Bubble Gum Walrus
INTRO: Marine mammals have evolved a number of strategies to stay warm in the frigid Arctic. Seals have short dense fur over a layer of blubber, while polar bears have thick, long fur that traps air close to their skin. But walrus have chosen a different path to staying warm, as Doug Schneider reports in this week's Arctic Science Journeys Radio.
From a vantage atop a cliff overlooking the Bering Sea, I saw hundreds of walrus crowded onto rocky beaches below. An amazing sight, male walrus gather here each summer to rest and shed their skin. As walruses clamored and stumbled over each other, my eye caught something odd gliding beneath the ocean surface, heading toward shore. Seconds later, it showed itself to be another walrus. But this one was very different. Rather than brown in colorlike the ones on the beachthis one was a pale gray, almost white. After a few minutes ashore, the walrus turned the color of bubble gum.
With me at the time was Dr. Sue Hills, a marine scientist from the University of Alaska Fairbanks. She told me this walrus had recently returned from feeding far out to sea. The cold water, she said, made their skin turn pale. To learn more, she suggested I talk to Kathy Turco, who'd done her master's degree on walrus a decade ago.
These days, Kathy Turco is a laboratory technician at the university. She also runs a sound recording business and travels extensively, collecting sound effects for Hollywood movies, television specials and radio programs. I asked her about Round Island's strangely colored walrus.
TURCO: "When they get onto land amidst other walruses, and they are able to be in the air, color comes back to them. The bubble gum walrus you're talking about is one that's been on land, who is pink."
Turco spent an entire summer on Round Island observing walruses to understand how they've adapted to an ocean that can be near freezing and air temperatures that routinely dip to well below zero.
TURCO: "Well, if that's the case then their skin cells are able to tolerate very low temperatures. If our skin is exposed to very cold temperatures, we get frostbite and cells die. Walrus skin has a very high tolerance for cold temperatures without the cells actually dying. How do they do that?"
Since the walruses couldn't be approached or handled, Turco had to gather data from a distance. She used a specially designed heat-sensing gun. The gun measured the temperature of an area one foot in diameter, from a distance of 60 feet.
TURCO: "What warms up firsthis head, his neck, his flippers? So that's what I was trying to get a handle on by pointing my gun at different parts of their body."
She also examined skin samples from walruses taken by Eskimo hunters. She thought walruses would be much like seals and other pinnipeds that regulate heat loss by turning blood flow on and off to clusters of vessels near the skin surface, where heat loss would be greatest.
TURCO: "There's a hypothesis that some seals have what are called anastamosesarterial venous anastamosesthat some animals use to shunt blood back to the body as a way to conserve heat. It's a way of shutting down peripheral blood flow. So I wanted to get at whether there is a layer of blood vessels that allow them to shunt blood back and forth. And actually what I discovered was that they don't have these anastamoses. Or at least from my work, I couldn't find these anastomoses."
While Turco didn't learn exactly how walrus regulate heat, she did narrow the list of possible physiological mechanisms. She believes walrus probably regulate heat loss not by shutting down blood flow to the skin, but by slowing it. She says walrus's thick, tough skin helps by shielding it from the elements.
TURCO: "It's very thick skin. It's comparable to rhinoceros skin. When you cut into it, it's like cutting into a tire. Then there's a layer of blubber beneath that. The idea is that if you can allow the outside layer of your body to cool, you create a temperature gradient from your skin to your inner core, and there's less heat loss that way."
Turco says walrus most likely constrict muscles around blood vessels close to the skin to slow blood flow and conserve heat during cold periods. When they're hot, they dilate them, letting blood reach the skin and letting body heat escape. But this theory has yet to be proven, and scientists still don't know exactly how skin cells keep from freezing when blood flow is restricted. And of course, the walrus aren't telling.
OUTRO: This is Arctic Science Journeys Radio, a production of the Alaska Sea Grant Program and the University of Alaska Fairbanks. I'm Doug Schneider.
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Thanks to the following individual for help preparing this script:
Arctic Science Journeys is a radio service highlighting science, culture, and the environment of the circumpolar north. Produced by the Alaska Sea Grant College Program and the University of Alaska Fairbanks.
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Related Web sites
Marine Mammals of Alaska (book)
Pacific Walrus (U.S. Fish and Wildlife Service)