To Seal with Love

By Julie Zeidner Russo

They may not use spears, but seals have a variety of clever ways to go hunting. Now researchers have a unique perspective of their behavior under the Antarctic ice thanks to a novel video system and data recorder worn by the seals like pill box hats.

Several Weddell seals in McMurdo Sound were enlisted for the audiovisual experiment by a joint research team headed by marine biologist Dr. Randall Davis of the Texas A&M University at Galveston. Dr. Davis' co-investigators on the project were Drs. Lee Fuiman of the University of Texas at Austin, Terrie Williams of the University of California at Santa Cruz and Ian Boyd of the British Antarctic Survey.

Not only did the research reveal aspects of seal behavior that were previously unknown, but revealed the previously unstudied behavior of other fish populations.

The video cameras worn by the Weddell seals recorded the seals foraging beneath the ice in ways that had never been observed before. Using the under-ice surface for backlighting, seals stalked large Antarctic cod to within centimeters of the fish without startling them. At times, it seemed like their pursuit of the cod was done more out of curiosity than aggression, Dr. Davis said. Not only did the research reveal aspects of seal behavior that were previously unknown, but revealed the previously unstudied behavior of other fish populations. The seals also blew air through their nostrils into sub-ice crevices to flush out smaller fish or pursue them into the platelet ice, said the marine biologist. Results of the study were published in the journal Science in January.

Seals wore the novel video system and data recorder like pill box hats. The near infrared light of the camera was designed to be invisible to the Weddell seals, as it is to humans, to prevent any alterations in normal behavior of the marine mammals and their prey, Dr. Davis said. For the first time, this enabled researchers to observe their underwater behavior, track their movements in three dimensions, and simultaneously record data on their environment. Photo by Lee Fuiman

The video cameras worn by the Weddell seals recorded the seals foraging beneath the ice in ways that had never been observed before. Seals stalked large Antarctic cod to within centimeters of the fish without startling them. Photo by Lee Fuiman

"Unlike terrestrial animals that we can observe with a spotting scope," Dr. Davis said. "The behavior of marine mammals that spend up to 90 percent of their time at sea is very much a mystery. Direct observation of marine animal behavior using SCUBA, fixed-location cameras, remotely operated vehicles and manned submersibles provides only fleeting glimpses of highly mobile species."

Dr. Davis received support from the National Undersea Research Program's West Coast and Polar Regions Center at the University of Alaska Fairbanks to design and fabricate a small video/data recorder that could be attached to free-ranging marine mammals to observe their underwater behavior, track their movements in three dimensions, and simultaneously record data on their environment. The near infrared light of the camera was designed to be invisible to the Weddell seals, as it is to humans, to prevent any alteration in normal behavior of the marine mammals and their prey, Dr. Davis said. The newly developed technology was used successfully during more than 57 hours worth of underwater recordings between October and December of last year as part of a National Science Foundation study of the foraging behavior of deep diving Weddell seals in Antarctica.

Scientists took advantage of the natural history of Weddell seals to observe them beneath the four-meter thick frozen ice where they would normally be out of sight. The average 400 kg. Weddell seal, named after the famous British Antarctic explorer James Weddell, are highly adapted to hunting. They dive through naturally occurring cracks and holes of ice to depths averaging between 100 to 350 m for 25 minute stretches, but must pop back through these ice crevices to breathe again. This makes them relatively easy animals to track, Dr. Davis said.

"Weddell seals are wonderful animals to work with," Dr. Davis said. "They're very mild mannered since they have no natural land predators. Unlike ring seals in the Arctic that have to deal with polar bears and (human) hunters, Weddell seals usually just ignore you. It's very rare that they would bite."

The researchers drilled a hole through the ice in a spot where there are no naturally occurring holes and built a climate controlled laboratory with access to the hole above it. Four adult Weddell seals released into the hole would dive as deep and long as they liked, but had to come through the drilled hole to breathe. When the seals came back to float in the hole while sleeping, the researchers would remove and reload video and data recorders from their headdresses.

In McMurdo Sound, Antarctica, the researchers drilled a hole through the ice in a spot where there are no naturally occurring holes and built a climate controlled laboratory with access to the hole above it. Seals released into the hole would dive as deep and long as they liked, but had to come through the drilled hole to breathe.
Photo by Lee Fuiman

"The technology is opening up completely new windows on these animals," Dr. Davis said. Researchers can now compute the virtual environment of the Weddell seal plotting its animated three dimensional dive path, the exact location of the prey, and all the marine mammal's interactions below Antarctica's ice-covered sea.

In the future, Dr. Davis anticipates smaller technology that could be used to track sea lions, penguins, and eventually tunas, sharks, and sea turtles. "This is just the beginning of what will offer some of the most exciting biological information yet to be uncovered," Dr. Davis said.

Additional information about this project can be found at http://www.utmsi.utexas.edu/staff/fuiman/antarctica/. The participating principal investigators are as follows: Drs. Randall Davis, Texas A&M University @ Galveston, Lee Fuiman, University of Texas @Austin, Terrie Williams, University of California @ Santa Cruz, and Ian Boyd, British Antarctic Survey. Funding for the project was provided by the National Undersea Research Program and the National Science Foundation.

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