Scientists Use Seals to Videotape Deep Sea Fish

Here's a challenge for a marine ecologist: Find out what it's really like to survive as a seal or a fish in the dark, cold, forbidding waters beneath Antarctica's floating ice fields.

It would be helpful to find a camera crew willing to strap on a bunch of equipment and dive hundreds of feet below the ice while snapping pictures of seals zipping through the water toward their prey. The crew would also need to keep a record of all sorts of things like water temperature, depth and location.

And, of course, they would need to survive the ordeal and return the equipment and all the data recorders to the scientist. That's an assignment that's not likely to appeal to very many photographers, so Lee Fuiman of the University of Texas and a few colleagues came up with an alternative. They recruited a bunch of Weddell seals to serve as their film crew.

The result, Fuiman says, is an extraordinary look at survival in the trenches beneath the ice that blankets Antarctica's McMurdo Sound for most of the year.

Star Cameraseal Ally McSeal

Fuiman, Randy Davis of Texas A&M, Galveston, and Terrie Williams of the University of California, Santa Cruz, have completed the first three-year phase of the project, sponsored by the National Science Foundation, and they have moved on to a more complex phase.

They couldn't have done it without the help of seals like the one with so much personality she was dubbed Ally McSeal, who became so fond of her collaborators that she returned to their base camp several times, apparently just to say howdy.

The equipment was attached to rubbery material like that used for wetsuits, and the rubber was glued to the pelt of the seals. But since the equipment, consisting of sensitive video cameras and all sorts of instruments, was worth thousands of dollars, and since all of the data and images would be stored on board the animal, the researchers were kind of anxious to come up with a way to guarantee that they would be able to recover it all.

The scientists knew they wouldn't have any trouble catching a seal, because seals have no natural predators during the Antarctic spring, when the seas are covered by ice that keeps killer whales away.

"Getting close to them is quite easy," Fuiman says. "You can walk right up to them."

Right, but how do you make sure they'll come back at the end of the experiment so you can collect your instruments and data? You make sure they don't have any choice.

One Exit Only

In the first phase of the project, the scientists searched the ice field for areas that had no holes or cracks where seals could surface and breathe. Then they drilled a hole in the ice and set up their laboratory over the hole.

"Then we would go out and catch a seal, bring it to our laboratory, put the equipment on it and release the seal into the hole," Fuiman says. That left the seal free to resume its normal activities, including searching for food. But in order to breathe after diving for anywhere from 20 to 70 minutes, the seal needed to surface. And there wasn't any place to surface other than the hole beneath the scientists' lab.

In all, 15 seals took part in the experiment, diving to depths of more than 1,000 feet, where water pressure was so great it squeezed their lungs down to a fraction of their normal size. But in the end, all the seals had to return to the lab if they wanted to take that essential breath of fresh air.

The scientists ended up with nearly 200 hours of videotape, most of it black because the cameras ran continuously as the seals prowled through the deeper waters. But every now and then, a flash appeared in the darkness. By examining that flash, frame by frame, the researchers were able to tell if the flash was a silverfish, a six to eight inch long fish that nearly everybody eats in Antarctica, or a toothfish, a big fish that can range up to six feet long.

The images are not "TV quality," Fuiman says, because there's so little light available that only black and white images could be acquired. But they served the essential function of letting the researchers know exactly what kind of prey the seals were after.

The data revealed a few surprises. Both species, which are critical components in Antarctica's food chain, roam over widely ranging depths. Silverfish, for example, were found as deep as 1,132 feet.

Independent Researchers

One of the questions confronting the scientists is how the seals track down their prey, and there was at least one clue in the data. Some scientists believe seals can smell their prey, and even follow that scent through the water, and others think the seals probably use sight. "You and I are very visual organisms, and our first guess is that they are using sight," Fuiman says. "I'm not quite ready to jump to that conclusion yet."

However, the videotape shows that in a number of instances, the seals came up from below to attack the silverfish, suggesting that light penetrating through the ice above may have allowed them to see the prey.

That's one of the questions that the researchers hope to answer in the current phase of the project. Emboldened by their success, the scientists abandoned their hole-in-the-ice approach and began strapping their equipment on seals found in their natural environment. It was a bit risky, because there was no guarantee that they would be able to find the seal later, but it would allow the seals to interact with other seals.

And it all worked out. All of the seals returned to the area, so the scientists could recover their data.

That included Ally McSeal, who perhaps should have been named McPig, because she was seen slurping down at least 100 silverfish during a single dive.

And when it was all over, McSeal "returned repeatedly" to a group of scientists who had set up camp on the pack ice, according to Williams.

Maybe she just wanted to get screen credits.

Lee Dye’s column appears weekly on A former science writer for the Los Angeles Times, he now lives in Juneau, Alaska.