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PRI's Environmental News Magazine

For Elephant Seals: A Harem of Valentines

Air Date: Week of February 6, 1998

Northern Elephant seals spend most of their time at sea. But, from December through March, they come ashore to mate and raise their pups on a number of islands off the coast of California and Mexico. Competition is fierce among the males. Each year only a few will win the right to breed and take charge of a harem of females. Jim Metzner traveled to Ano Nuevo island, near Santa Cruz, to bring us this story of sex, violence and scientific mystery.

Transcript

CURWOOD: Northern elephant seals spend most of their time at sea. But from December through March they come ashore to mate and raise their pups on a number of islands off the coast of California and Mexico. Competition is fierce among the males. Each year only a few will win the right to breed and take charge of a harem of females. Jim Metzner traveled to Año Nuevo island, near Santa Cruz, to bring us this story of sex, violence, and scientific mystery.

METZNER: Think about a very large creature, the size of a hippopotamus, 2 tons worth, 16 feet long, and you've got a sense of what an elephant seal looks like.

(Surf, and an impact sound)

METZNER: The large male seals use this sound as part of their arsenal of intimidation to become the alpha male. Bernie LeBoeuf, a biology professor at the University of California in Santa Cruz, is one of the world's leading experts on elephant seals. He says that after issuing vocal challenges to rivals, the 2-ton bulls act like boxers, feinting, parrying, and then striking out with their large teeth into the necks of their opponents.

LEBOEUF: They're very bloody affairs. Males get injured; indeed, a few males will get killed in a fight. The upshot of all the fighting is that the males who win emerge in a social hierarchy, and it's the highest ranking males only that do all of the mating with all of the females in attendance, which maybe hundreds, in some cases thousands.

METZNER: Sex, violence, power struggles. It was enough to keep even the most jaded scientists happy for a while investigating elephant seals in the 3 or 4 months that they spend on land. But the rest of the year the seals are at sea, and Dr. LeBoeuf and his colleagues had the idea to attach depth time recorders to the seals to monitor their activities. What the scientists discovered surprised them. It turns out that elephant seals are prodigious divers. They're able to spend up to one and a half hours underwater and dive to nearly a mile in depth. They'll surface for a few minutes, dive again, and keep this up round the clock for 8 months at a time.

LEBOEUF: These animals are able to dive very long in part because they lower their metabolic rate. It would be like lowering the thermostat on your central heating, which would then enable you to parcel out a limited supply of fuel for a much longer period of time. Well, essentially, that's what these animals are doing with a limited supply of oxygen. Inevitably, they spend a brief period of time at the surface, leading you to believe that they never really were stressed by shunting oxygen from peripheral organs like the liver and the kidney to the heart, brain, or lungs. It's a phenomenal situation.

METZNER: Scientists at the Scripps Institute of Oceanography have recently reported that elephant seals and other deep-diving animals have high levels in their blood of a protein called myoglobin. By helping to store oxygen in muscles, myoglobin gives the seals the energy they need to swim without breathing for long periods of time. Not needing to take a lungful of air to great depths enables the elephant seal to avoid another pitfall of diving: the bends. The bends results when air under pressure causes nitrogen to bubble up in the bloodstream. For humans this can be fatal. The elephant seals avoid it by collapsing their lungs.

LEBOEUF: At about 40 meters the lungs completely collapse, and they are collapsed throughout the dive until the animal comes back to about 40 meters of depth. So, in a sense, the elephant seal, who is spending 8 to 10 months of the year at sea, 90% of that time the animal is underwater, and it is deeper than 40 meters, and during that period its lungs are entirely collapsed. So you could say that for most of the year the elephant seal lives with its lungs collapsed.

METZNER: Among the elephant seal's mysteries are: how is it able to reinflate its lungs so quickly? How does it slow down its metabolism? How do its organs survive on such low levels of oxygen? And, for goodness sake, when does it sleep? The answers could be of great importance for the treatment of lung disorders, the preservation of human organs, and the prevention of diving sickness, just to name a few applications.

(Seal makes impact sounds)

METZNER: From the scientists who are unraveling its secrets, the elephant seal gets some well-deserved respect. For the seals ashore at Año Nuevo, though, respect is reserved pretty much for the alpha males, who until early March have something to snort about.

(Surf and impact sounds)

METZNER: For Living on Earth, I'm Jim Metzner.

 

 

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