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› ...I don't think so

Sights and sounds at Weddell World get seal of approval

By Mark Sabbatini
Sun staff

A Weddell seal, above, with a head-mounted video camera feeds on a toothfish. The chart belows shows how the seals’ are tracked. Photo courtesy of Randall Davis (See full-size image>>>)

For the most part they lay around looking like large sausages on the ice, scarcely distinguishable from rocks. At least that’s the surface impression.

But look deeper and it turns out a good part of their time is spent fighting with a gladiator-like ferocity for necessities like food and air, often causing a ruckus that surpasses the volume of any rock concert.

Such is the view from “Weddell World,” a roving field camp near McMurdo Station where a team of researchers has amassed an unprecedented collection of data about Weddell seals during the past five years. Related projects may lead to advances in the human world as well, such as treating heart ailments and dietary deficiencies.

One of the keys to their National Science Foundation-funded project is new technology including small video cameras mounted to the heads of the sea mammals.

“It wasn’t just the underwater video – it was the data being matched to the video,” said Terrie Williams, a biology professor at the University of California Santa Cruz who is one of the project’s three primary investigators. “We’re seeing for the first time what no one else has seen.”

Williams, who made the comparison of sausages with seals at rest, said that accounts for only about 10 percent of their time. Much more of their life is spent hunting and traveling hundreds of meters deep under the sea ice, holding their breath for as long as 80 minutes at a time as they exert themselves.

“Our question is how the heck are they doing it?” she said. “How can they save energy by being a predator?”

Research at Weddell World revealed plenty of answers, such as the seals’ ability to save energy by diving with little exertion. But plenty of questions remain when project members, who departed Antarctica earlier this month and are spending next year off the Ice, seek to return in 2004.

Researchers on the sea ice use a net to capture a Weddell seal that will be outfitted with a camera. Photo courtesy of Randall Davis...(See full-size image>>>)

Randall Davis, the project’s lead investigator, said one of his main goals is to study how seals hunt in dark conditions, either during the winter or under thick sea ice.

“We think vision is important when ambient light levels are fairly high,” the marine biology professor from Texas A&M University said. “Might there be other sensory systems coming in, even when ambient light is high, that we don’t know about?”

Going out strong

This season the team doubled its video data from last year, witnessed the limits of a seal’s eating ability and got a solid read on the role of blubber. One might say they were in Fat City – if that wasn’t the name of a nearby camp conducting research on the digestive process of the mammals.

The home of Weddell World this year was near Tent Island, about 10 miles (16km) north of McMurdo. Finding openings in the ice where seals had surfaced proved to be somewhat of a challenge.

“We were surprised at how ‘tight’ (lack of natural cracks) the ice was,” noted Shane Kanatous, a University of Texas Southwestern Medical Center researcher working on a separate project at the camp, in a journal documenting the season. “It turns out not all of the ice in the sound broke out last year.”

Lee Fuiman, right, and Kate Willis, center, work inside the Jamesway that houses researchers at Weddell World. It is the largest such shelter of any of the remote camps in the U.S. Antarctic Program. Photo by Mark Sabbatini/The Antarctic Sun (See full-size image>>>)

The main building for the camp was a 136-foot (42m) Jamesway shelter, the largest such structure used by any of the remote camps in the U.S. Antarctic Program. Rooms included a kitchen, separate sleeping areas for men and women, and a lab filled with technical equipment and computers linked by satellite to the Internet. At one end was an observation room where a hole was drilled into the sea ice, allowing seals to surface for air and researchers to place in Weddells they caught to observe their behavior.

Weddell World researchers spent the past two seasons observing seals in a free-ranging environment, attaching cameras to them at the camp and allowing the mammals to swim to whatever holes they might choose. The first three seasons their habits were studied in a more restricted environment, with camps located at isolated ice holes too far away from other holes for the seals to reach.

“The seal was able to dive as deep and as long as it wanted to, but it still had to come back to this location,” Davis said.

The free-ranging sites allowed researchers to observe more natural behavior, but also meant more risk and uncertainty after attaching the cameras and other equipment – worth about $25,000 – to the seals.

“This was a big step for us because we essentially were going to give up any control we had of the animals,” Davis said. But he said the chances of losing track of the animals was relatively small as long as the equipment worked, since satellite and VHF radio signals broadcast the seals’ location when they returned to the surface.

Researchers used nets to capture seals on the ice surface – preferably non-pregnant females, who tend to be more docile than males. The seals were then brought by sled to the Jamesway shelter at Weddell World, mildly sedated and hooked up to the cameras.

In earlier years it wasn’t always easy to catch the seals, which can reach lengths of nearly 10 feet (3m) and weigh up 1,100 lbs. (550kg).

