Sharks Help Scientists Study Pacific Nuclear Test Site
for National Geographic News
|August 11, 2003|
Nuclear weapons, Agent Orange, and mustard gas aren't normally associated with environmental protection. Yet on a remote Pacific atoll they've been indirectly responsible for safeguarding a thriving coral reef ecosystem. The U.S. military has maintained a presence on Johnston Atoll since before World War II. Over the years, it's housed a nuclear testing site and, more recently, a facility for the destruction of chemical weapons.
Because of these activities, Johnston Atoll's marine environment has been spared many of the pressures that affect similar habitats worldwide. A landing strip on the tiny island makes it resemble a floating aircraft carrier. But underwater, it's a different story.
"It's a very pristine atoll," said Phillip Lobel, a Boston University professor who has conducted military-supported environmental research at the atoll for 20 years. "It has not been subject to commercial or even much recreational fishing, because, until recently, as long as the weapons were there, the military was very strict about anyone coming too close to the atoll."
Enforcement, so often a problem in the management of marine resources, was not an issue at the well-guarded facility.
"Underwater, the island's really in pretty gorgeous condition," Lobel said.
Still, many question the impact of the island's chemical legacy, one that includes a plutonium landfill that's spurred debate between environmentalists, the military, and the U.S. Fish and Wildlife Service.
Johnston Atoll is a remote spot lying some 500 miles (800 kilometers) from the next closest landfall at French Frigate Shoals in the Hawaiian Islands.
Part of Lobel's research is an ongoing attempt to gauge the environmental impact of the atoll's weapons-testing legacy. The atoll's abundant shark population has become an important part of the research picture. "Our bigger battle is to determine what really needs to be done in terms of environmental protection. This shark work is a direct part of that," Lobel said. "In some animals we see measurable levels of PCBs and dioxins. So we want to know, how are they possibly acquiring this? Is it a threat?"
Several species of shark inhabit the reef. But the one Lobel and colleagues research most closely is the grey reef shark (Carcharhinus amblyrhynchos).
"During the shark study we're looking at bio-accumulation of contaminants, PCBs, and other things," Lobel said. "These are top-level predators, and we're very interested in knowing where they go, where they feed. We'd like to know if they might concentrate their activities in certain areas that have fewer or more contaminants. That's part of what the Crittercam research was for."
As part of the site shark research, Greg Marshall of National Geographic Television was on hand to employ "Crittercam" technology, with a team including Patrick Greene. The Crittercam was invented by Marshall, a marine biologist and Executive Producer/Director with National Geographic Television. Marshall has spent over a decade developing the crittercam program, which is currently in use on research sites around the world.
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.
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