Ocean Watch

Monday, February 24, 1997

Monk seals make movies
with the ‘critter cam’

One of the major problems biologists face in protecting our critically endangered Hawaiian monk seals is lack of knowledge. When seals are in the water, where do they go? What do they eat? How do they find it?

The scarcity of facts, particularly about the eating habits of monk seals, is frustrating for managers who need to know more to help the animals' plummeting populations.

At French Frigate Shoals, the number of seals has dropped from about 800 in 1989 to about 400 currently.

Recently, though, there's been a breakthrough in underwater seal study: Workers have devised a way for monk seals to film themselves.

National Geographic photographer Greg Marshall invented the sophisticated system, nicknamed the "critter cam." Last summer, with National Marine Fisheries Service biologists, Marshall attached a 4-pound camera to the back of each of eight male monk seals at French Frigate Shoals.

To do this the team sedated the chosen seal. Then they epoxied the camera housing onto the seal's furry back, just behind the neck.

When the seals woke up, they headed for the ocean and the cameras started rolling.

Daylight and saltwater immersion triggered filming, which was timed to run for 11/2 minutes every 15 minutes. After the three-hour film ran out, the team found the seals and removed the cameras.

Watching the subsequent footage feels like a breakneck ride on the back of the seal itself. But besides the thrill of getting a seal's-eye view of the world, researchers now know something about what these marine mammals do when they disappear beneath the water's surface.

Sometimes the seals are simply napping. The cameras recorded seals sleeping in caves as deep as 250 feet. After about five minutes, the seal would swim to the surface, take a breath or two and head back down for more snoozing.

Some camera-bearing males also spent time stalking and harassing female and immature seals. One adult male was recorded chasing, bellowing at and trying to mount a juvenile seal.

Other times, monk seals forage for food. Everyone expected this. But it was the seals' style of hunting that came as a surprise.

Never did seals chase fish swimming in the open. Sometimes whole schools would pass by without arousing the slightest interest of the seal.

Instead, the films showed seals cruising over sandy or rocky bottoms as deep as 300 feet. Occasionally, the animal would turn over large, flat rocks with its snout, presumably looking for eels, octopus, sand-dwelling fish or invertebrates.

One time a seal caught and ate a razor wrasse. Another snatched a triggerfish. A third ate an octopus. A fourth seal rooted in and around an empty lobster trap.

Sometimes, gray and Galapagos sharks accompanied the seals during this rooting. Other times as many as 30 jacks tagged along, probably waiting for a fish or invertebrate to be flushed out by the seal's stirring.

This information may not seem earth shattering, but in the world of monk seal research, it's a gold mine. And it's just the beginning.

This summer the critter cam team is planning to attach cameras to seals again, possibly in another area of the refuge.

By comparing films, researchers may find clues to the reasons behind the French Frigate Shoals' population decline.

These critter cams belong to the National Geographic Society, which means that everyone will likely get to see some of this fantastic film work in one of their upcoming nature shows.

Watch TV listings for a National Geographic special on seals. In it our own Hawaiian monk seals will be the stars, carrying the cameras that not only entertain but may also help save the species.