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New approach to finding marine debris tested

by Barbara McGehan

This summer, guided by satellites and computer models, NOAA Research scientists took to the air to search for marine debris along the Alaska coast. The researchers used a combination of high tech instruments, new techniques, and aircraft, demonstrating for the first time that this coordinated method of searching for marine debris works.

As U.S. coasts become increasingly cluttered with debris from logging, fishing, shipping and dumping, the ability to locate and remove oceanborne debris is growing more important. It’s not just that it’s unsightly to see garbage lying on beaches. Marine debris can also cause serious problems. Lost or abandoned fishing gear that drifts in the ocean (known as ghostnets) can pose a significant hazard. Every year, these nets not only damage coral reefs, but entangle whales, fish, seals, turtles and sea birds. The synthetic materials used in these nets decay at a very slow rate, and so abandoned nets can drift intact for years.

Tons of recovered ocean debris is unloaded at the waterfront; Removal of debris from the open ocean before it becomes entangled on coral is much easier than cutting it away by hand later.

Many of these nets end up trapped on the coral reefs, where entanglement rates are even higher than in the open ocean and where they damage the fragile coral. To remove these nets from reefs, divers must cut the nets off with knives and load them into inflatable boats. It is extremely laborious and dangerous work. Given the magnitude of the problem and the hazards associated with cleaning the reefs, a multiagency effort is under way to locate ghostnets in the open ocean and collect them before they reach the reefs. The problem has been figuring out the best way to locate these nets.

A team from NOAA's Environmental Technology Laboratory (ETL), National Marine Fisheries Service (NMFS), National Environmental Satellite Data Information Services (NESDIS) Airborne Technologies, Inc., (ATI), and other university and industry partners, was assembled this summer under a grant from NASA to the State of Alaska. Using a small, highly instrumented aircraft, scientists surveyed an area along the Pacific Coast from Oregon to Alaska to test whether this new method of searching for marine debris was effective.

“Ocean circulation models were run to identify regions and periods of convergence, where debris would be likely to concentrate. These areas were examined using space-based instruments to locate actual convergence zones more precisely,” said James Churnside, the lead scientist from NOAA’s Environmental Technology Laboratory in Boulder, Colo.

The aircraft was equipped with an instrument package developed by ATI and NOAA/ETL for ocean survey work. The suite of sensors, including visible and thermal imagers, a fish/lidar/gated imager developed at NOAA/ETL, sea surface temperature radiometer and ocean color radiometer, were linked by a software package to detect objects floating at the surface and sub-surface of the water.

The model, developed by NOAA Fisheries, identified several locations along the coast of Alaska and along the Alaskan continental shelf where eddies and convergences are common. The satellite data located a number of specific areas, both near the shore and farther off shore, where debris was expected to collect.

“The Alaskan survey was used because the problem of ocean debris is very real for remote Alaskan native communities,” said Tim Veenstra, president of Airborne Technologies, Inc. “For instance, the beach at St. Paul in the Pribilof Islands is constantly littered by this debris. Also, ghostnets may adversely affect Bristol Bay and Yukon River salmon runs.”

Bill Hogarth, assistant administrator for NOAA Fisheries said, “This experiment clearly demonstrated that we can use models and satellites to direct aircraft to anticipated areas of debris - allowing a much more focused search and effective removal of the debris.”

In the future, the researchers hope to survey the North Pacific Convergence Zone, an area north of the Hawaiian Islands. “Most of the coral reefs in the U.S. lie in the waters around Hawaii. If we can spot debris, especially the “ghostnets” , that drift in the ocean, we can remove them before they damage the reefs.” said Churnside.

[10/6/03]

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