Marine Debris: Aerial Surveys
For the aerial surveys conducted in the main Hawaiian Islands in February 2006, the survey team consisted of three marine ecosystem specialists trained in marine debris survey techniques, aviation safety, and helicopter emergency egress. Survey flights were conducted with a Hughes 500 helicopter owned and operated by Maui-based Windward Aviation Inc. A January 13, 2006, calibration flight on Maui facilitated the refinement of aerial survey protocols in the following ways:
- Two NOAA observers onboard each flight
- One team member on the ground to follow each flight via computer with a real-time satellite tracking system
- Two flights per day, about 2 h per flight
- Average survey speed: 15-20 kn
- Average distance covered per flight: 48-64 km
- Cruising survey altitude: 335 m (1100 ft)
- Range of distance from shore: 150-400 m (500-1300 ft), depending on reef extension
Surveys were conducted by two observers in a Hughes 500 helicopter. One observer primarily scanned for debris and photographs sites while the other collected spatial data and descriptive data about debris sites. [Click on the image to see in higher resolution].
Each observer onboard the helicopter had a specific set of duties. The aft observer was responsible for scanning the coastline and nearshore waters with a pair of image-stabilizing binoculars and for collecting photographic data on debris sites. The forward observer was tasked with unaided scanning of the coastline, recording descriptive data about debris sites, and obtaining GPS waypoints for specific sites. Descriptive data collected included information on the type, size, and location of the derelict fishing gear (DFG) and on site accessibility.
When DFG was spotted, the observers informed the pilot of its location. If conditions allowed for it, the pilot moved the helicopter closer to the debris site for further observation. The observers and pilot first scanned the surrounding area for humpback whales (Megaptera novaeangliae) and Hawaiian monk seals (Monachus schauinslandi).
If no whales or seals were present, the pilot maneuvered the helicopter down to an altitude of ≥90 m (300 ft) above the site. After observers collected additional data, the helicopter ascended back to an altitude of 335 m (1100 ft) to continue along the survey path.
These aerial surveys revealed the presence of DFG along the shores and nearshore reefs of all islands surveyed in 2006; however, both the number of sites observed and total estimated weights of debris removed were higher at Oʻahu, Kauaʻi, and Lānaʻi than at other the main Hawaiian Islands that were surveyed. . Surveys also revealed that windward-facing shorelines contain substantially more derelict fishing gear than do their leeward counterparts. This observation indicates that northeasterly trade winds play a primary role in debris deposition. Data collected on the types of DFG observed revealed that most debris were trawl nets, a type not used in Hawaiian fisheries.
The aerial surveys of Oʻahu provided an excellent example of the wind-driven nature of DFG deposition. Of 176 debris sites recorded with GPS waypoints during these surveys, 171 of them were located on the windward side of islands.
The Kahuku shoreline contained especially dense accumulations of marine debris and nearly half of the debris sites observed on Oʻahu. The beaches of Waimānalo also exhibited relatively dense accumulations of debris. The five other debris sites were observed near Honolulu International Airport, Kaʻena Point, Barber's Point, Hawaiʻi Kai, and Makapuʻu Point.
The aerial survey of Lānaʻi revealed 122 marine debris sites, all but 2 of which were on windward shores. The region of Shipwreck Beach contained the densest accumulations of DFG found in the main Hawaiian Islands.
Perhaps, because of this island's east-west alignment, perpendicular to the prevailing wind, Molokaʻi proved to have the least amount of DFG on its shores, with only 75 debris sites observed. The heaviest accumulation was recorded on the northwestern shore of Molokaʻi, with other pockets of accumulation along the southwestern coast this island (between Kolo Wharf and Hale o Lono Harbor) and along the eastern shore of this island (near Rock Point).
The rocky cliffs on Maui's windward shores and the geographic orientation of Maui may have been factors that led to the relatively sparse debris settlement observed on this island. The area of highest debris density was the shoreline from Kahului to Honolua Bay. In this stretch, observers found 57 of the 89 debris sites recorded for Maui. In addition, the shoreline south of Hana was found to be an isolated hotspot for marine debris.
The aerial survey of Hawaiʻi revealed 79 debris sites distributed on all sides of this large island. The highest concentration of sites was observed near South Point. Additional marine debris zones included the Waikoloa area southwest of Puakō, the Kawaihae Harbor area, and the region between ʻUpolu 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 DFG. The search covered the leeward waters of this island. Although the whale was not located, the flight allowed for the unexpected documentation of 12 large accumulations of free-floating DFG. 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 Archipelago. Knowledge of the movement patterns of marine debris could allow for concentrated efforts to mitigate the threats of DFG.
Surveys of Kauaʻi also revealed a tradewind-influenced pattern of marine debris accumulation: 150 of the 171 marine debris sites observed at Kauaʻi were recorded in a 50km stretch of this island's eastern coastline. The highest densities of debris were recorded between Kepuhi Point and Nāwiliwili Bay. During these surveys at Kauaʻi, nine monk seal haul-out sites were recorded around this island, some in close proximity to debris accumulations.