Ghostnet refers to lost or abandoned fishing gear that drifts in the ocean continuing to catch fish and entangle marine mammals, turtles, and sea birds. The synthetic materials currently used in fishing nets decay extremely slowly, so these nets can continue to drift for years. Many of these 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. During 2001, a multi-agency effort consisting of 3 ships and 18 divers removed nearly 70 tons of debris during 270 ship days at sea. clearing only two atolls in the 1200-mile Hawaiian Archipelago.
Satellite image of an eddy in the Gulf of Alaska.
Given the magnitude of the problem and hazards associated with cleaning the reefs, a multi-agency effort is under way to locate ghostnets in the open ocean and collect them before they reach reefs. (Visit High Seas Ghostnet homepage) The ghostnet team has shown that many of these nets pass through the Sub-Tropical Convergence Zone north of the Hawaiian Islands in the spring of each year when the convergence is particularly strong. Oceanic debris of all types is expected to accumulate here and in other convergence zones. For this reason, searching for ghostnets and other debris in convergence zones was expected to be more efficient than searching the entire ocean.
The Ghostnet team used satellite imagery to locate convergence zones in the North Pacific. An aircraft equipped with a suite of remote sensors was directed to these zones to see if there was, in fact, a higher concentration of debris in these areas. The sensors included an imaging lidar, visible imagers, and an infrared imager. The figure shows an eddy in the Gulf of Alaska that is located in the sea-surface height image from a satellite. This type of eddy indicates convergence of the surface currents. The locations of detections are presented as circles on the flight track across the eddy. It is clear that there are more detections across the eddy than on either side, so this type of search is much more efficient than a random search of the ocean. The next step is to tag nets during an aerial search, so they can be located and retrieved by surface ships.
source: http://www.etl.noaa.gov/programs/marine/ghostnet/ 8mar2006
Thousands of miles from any human habitation, fishing nets lost or abandoned foul huge swaths of the Pacific Ocean. These "ghostnets" continue to fish, untended, entangling and killing fish stocks, marine mammals and birds. While this problem has been known to fisheries managers and fishermen alike, the sheer mass of ghostnets has come as an unpleasant surprise to NOAA scientists. NOAA researchers are developing techniques to identify areas in the open ocean where debris is concentrated and can be cost effectively retrieved.
Because the synthetic materials used in fishing nets decay extremely slowly, lost nets can continue to drift for years. Many 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. Once snagged on reefs they are extremely costly, time-consuming and dangerous to remove.
Catching Ghostnets One strategy to prevent reef damage and protect marine resources is to predict areas of the open ocean where debris is likely to accumulate and can be more efficiently removed. NOAA scientists are using satellite and other technologies to predict areas where currents and winds combine to accumulate debris into convergence zones. Ships can then be efficiently deployed to catch the debris.
A recent field deployment to confirm the accuracy of satellite predictions gave the first substantive look into the severity of the ghostnet problem. According to James Churnside, a researcher with the NOAA Environmental Technology Laboratory in Boulder, Colorado, the bottom line is: "There is a lot more trash out there than I expected."
Using data from several satellites, scientists from the NOAA Satellite and Information Service and the NOAA Fisheries Service tracked the Pacific convergence zone through the winter.
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Figure: William G. Pichel, NOAA Satellite and Information Service
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Researchers used this composite image to identify potential convergence zones and direct flights to map ocean debris. The background shows satellite derived sea surface temperature. Areas where warm and cool colors meet indicate the meeting of warm and cool currents. Blue dots indicate concentrations of chlorophyll. Red lines indicate slicks identified by satellite based radar. The purple line indicates the P3 flight track from Hawaii linking many likely convergence zones. |
In late March and early April, Churnside headed a field survey of areas in the Pacific from a NOAA P-3 Orion Aircraft based in Honolulu. The survey was joint project of NOAA and Airborne Technologies, Inc. of Wasilla, Alaska. Over three days, the plane overflew the convergence zone to allow scientists to make visual observations and to use an electronic imaging system with automated pattern recognition to determine how much and what kinds of debris had accumulated. Churnside said that about 2,000 individual pieces of debris were seen. These included at least 100 that were identified as nets or pieces of net. A number were balls of net up to 10 meters (30 feet) across. "One piece of driftnet that was still stretched out, and presumably still fishing, was 200-300 meters long," Churnside said.
Although surprised by just how much material was found in the convergence zone, Churnside said that analysis will need to be done to determine whether convergence zones are more efficient at trapping debris or whether there simply is much more debris than suspected. "Those are the two possibilities, and we don't have data yet to pick one or the other," he said. Meanwhile, based on the success of the Orion flights, planning is underway to develop a cost-effective removal effort. There are also plans to use unmanned aerial vehicles instead of the larger Orion to identify and track the debris in the convergence zones. A pilot project for at-sea removal could begin as early as next year.
This year, NOAA has also undertaken efforts to re-establish a centralized marine debris capability within the agency. The NOAA Office of Response and Restoration is coordinating these efforts by working with Churnside and other NOAA scientists to bring together, strengthen and increase the visibility of activities related to the prevention, reduction and mitigation of debris in the marine environment. One area of focus will be coordinating activities that identify and reduce the impacts of sea-based sources of marine debris (i.e. fishing nets and derelict gear) on endangered, threatened or protected species, and sensitive habitats in United States waters.
NOAA
Earth System Research Laboratory
Physical Science Division (PSD)
Formerly
Environmental Technology Laboratory
325 Broadway R/ETL
Boulder, Colorado 80305-3328
www.esrl.noaa.gov/psd
source: http://www.etl.noaa.gov/about/highlights/050403/ 8mar2006
To develop tools for locating, assessing and preventing the environmental and navigational impact of marine debris and ghostnets in the Pacific Ocean
Objectives
To identify and prioritize the likely locations of marine debris and ghostnets using remote sensing and oceanographic modelling
To use this information to search oceanic convergence zones for ghostnets and marine debris
To develop debris identification capacity using GPS tracking buoys, LIDAR and other airborne and remote sensors and Geographic Information Systems as the search tools
To create a data and information system and web enabled maps for project implementation
To assess potential risks of marine debris to Alaskan and Hawaiian fisheries, the coastal environment and navigation
To communicate results of the project to stakeholders
Project Overview
In order to search efficiently for marine debri and ghostnets, one needs information on where they are likely to be. This can come from: (1) Historical information (i.e. recent sightings in the past) (2) Chance sightings (i.e. where debris has been sighted by Coast Guard or fishing vessels, research cruises, or aircraft) (3) Knowledge of ocean conditions conducive to collection of marine debris.
Although this project will take advantage of the first two sources of information, we will rely to a great extent on the third source of information since this would form the mainstay of an operational program to recapture hazardous debris in the open ocean.
Using historical and current satellite data, we will identify and locate convergence zones (CV) in the North Pacific since these are likely places for the concentration of marine debris. The same forcing factors that concentrate debris may also concentrate biological productivity and activity. As a result, there may be a significant overlap between the location of the nets and the location of marine organisms at risk of entanglement.
We therefore propose to identify and prioritize the most likely convergence zones. Upon creating our model, we will utilize satellite and airborne remote sensing techniques (LIDAR, gated imaging, thermal and high resolution multi-spectral imagery and synthetic aperture radar technology) to search these high-risk areas to locate and map marine debris. The data gathered will be made available to aid in the removal or destruction of ghostnets. In addition, net spectral signatures will be analyzed and compared with satellite data for continued refinement and possible future satellite detection of these nets.
source: http://www.highseasghost.net/html/about.html 8may2006
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