The technique involves fastening miniature video cameras to animals, thereby turning them into unwitting cameramen. The cameras, designed to detach from animals on a timed release, cause no long-term harm to animals.
But sharks are not always the most cooperative coworkers.
"In fact there was an attack while we were out there," Greene told National Geographic News. "It was not at all related to our work. It happened on the other side of the island and was most likely a mistaken identity."
When a shark is released with Crittercam attached, the fun begins. "We let it go and track it with an ultrasonic pinger that emits a signal from the camera," Greene said. "We can put a receiver underwater and listen to where the shark is, and track the animal. After two or three hours the camera will pop off and it will float to the surface, where we can track it with VHF telemetry tracking."
As is often the case when wild animals and expensive equipment are involved, there were some tense moments.
"We had some problems with the sharks swimming in and out of the reefs. A lot of times we'd lose the signal," Greene said. "We'd panic about losing the camera, because in this area it would just roll out to the middle of the Pacific and we'd never see it again. In fact, that happened to one of them."
But the unique perspective of Crittercam provides important information that makes the work and the anxiety pay off.
Improving technology like satellite tracking tags allows researchers to look at animal behavior on a much larger scale over a longer period of time. Crittercam allows scientists to observe important aspects of behavior that would otherwise be impossible to witness. The two work effectively together.
"At the same time we put on the Crittercam, we attach acoustic tags," said Lobel. "By tracking we can determine how much time a shark physically spends in a certain area. With the cam, we wanted to see more of its behavior while it's in an area."
"One of the things we found with the cam was that when this shark was cruising in areas of interestit wasn't alone. As many as 20 other sharks were with the one we were tracking," Lobel said. "So when we can say it wasn't alone, it was with a group of 20 sharks, we know a heck of a lot more about what's going on with that species. It gives us much better insight into their behavior."
Another cam deployment provided a new look at a long-standing Johnston tradition. At the island's west-end wharf, food leftovers are dumped each day into the outgoing tide.
"Predictably there are sharks and tons of other fishes feeding on this. The animals have learned as others do to expect a daily feed," Lobel said.
The scientists have long observed the feeding from shore, watching a group of perhaps 30 to 40 sharks that became the basis of a population estimate.
"Well, another thing we learned with Crittercam is that not every shark is at the surface feeding at the exact same time," Lobel said. "While we're looking at the surface the Crittercam is down at the bottom in the deep water with another group of 20 to 30 sharks who are ignoring the whole deal."
"We know that they don't eat every day in the wild. I can't tell that these sharks had full stomachs, but that might be a guess. Certainly if we're going to base a census on what we see on the surface, it's a gross underestimate," Lobel said.
Such discoveries offer a tantalizing glimpse at the important information and dramatic images future Crittercam deployments could deliver.
At Johnston Atoll the research continues, as does the site's dual role as both military facility and wildlife refuge. That is until next year, when the U.S. military is set to leave the facility in the hands of U.S. Fish and Wildlife Service.
More Shark Resources on Nationalgeographic.com
Nurse Sharks: Key to Anthrax Diagnosis, Treatment
Underwater Photographer On Swimming With Sharksincludes two photo galleries
Shark Season: Hazard or Hype?
Asian Shark-Fin Trade May Be Larger Than Expected
North Atlantic Sharks on Sharp Decline, Experts Say
Satellite Tags Keep Track of Great White Sharks
Shark Gives "Virgin Birth" in Detroit
Shark-Soup Boom Spurs Conservationist DNA Study
Shark "Photo of the Year" is E-Mail Hoax
Great Whites May Be Taking the Rap for Bull Shark Attacks
Crittercams Provide Insights into Nurse Shark Behaviorincludes photo gallery
Researchers Tag Sharks to Study Breeding Habitsincludes photo gallery
Scientists Study Nurse Shark Mating Habitsincludes photo gallery
Jaws Author Peter Benchley Talks Sharkshear him read from his new book
Do Hammerheads Follow Magnetic Highways in Migration?
Shark Nursery Yields Secrets of Breedingincludes photo gallery
South Africa Rethinks Use of Shark Nets
Sharks Falling Prey to Humans' Appetites
Satellites Clear Up White Shark Mysteries
Are People Eating Sharks Out of Existence?
SOURCES AND RELATED WEB SITES