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The Honolulu Advertiser

Posted on: Tuesday, June 14, 2005

Scientists track shark movement

By Jan TenBruggencate
Advertiser Science Writer

During a recent research expedition to the Northwestern Hawaiian Islands, oceanographer Carl Meyer performed surgical procedures on sharks and other predators while hanging over the side of a small boat, inserting electronic tags in their abdominal cavities.

Yanni Papastamatiou, left, and Carl Meyer attach an electronic tag onto a Galapagos shark at Pearl and Hermes Atoll.

NOAA photo by Harvey Walsh

On the same trip, but at the other end of the food chain, marine conservation geneticist Brian Bowen took clippings from the fins of reef fish and samples from corals to conduct studies into their genetic differences.

The two University of Hawai'i ocean scientists, both with the Hawai'i Institute for Marine Biology, conducted their work at five sites in the Northwestern Hawaiian Islands, and although their quarry were different, their goal is the same: to understand how much the animals move between different reefs.

Marine biologist Randy Kosaki of the National Marine Sanctuary Program said the results of the research "will have profound implications" on how the islands are managed. Kosaki was chief scientist on the 25-day scientific cruise aboard the National Oceanic and Atmospheric Administration ship Hi'ialakai.

"Are we really managing one large reef ecosystem or 10 smaller, more fragile ecosystems? If we find that they are very isolated genetically, then we have to be much more careful in how we protect them," Kosaki said.

Meyer and his crew tagged nearly 70 large predators, including 25 Galapagos sharks, four gray reef sharks, 23 ulua, 14 deep-sea snappers, a white-tipped reef shark and a 13-foot tiger shark.

Oceanographer Carl Meyer releases a large ulua that has been equipped with a sonic transmitter which will allow tracking of its movements.

NOAA photo by Harvey Walsh

With the help of graduate student Yanni Papastamatiou and Kosaki, he hooked the fish, brought them up to a small boat, cut a small incision in their bellies and inserted an electronic tag that should keep broadcasting for two years. Then he sewed them up and let them go.

UH marine biologist Kim Holland, a co-researcher on the project, helped develop techniques for radio-tagging sharks and other large marine animals.

It's possible to work with large, potentially dangerous sharks if they are positioned upside-down. The sharks may move a little, but they are in a state called tonic immobility that permits scientists to do their work.

The team also installed a series of electronic listening posts — below-surface floaters, attached to screw-in sand anchors, that record occasional acoustic bursts from the fish transmitters. Each transmitter emits a coded signature, so Meyer will know whether the animals are still swimming and, more importantly, whether they are moving between the islands.

The team has done similar work on sharks in the main Hawaiian Islands. These receivers will recognize any Northwestern Hawaiian Islands sharks that come south, as well as any sharks from the main islands that move north.

"We know that the tigers can make these long-distance movements and we suspect that Galapagos do, but we seldom see reef sharks off the reef, and it's hard to imagine them making the jump from atoll to atoll. They must be able to swim between these different reefs, but we don't know how frequently it happens," he said.

Bowen collected more than 600 tissue samples from surgeonfish, squirrelfish, wrasses, butterfly fish, barnacles, sea cucumbers, corals and more. The tiny samples will be subjected to genetic tests, and the genetic makeup of animals on one island will be compared with those on another.

He worked on the collecting with Kosaki and graduate student Jeff Eble.

Scientists will be able to tell whether there's a lot of genetic interplay between islands, or whether specific reefs seldom share with others and, thus, are somewhat isolated.

Bowen said that while the sharks can swim between atolls as adults, the small reef fish — if they do move readily between islands — would be doing it in their larval form. One of the major issues in discussing the health of reefs and fisheries is whether one part of the Hawaiian archipelago serves as a source of marine life for others.

Reach Jan TenBruggencate at jant@honoluluadvertiser.com or (808) 245-3074.