A sign greets visitors to Weddell World. Photo courtesy of Randall Davis...(See full-size image>>>)

“We all got whacked by the fins or the back end because we were looking at the head thinking that was the dangerous part,” Williams said.

Experience with the animals and the latest in modern technology played a large role in this season’s success.

Cameras attached to seven seals provided about 100 hours of underwater video this season, Davis said. He said in past years a camera would be deployed on a seal only once, while this year they filmed each seal two to six times.

“What we were trying to do this year especially was to get an adequate sample size,” he said. “The way to do that is to log lots of underwater time, as much as we can.”

Researchers have studied the diving and hunting behavior of seals since the 1960s, primarily using depth and time recorders. But the cameras used at Weddell World proved to be a breakthrough.

The 8mm computer-controlled cameras automatically turned on when a seal dove more than 160 feet (50m) deep and switched off when the mammal spent more than 10 minutes on the surface.

Up to six hours of video could be recorded at a time on digital memory cards at depths of nearly 4,000 feet (1,000m). Other sensors provided continuous data about the seal’s depth, speed, compass bearing, water temperature and flipper frequency, plus sound from the dives. Illumination for the black and white videos came from infrared lights.

“The infrared is invisible to the seals and their prey, so we’re not altering their behavior,” Davis said.

The primary prey for the seals are small silverfish eaten by the dozen and larger toothfish up to six feet (1.8 m) long which may take three hours to consume. More than 1,000 captures were recorded during the five-year study, allowing researchers to generate three-dimensional maps revealing hunting strategies, sensing abilities and other aspects of seal life not possible with previous data recorders.

One map shows a seal making a slow, gradual descent for about four minutes, then changing speed abruptly at about 1,300 feet (400m) in depth and turning to the right, somewhat away from a toothfish being pursued. The seal then drops two meters below the fish and attacks it from below.

The camera mounted on the seal’s forehead allows viewers to see the struggle as it grabs the toothfish by the upper jaw, but “in the end the fish gets away in this case,” Davis said.

A three-dimensional chart shows how Weddell Seals are tracked by head-mounted video cameras. Graphic courtesy of Randall Davis...(See full-size image>>>)

The depth the seals hunted at varied by about 390 feet (100m) by the time of day, apparently due to variations in light intensity, said Lee Fuiman, a professor at the University of Texas who was the third principal investigator at Weddell World.

Generally the captures occurred at 650 to 1,300 feet (200 to 400m) below the surface, but some prey were found at unexpected depths, he said. Previous research by others indicated toothfish would be found below 980 feet (300 m), for example, but “of the 26 encounters we had, only one was below 300 meters.”

It typically takes less than one-third of a second for a seal to catch a silverfish, so those videos need to be analyzed frame by frame, Davis said. He said they learned seals generally eat about 20 silverfish at a time, take a few breaths, then go back down. A seal that ate 30 in one dive apparently exceeded its limits, regurgitating the meal at the surface.

“We don’t know the reason, but there does seem to be some limit there,” he said.

Energy conservation

All those fish add up to a lot of calories – exactly how many is a topic of future study – but it takes a lot to spend hours hunting and swimming in frigid waters. At the same time, the seals also have to make the most of the oxygen in their system as they spend extended amounts of time under water.

Figuring out how the seals maximized their energy resources has been the main focus of Williams’ work at Weddell World. Among the discoveries she’s made is the seals can save anywhere from 10 percent to 50 percent of their oxygen reserves by essentially sinking, rather than swimming, when they descend beneath the surface.

“They don’t need to stroke every time on the descent,” she said.

Digesting their chilled prey requires up to 45 percent more energy than a seal who isn’t feeding, however, and that extra need for oxygen can last nearly five hours, Williams said. That cuts down drastically on the distance they can swim before they need more oxygen.

“The problem is Weddells don’t always have access to air, so we will be looking at their strategies,” she said.

She said seals need to start making a decision about where they intend to surface after about 20 minutes. That gives them enough time to return to their point of origin, if necessary, and alert others who may be competing for the air hole.

“They start to vocalize, warning the others they are coming up and need to take a breath,” she said. Other seals don’t always get out of the way, however, and “sometimes it gets a little rough.”

Energy usage is also a concern on the surface. Williams said researchers brought a portable ultrasound machine to Weddell World this year to analyze skin, blubber and fat, with the blubber layer on one seal measuring 2.6 inches (6.71cm).

Infrared camera readings show a wide variety in body areas where seals lost and retained the most body heat, despite their coating of blubber. Baby seals, who struggle to survive for a number of reasons, have very little ability to retain warmth. Mature seals lose a considerable amount of heat while sunbathing, but for a different reason.

