2001 Antarctic Expedition
The Foraging Biology of Weddell Seals
Notes
from the Field
(from Terrie M. Williams, Ph.D.)
text and photos copyright to T.M. Williams
The Weddell seal is a large phocid seal that lives in the
Antarctic.
Temperatures often get so cold that it can even freeze the seal's
whiskers. (Photo
by T.M. Williams)
WEEK 3 – WEDDELLS AND WEATHER
Seals
and Scientists on Ice
The primary goal of our expedition for this week is to locate the Weddell seals that will be studied during our experiments. To accomplish this task, there are several obstacles that the research team must overcome. First, the seals and ice cracks are not in their usual places (see Week 2). That means we will have to conduct many more surveys on the sea ice to find Weddell seals. Second, the weather will affect the movements of both the seals and ourselves. Extremely cold temperatures and blowing snow periodically force everyone to take shelter.
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Weddell seals haul out on top of the ice to sun themselves when the weather allows it. As shown in the picture on the left, they often look like giant sausages in the snow and are easy for our research team to find. (Photo by T.M. Williams) |
| If it is too windy, snowy or cold the seals seek shelter in the calm water under the ice. During those times the seals will poke their noses out of small holes in the ice in order to breathe. Unfortunately, this makes the seals difficult to find during our surveys. (Photo by R.W. Davis) |
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Underwater view of a Weddell seal breathing at an ice hole. (Photo by R.W. Davis)
Because breathing holes in the ice are critical for the seals' survival they constantly guard them from freezing and from other seals. While breathing in the ice holes, the seals keep watch in the water below for other seals that might try to bite their flippers and then steal their breathing hole.
Weddell seals are also equipped with special teeth that enable them to keep their breathing holes from freezing shut. The front canines of the Weddell skull protrude forward, giving the seal a "buck tooth" appearance. These huge teeth are used like the prongs of steel rake to scrape ice from the side of the hole. Using a behavior called "reaming" the seal can quickly widen the size of an ice hole by shaking its head back and forth while scraping its teeth along the ice. Eventually, the hole will grow from snout sized to body sized and allow the seal to once again haul out on top of the ice.
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The teeth and skull of the Weddell seal are
highly specialized. Note the protruding front teeth that
are used to ream the ice. (Photos by T.M. Williams)
One of the biggest challenges when working and living in the Antarctic is the weather. Scientists and seals are acutely aware of the temperature, wind and snow conditions. It can mean life or death, especially if you are not prepared.
Blowing snow and exceptionally low temperatures prevent us from conducting our surveys for several days this week. When wind chill temperatures drop below -57oC (-70oF) it is too dangerous to drive the snowmobiles that we use during the seal surveys. The added wind from riding on a snowmobile can easily freeze body parts. Another BIG mistake that can be made at these temperatures is touching anything made of metal. For example, taking pictures or videos in the Antarctic can quickly freeze your fingers because you often have to focus the small buttons with your gloves off. Sun glasses used to protect your eyes from snow blindness can freeze to your face. This is also not the place to have pierced ears or pierced anything- metal touching skin immediately freezes causing instant frostbite!
Even the seals seem to realize that it is too cold and are no where to be found.
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Lee Fuiman, one of our expedition members, walks through the blowing snow. Although it is summer in the Southern Hemisphere, it definitely feels like winter when you work in Antarctica. Yesterday the temperature high was -20oC (-4oF) and the low was -27oC (-17oF). With the blowing winds the wind chill makes it feel like -57oC (-70oF) on your skin. These temperatures are nearly three times colder than the freezer in your house. (Photo by R.W. Davis) |
Another danger is the speed with which weather changes in the Antarctic. The rule of thumb when you are on the sea ice near McMurdo Station is, "75 minutes to reach shelter if White and Black Islands disappear". These two islands sit in the path of Herbie Alley. This is the direction that high winds and blowing snow (called Herbies) usually come from. If the islands disappear in a white cloud of blowing snow you have a little more than an hour to find shelter from the storm. Naturally, our expedition team members keep a wary eye on White Island and Black Island whenever we are conducting our seal surveys.
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These photos of
the National Science Foundation Chalet at McMurdo Station illustrate how
quickly the weather can change. They were taken
within 30 minutes of each other. When blowing snow reduces
visibility it is called Condition 1 (shown on left) and we are not allowed
to travel on the sea ice. Unlimited visibility is called Condition 3
(shown on right). (Photos by T.M. Williams)
A Discovery
Later in the week the weather clears and 10 Weddell seals haul out by the crack near our camp. We try an experiment with an infrared thermal camera that we have brought on the expedition. We want to know how cold Weddell seals get when they lay out on top of the sea ice. The camera is able to detect surface temperatures of the seals and show us how much heat is being lost. We suddenly discover the unexpected. Weddell seals on the ice are not cold - they are HOT. Our measurements show us that the bodies of the seals are so hot that they melt the snow beneath them into seal shaped tubs. The parts of the seal's body exposed to the sun are much warmer than the surrounding air temperatures.
The pictures above are conventional and infrared images of the same Weddell seal that has been lying in the sun. Red and orange denote hot areas and blue shows cold areas of the seal. Note the cold, snow covered whiskers and the hot eyes. This seal was bitten on the muzzle by another seal (probably in a battle over an ice hole). The wounds show up as orange hot spots on the muzzle in the infrared picture. (Photos by T.M. Williams)
Based on these observations, we wonder if laying in the sun is one way that Weddell seals can keep warm in such a cold environment. The research team is excited about these new discoveries and decide to use the infrared camera in our upcoming experiments with the diving seals.
Next week - The Laboratory on Ice
Happy Halloween From Weddell World
(Photo by R.W. Davis)
You
can write to members of our Research Team at williams@biology.ucsc.edu