The aerial survey team consisted of three marine ecosystem specialists trained in marine debris survey techniques, aviation safety, and helicopter emergency egress. Survey flights were conducted using a Hughes 500 helicopter owned and operated by Maui-based Windward Aviation Inc. A January 13 calibration flight on Maui facilitated the refinement of aerial survey protocols as follows:
- Two NOAA observers onboard each flight
- A team member on ground follows the flight via computer with a real-time satellite tracking system
- Two flights per day, about 2 hours per flight
- Average survey speed: 15-20 knots
- Average distance covered per flight: 30-40 miles
- Cruising survey altitude: 1100 feet
- Range of distance from shore: 500-1300 ft (400 meters), depending on reef extension
Each observer onboard the helicopter has a specific set of duties. The aft observer is responsible for scanning the coastline and near-shore waters with a pair of image-stabilizing binoculars, in addition to collecting photographic data on debris sites. The forward observer is tasked with unaided scanning of the coastline, recording descriptive data about debris sites, and obtaining GPS waypoints for specific sites. Descriptive data collected include information on the type, size, and location of the derelict fishing gear in addition to site accessibility.
When derelict fishing gear is spotted, the observers inform the pilot of its location. If conditions allow, the pilot moves the helicopter closer to the debris site for further observation. The observers and pilot first scan the surrounding area for humpback whales and Hawaiian monk seals. If no whales or seals are present, the pilot maneuvers the helicopter down to an altitude of not less than 300 feet above the site. After observers collect further data, the helicopter ascends back to an altitude of 1100 feet to continue along the survey path.
The aerial surveys revealed the presence of derelict fishing gear along the shores and nearshore reefs of all islands surveyed; however, Oahu, Kauai, and Lanai significantly surpassed the others in both the number of sites observed and total estimated weight of debris. Surveys also reveal that windward-facing shorelines contain substantially more derelict fishing gear than their leeward counterparts. This observation indicates that northeasterly trade winds play a primary role in debris deposition. Data collected on the types of derelict fishing gear observed revealed that most were trawl nets, a type not used in Hawaiian fisheries.
Individual Island Observations
The aerial surveys of Oahu provided an excellent example of the wind-driven nature of derelict fishing gear deposition. Of 176 total GPS debris sites recorded from the helicopter surveys, 171 of them were on the island's windward side.
The Kahuku shoreline contained especially dense accumulations of marine debris, grossing nearly half of the sites observed on Oahu. The beaches of Waimanalo also exhibited relatively dense accumulations of debris. The five other nets were observed near the airport, Kaena Point, Barber's Point, Hawaii Kai, and near Makapu'u Point.
The survey of Lanai revealed 122 marine debris sites, all but two of which were on windward shores. The region of Shipwreck Beach contains the densest accumulations of derelict fishing gear in the main Hawaiian Islands.
Perhaps due to the island's east-west alignment, perpendicular to the prevailing wind, Molokai proved to have the least amount of derelict fishing gear on its shores, with only 75 individual debris sites observed. The heaviest accumulation was observed on Molokai's northwestern shore, with other pockets of accumulation along the southwestern part of the island (between Kolo Wharf and Hale O Lono Harbor) and along the eastern part of the island (near Rock Point).
The rocky cliffs on Maui's windward shores and the geographic orientation of Maui may be factors leading to relatively sparse debris settlement on the island. The area of highest debris density was the shoreline ranging from Kahului to Honolua Bay. In this stretch, 57 of Maui's 89 debris sites were recorded. In addition, the shoreline south of Hana was found to be an isolated hotspot for marine debris.
The aerial survey of the Big Island revealed 79 specific debris sites distributed on all sides of the island. The highest concentration of sites was observed near South Point. Additional marine debris zones included the Waikoloa area southwest of Puako, the Kawaihae Harbor area, and the region between Upolu Point and Waimea Valley.
On February 17, 2006, the aerial survey team set out from Kona Airport in an unanticipated search effort to locate a whale that was reported by the Hawaiian Islands Humpback Whale National Marine Sanctuary to be entangled in derelict fishing gear. The search covered the Big Island's leeward waters. Although the whale was not located, the flight allowed for the unexpected documentation of 12 large accumulations of free-floating derelict fishing gear. In the future, the Marine Debris Team hopes to attach tracking buoys to such floating debris accumulations to provide more information on the paths of free-floating marine debris in the Hawaiian Islands. Knowledge of the movement patterns of marine debris could allow for specially concentrated efforts to mitigate the threats of derelict fishing gear.
Surveys of Kauai also revealed a tradewind-influenced pattern of marine debris accumulation, as 150 of the Kauai's 171 marine debris waypoints were recorded in the 50 kilometers of Kauai's eastern coastline. The highest densities of debris were recorded between Kepuhi Point and Nawiliwili Bay. During the surveys, nine monk seal haul-out sites were recorded around the island, some in close proximity to debris accumulations.