“The seals have to lose excess heat or they would boil in their own insulation,” Williams said.

One remaining mystery is how their racquetball-size eyes stay warm when diving, Williams said. She said high bloodflow in the membrane in the lower part of eye may allow it to retain heat.

Sounds from the Sound

The sights at Weddell World may be impressive, but the sounds at times are absolutely mind-blowing.

The seals perform social, courting and competitive calls at volumes as high as 178 decibels – or about 60 decibels higher than an eardrum-shattering rock concert. Jesse Purdy, a professor from Southwestern University, said Weddell seals have 12 calls with 34 different types of acoustic variations such as pitch, repetition and harmonics. A tape of the seals contains sounds from high-pitched trills to deep thuds that have the rhythm and tone of a bass drum track on a dance club song.

This season’s goal was to find a male seal who would defend the hole and attract females, Purdy said. Within 10 minutes of drilling the hole at the Jamesway, a male who would be nicknamed “Pink 841” surfaced and made his claim to the territory.

Purdy and the other researchers introduced five male seals and nine females into the hole during the season. The interactions with other males were generally competitive, but Pink 841 held his ground.

“You’re going to be hearing a large number of jaw claps and thumping sounds,” Purdy said at the beginning of a taped segment featuring the males.

“These bites don’t sound too bad until you see the animals on the surface and then you realize the game is being played very seriously,” he added, noting some animals had significant flesh wounds.

Interactions with females typically contained a much larger number of chirps and there was a greater willingness of Pink 841 to allow them to surface, Purdy said. The seal proved to be an attractive lure for females, at one point courting three of them at one time.

The sound studies have taken place during the past two years. Davis said the seals may have the ability to hear noises over a six-mile (10km) area, in essence turning the local waters into “a massive party line.”

“Much of McMurdo Sound may be audible to these seals,” he said. “That’s something we haven’t even begun to explore or understand.”

Muscle mania and Fat City

Three other projects involving the study of Weddell seals are taking place in the McMurdo region this year. One is an ongoing long-term effort to record the population dynamics of the area, while the other two involve shorter term research at or near Weddell World that could result in medical findings beneficial to humans.

Kanatous, the University of Texas Southwestern Medical Center professor, is studying the skeletal muscle development of young seals in an effort to learn how the muscles end up highly resilient to low oxygen levels.

“That takes them from land mammals that can’t dive to one of the elite diving mammals of the world,” he said.

His work on the Ice involved collecting muscle biopsy samples from newly weaned pups five to seven weeks old and adult seals. He will use the samples to test the theory that seals begin developing the necessary muscle structure while nursing and continue to develop as they learn to dive.

The muscles may not develop completely until they are several years old, however, meaning they can’t dive as deep for prey as adults, he said.

Kanatous is also studying the seals’ genetic regulation of myoglobin, a highly concentrated hemeprotein. He said learning how seals maintain a normal aerobic metabolism in conditions that are lethal to many animals, including humans, may help lead to the development of muscle protections that could aid in the treatment of ailments such as heart failure.

While Weddell World researchers spent much of the season learning how seals catch their prey, Michael Castellini was a few miles away studying the next step.

“They were looking at how animals caught the fish,” the University of Alaska Fairbanks professor said. “We were looking at how do they process it?”

Observing how seals utilize the marine lipids in their prey, which are rich in omega 3 fatty acids, may provide clues to how humans benefit from consumption of the same lipids, Castellini said. He noted Eskimos and Natives in Alaska traditionally ate a high-fat diet consisting of animals caught in the area, but their health has declined during the past 60 years as Western influence has replaced those items with other fats.

This is the first year of his study. Castellini says he will do most of the analysis on lipid samples he has collected from seals once he is off the Ice, and he will return next year to take different measurements, such as how fast the seals can absorb the lipids.

The long-term population study has been led by Don Siniff of the University of Minnesota, with more than 80 percent of the seals born in the region identified and tagged during the past 30 years. The project’s principal investigator this season is Bob Garrott of Montana State University. Although the group was not directly involved in Weddell World, they did provide some advice, such as telling Kanatous where juvenile seals were likely to be found.

Future years will try to expand on what the Weddell World researchers have discovered. Equipment is also likely to improve: Davis said a next-generation video camera set to debut in a year-and-a-half will be half the size of the ones used now.

Some of the future research is likely to go beyond feeding habits, Fuiman said.

“We’re pretty confident we know what a foraging dive is,” he said. “The challenge is now figuring out what those other dives are for.”

The research was also useful in gathering more information than expected about how the prey of seals live. But Williams said there may also be some interest in focusing more effort on creatures other than seals.

“I think all of us are saying ‘We’ve got Weddell seals. What about the other species?’” she said.