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Expedition using
lasers to study fish

If predators flee the device, a
possible shark-repelling laser
could be created

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By Helen Altonn
Star-Bulletin

Two vessels investigating ecological resources in the Northwestern Hawaiian Islands are beginning explorations this week at Kure Atoll, the northernmost atoll in the chain.

The chartered Certified Marine Expedition vessel Rapture and the National Oceanic and Atmospheric Administration ship Townsend Cromwell were to rendezvous at Midway over the weekend to work together and exchange some personnel and equipment.

Aquatic biologist Bill Walsh on the Rapture wants to retrieve a specially created underwater laser light that the manufacturer sent by mistake to the Cromwell.

Walsh and his team have been experimenting with less-powerful laser lights to study underwater animals. They're like hand-held laser pointers used in boardrooms but they're waterproof and emit green light instead of red.

The lasers allow the divers to measure fish accurately, Walsh said.

Since red-colored light beams can travel only a few feet, Walsh and his team began looking into use of a green laser that can transmit light farther underwater. They found a mainland company had started developing one.

They obtained some about eight months ago and began testing them off Kona on the Big Island to prepare for the Northwestern Hawaiian Islands expedition.

Although the devices worked well, Walsh asked the company to develop a more powerful version to reach 30 feet or more "for use in big predator country." That was the laser that went to the Cromwell.

The scientists noticed that fish have different reactions to the light. Some think the beams are prey and chase the light.

They said the lasers may help to determine the feeding territory of certain fish, like hawkfish, that feed only in limited areas around their coral homes.

If the lasers cause large fish like sharks to flee, the researchers suggested, perhaps a laser "shark billy" could be created to make divers feel more secure under water.

Aquatic biologists reported unexpected encounters with large reef fish that rattle a few theories of fish behavior in the main islands.

"Everywhere we go, we are swarmed by large schools of nenue," said Steve Cotton, working with the University of Hawaii-Hilo and state Department of Land and Natural Resources.

He said nenue surrounded the divers at Nihoa and Necker Islands and at French Frigate Shoals, and other fish exhibited similar behavior.

In the main Hawaiian islands, such swarming behavior has been attributed to fish feeding by tourists.

Rather than a solely learned response, however, Cotton said the swarming behavior at Nihoa and other sites appeared to be "a natural response to a stimulus in the water that's enhanced by fish feeding."

The giant ulua also exhibited such behavior, which can be troublesome for divers trying to count fish, said fisheries specialist Brent Carman. At times they were surrounded by 30 to 50 ulua.