

Antarctic Seals

Air Date: Week of July 27, 2001

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Reporter Allan Coukell recently joined a group of scientists on a trip to Antarctica. Their goal: to unravel the mysteries of the unusual mating behaviors of the Weddell Seal.

Transcript

CURWOOD: Some of the most isolated animals in the world are the Weddell seals in Antarctica. These mammals have an unusual mating system. They breed underneath the ice. By studying how these seals mate, scientists hope to get a better idea of the factors governing other animal mating systems. Alan Coukell recently joined a team studying these seals, and has this report.

[SOUND OF RADIO TRANSMISSION ON BOARD PLANE]

COUKELL: It is sunrise as I board the plane in Christchurch, New Zealand. I'm on a journey to a land 2,000 miles south where the summer sun never sets and the snow hardly melts.

[SOUND OF PLANE RADIO TRANSMISSION]

COUKELL: There are 60 of us. Mostly scientists and support staff, plus equipment, crowded into a U.S. Air Force Starlifter bound for the U.S. and New Zealand bases on Ross Island, Antarctica. Antarctica is one-and-a-half times the size of the United States. The driest, coldest, least populated continent on earth. To survive there, you have to adapt to the cold.

[SOUND OF PLANE RADIO TRANSMISSION]

COUKELL: We land on an ice runway, the surface of a frozen sea. As we emerge from the aircraft and into below-zero temperatures, every piece of skin that isn't covered begins to freeze. Not too far away on the ice, fat seals are lounging.

WAAS: Right now we're just looking for the females of the group that we studied last year.

COUKELL: This is the fourth Antarctic summer that Joe Waas and his colleagues have spent camped here on the sea ice near the seals. Waas is an animal behaviorist from the University of Waikato in New Zealand. He moves easily among the seals, gently lifting their rear flippers with the tip of his ice axe to expose their plastic identification tags.

WAAS: So this one here is yellow 965. [Sound of seal] Yeah. So it makes it nice and easy to sort of know who you're dealing with. [Sound of seal]

COUKELL: There are more than a hundred seals here, lying near an open crack in the ice. They're Weddell seals, gray with white spots. Most are female. Their pups, close by, have eyes as black as buttons. Joe Waas motions me to look a short distance away.

WAAS: There's a male that you should really see over here too. He's really beaten up. He got this, quite commonly the males that are running the show underneath the ice here will actually prevent other males from coming anywhere into these areas, and will chase them right out of these cracks in the ice.

COUKELL: This lone bull seal is a big fellow. He weighs at least 1,000 pounds. But he hasn't had an easy time of it. His flippers are torn, and there are gashes on both sides of his head. These seals are so placid, so unperturbed by our presence, that it's hard to imagine that right beneath our feet they're fighting a ferocious battle for dominance. But it's this -- the unusual mating system of Weddell seals -- that's the focus of this research.

WAAS: The males will actually bite at one another's genitals, and in the water you'll see them spinning around, trying to get at one another's genitals.

COUKELL: So this male that's on top of the ice --

WAAS: This is a loser. (Laughs.) He's probably not going to reproduce this season. The guys that are down there are the ones that are really going to be reproducing.

COUKELL: So there's more than one down there, though?

WAAS: Oh yeah. Whole little territories. You know, there'll be an area like this that'll be the territory of one of the males here. Then adjacent to it, almost like in song birds, there'll be another territory adjacent to that that's defended by another male. And then further down the crack, another territory.

COUKELL: The males stake out and defend small territories under the ice around the access holes, so they can mate with the females when they leave their pups and enter the water to feed. The question for the scientists is do the best fighters make the most successful lovers? Mark Hindell is a zoologist from the University of Tasmania in Australia.

HINDELL: What we want to know is whether or not it's actually the territory holders that actually do father all the pups. In previous years we've been checking them and mapping those territories, and relating how many offspring different males have to see if there's some sort of tradeoff -- size of territory or amount of energy they spend or whatever -- in terms of the offspring they have. And this year we're coming back now to find out the answer to that question.

COUKELL: To conduct the paternity test, the scientists take tiny skin samples from the seal pups. DNA from the samples will be compared with DNA taken from the males last year.

[SOUNDS OF SEALS]

COUKELL: Here on top of the ice, the seals are ungainly and not very musical. But even through six-and-a-half feet of ice, we can hear eerie calls telling us that down below is another story.

[SOUNDS OF SEALS UNDERWATER]

WAAS: Well, they make an extraordinary number of different sounds. I think somewhere between, say, about 25 or 30 different sounds.

COUKELL: Joe Waas has been recording this underwater symphony. He says beautiful though it may be, it, too, is part of the competition for breeding success.

WAAS: There are certain sounds that they'll only do below the ice. The males have certain types of calls that the females won't use. Like they have this very long, sort of downward trill [CUTAWAY TO SOUND] and we think that that's associated with attracting females to the territory, so the males can actually tell the females how big they are. And high quality large males would be potentially preferred by females. [SEAL SOUNDS] And the calls are also used -- like that trill call, it's thought that it's used to sort of defend the area against other areas. Again, and you can sort of tell the other males how big you are by how deep in pitch their calls can actually go. [MORE SEAL UNDERWATER SOUNDS]

COUKELL: By examining the calls and looking at the DNA, the scientists can find out about the mating habits of the seals. Mark Hindell says this, in turn, could lead to a wider understanding of animal behavior.

HINDELL: Well these guys are interesting because they're an anomaly. They're sort of an outlaw. And not just in seal mating systems, but in mammalian ones. And it's always very instructive to compare how different systems work and the different environments that they work in, because that tells us something about the conditions that are required for certain things to evolve.

COUKELL: After a few hours, Mark Hindell and Joe Waas return to their camp to warm up with a mug of tea. As in each of the previous three years, they'll remain on the ice for several more weeks. Then they'll pack their camp for the last time, returning to the land of trees and universities to analyze their findings.

[SEAL SOUNDS, UP AND UNDER]

Perhaps, though, a trace of this seal song will stay with them as a reminder of the beauty and complexity of life in this harsh place. For Living On Earth, I'm Alan Coukell, from Ross Island, Antarctica.

[MUSIC]

 

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