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| A whitetip reef shark at Molokini Crater off the coast of Maui shows a spot pattern vaguely resembling the Hawaiian Island chain. This shark has been sighted by multiple photographers. - PAUL BRADBURY/Courtesy photo |
Understanding the sharks
Zoologist comes face-to-face with predator in the name of science
Almost daily, Nick Whitney comes face-to-face with one of the ocean's top predators -- whitetip reef sharks. For this University of Hawaii zoologist, these encounters are a scientific endeavor, not a foolish pastime.
His mission is to help scientists better understand the behavior of Triaenodon obesus by tagging and photographing these sharks, as well as documenting their movements.
Whitney recently asked recreational divers to submit photos of whitetips for his doctoral dissertation, which examines the sharks' day-to-day and long-term movements. He hopes to discover how frequently whitetips move, where they go and how often they return.
Whitetips can grow up to 6 feet in length and weigh 100 pounds. They are normally found at depths of 25 to 130 feet in tropical waters, including the Red Sea and the Pacific and Indian Oceans.
"The Hawaiian Islands may be a stepping stone for the sharks to disperse from the Indo-Pacific to the Eastern Pacific," Whitney said. "It may also be a central mating location for the species. But we haven't found any evidence proving this yet."
To better understand how whitetips are so broadly distributed, Whitney has been hand-fitting sharks with two types of ultrasonic transmitters.
"One type allows sharks to be continuously followed from a boat for periods of 24 to 48 hours at a time," he said. "The other communicates with bottom-monitor stations which record the presence or absence of the shark, and how long it stays in a given area."
Whitney's capture technique includes surrounding a cave with a net, disturbing a resting shark and getting a rope around its tail.
Once the whitetip is brought to the surface, Whitney and his research team roll the shark on its back to induce a sleep-like stage. Then a minor procedure is performed on the shark's belly, before it is released into the ocean.
"We recaptured one shark, which was tagged 90 days before, and there was only a faint line indicating where the incision was made," he said. "They're amazing healers."
Originally from Michigan, Whitney has been diving among sharks for the last eight years. The first shark he saw was a nurse shark in the Florida Keys. In Hawaii, he works for the Hawaii Institute of Marine Biology and has studied black tip reef sharks, hammerheads and tiger sharks.
While the whitetip is a requiem shark, it does not share the same characteristics of its family members. Easily recognized by its distinct white tip on its back and tail fins, this shark tends to be rather sluggish.
"In general, they're so docile -- so docile that people think they can grab them, pull on their tails and harass them," Whitney said. "They can tolerate divers, but don't like to be harassed. That's what leads to bites more than anything."
Most shark species need to swim constantly to have oxygen pass through their gills, but whitetips have the ability to rest in one place. Usually lying in caves or under coral ledges, they are frequently spotted by divers, Whitney said.
"There's some anecdotal evidence that suggests these sharks maintain a home cave, which they will return to for days, weeks or even years," he said. "Hundred of divers come after these sharks day after day and many get photos of them with underwater cameras. Divers always assume they see the same shark because it's in the same cave over a long period of time. But it isn't."
Local divers and fishermen informed Whitney of a site offshore of Oahu where eight adult whitetips commonly reside. After a year of photographing and cataloging, Whitney determined 23 different sharks actually occupied this site over time.
Whitetips can be identified by the black spots featured on the sides of their bodies. Varying from shark to shark, these spots are used like fingerprints to distinguish and keep track of whitetips.
Hoping to develop a whitetip database, Whitney urged recreational divers to get as many photos as possible. He advised them to focus on the center of the body because it has the best body markings. Yet photographs featuring all parts of the shark's body are considered helpful. Whitney also welcomed old photographs because "whitetips probably live for 10 or 20 years."
Each photo must include the date and location of where it was taken, as well as personal contact information. Send photographs to: <mailto:whitetip@hawaii.edu>whitetip@hawaii.edu or Nick Whitney; Zoology Department; University of Hawaii-Manoa; Honolulu, HI 96822.
So far, 500 photos have been submitted. The most unique photo, Whitney said, shows a whitetip feeding. To view the photographs, visit <http://whitetip.hawaii.edu>http://whitetip.hawaii.edu or <http://www.whitetip.org.>http://www.whitetip.org.
Highly dependent upon coral reefs, whitetips hunt fish, eels, octopi, crabs and other marine life at night. However, they will take hooked or speared fish from fishermen and divers during the day.
"Whitetips are opportunists. We often encounter them with fishing hooks lodged in their mouths, and occasionally with long leaders still attached and running through their gills," Whitney said. "Whenever possible, we try to target these animals and remove those hooks. Often you can still see rusty stains in the corner of the jaw after the hooks have been removed."
Shark populations are declining worldwide because of pollution, habitat destruction and overfishing, according to scientists and conservation groups.
"Sharks are particularly vulnerable to fishing pressures, as they typically show slow growth, high age at maturity and produce only a few offspring per litter," Whitney said. "Thus once the largest, sexually mature animals are removed from a population, it can take decades for the mating stock to replenish and begin population recovery."
Although there are no commercial shark fisheries in Hawaii, Whitney has seen the threats of fishing firsthand. A whitetip shark with $600 worth of transmitters was caught by a fisherman, dragged on the beach and left to die, he said.
"I was very disappointed," Whitney said. "Most sharks are apex level predators. They may be keystone species that directly influence our marine ecosystem structure."
