A massive oceanic debris gyre has drifted south into Hawaiian waters, driving loads of derelict fishing gear and plastic trash onto Island beaches.

For Hawai'i beachcombers, it means better chances of finding prized glass fishing floats. But for the environment, it's bad news, marine scientists say.

The periodic arrival of the debris-laden gyre — a giant, circular oceanic surface current — poses the threat of entanglement for seals, turtles and seabirds. There is the potential of damage to reefs as huge snags of netting catch coral heads and break them in the surf. And there's the ghost-net problem: lost fishing nets that continue catching and killing fish until the nets are torn to bits or removed from the sea.

Debris drifts regularly with the circulating currents of the North Pacific, but much of it builds up in a quiet region of the ocean associated with a persistent high-pressure zone. When that zone moves south, the debris can get swept out to Hawai'i's shores.

"It's normally between 30 and 40 (degrees latitude) north and 130 to 155 (degrees longitude) west," said Charles Moore, founder of the Algalita Marine Research Foundation and captain of the research vessel Alguita.

The Alguita has made repeated research trips into the North Pacific Gyre, which Moore calls "the Garbage Patch."

The debris field has garnered increasing attention because of its threat to marine life. In March and April 2005, an NOAA aircraft spent three days flying over it with specialized electronic imaging gear provided by Airborne Technologies. More than 2,000 pieces of debris were found, along with more than 100 nets — one of them the length of three football fields, said NOAA Fisheries marine debris specialist Jake Asher, who flew on the mission.

Scientists also have placed tracking devices on drifting nets and found that most appear to drift round and round, until high winds drive them out of the gyre or they run into an island.

And the stuff visible on the surface isn't everything. State Department of Land and Natural Resources naturalist Cynthia Vanderlip, who sailed to the Garbage Patch aboard the Alguita, said that divers have found that the entire water column is filled with debris.

"As the plastic debris fouls with algae, it begins to sink. When you dive down and look up, you see these beams of light and the little bits of plastic look like stars, like looking up into the night sky," Vanderlip said.

Vanderlip has a particular interest in debris, since she watches thousands of pounds of it wash ashore each summer as she works at Kure Atoll, the state wildlife refuge at the northwestern end of the Hawaiian archipelago. Last year, she said, three Hawaiian monk seals became entangled in debris at Kure. She released one that was caught in gill net webbing.

Three blackfooted albatrosses also became entangled in debris on the island, she said.

Moore said that, ultimately, it may be the tiniest pieces of debris that have the biggest effect.

"The amount of plastic in the ocean is going up at a geometric rate. As you sail along, you see a chip, a chip, another chip, a plastic bag, neon tubes, fishing buoys, toothbrushes, hagfish traps, more chips. The pieces break down into smaller pieces, but they don't go away," Moore said. "The most insidious stuff is the stuff that's the same size as the plankton. Fish are eating it.

"There is no such thing as organic fish in the ocean anymore. They're all eating bits of plastic."

Vanderlip said she conducted an experiment in which she caught a salp — a clear, snakelike marine creature — put it in an aquarium and added bits of plastic. The salp readily ate the plastic, and the bits could be seen through the salp's body.

In the wildlife-rich Northwestern Hawaiian Islands, teams collected more than 120 tons of tangles of plastic rope and netting in 2003, and again in 2004. The 2005 results were lower because of the grounding on Pearl and Hermes Atoll of the mother-ship hauling the debris-cleanup crews. The crews were collecting years of accumulated debris, but more debris arrives annually.

"We estimate 40 to 60 tons a year," Asher said.

Moore said that efforts to pick debris off beaches and recent proposals to try to collect big conglomerations of netting at sea won't solve the longer-term problem. Humans have to stop dumping so much plastic into the oceans, he said. One way is to enact stricter controls on the fate of waste products; another may be to develop plastics that break down into nontoxic products.

Vanderlip said that on a recent visit to Kailua beach, she found numerous piles of netting and lines of plastic particles at the debris. Such a sight allows residents and visitors to experience "the beauty of Kailua beach with the world's garbage coming down on it," she said.

Reach Jan TenBruggencate at jant@honoluluadvertiser.com.