By Nina Wu
It's confirmed. Most of the marine debris landing on Hawaii's shores is made up of — plastics. Very small plastics.
An aerial survey by the Department of Land and Natural Resources and North Pacific Marine Science Organization of all coastlines in the eight main Hawaiian islands shows that plastics constitute most of the marine debris landing on our shores.
The sparsely populated island of Niihau had the highest concentration of debris, at 38 percent, compared to Oahu, which had the lowest, at 5 percent.
A very limited amount of debris was associated with the Japan tsumani, according to DLNR chair Suzanne Case. The study was funded by the Ministry of the Environment of Japan as part of the Japan Tsunami Gift Fund.
Multiple photos were captured every 0.7 seconds from a Cessna 206 about 2,000 feet above ground.
"Most of what was mapped is common, everyday items that someone haphazardly tossed onto the ground or directly into the water," said Case. "These items get caught up in ocean currents and unfortunately much of it eventually lands, mostly on north and east facing shores. Hawaii is recognized around the world for our beautiful beaches. Unfortunately we cannot say they are pristine, because they've been so seriously impacted by our trash."
The following is a synopsis of the full report which used imagery analysis for the aerial survey conducted between August and November 2015. (from highest to lowest):
Niihau — Identified a total of 7,871 pieces of marine debris. Most of it was plastic (46 percent), followed by buoys and floats (35 percent). The greatest density of debris were found on east-facing shores.
Molokai — Identified a total of 2,878 piece of marine debris, 37 percent plastic, 35 percent buoys and floats. Concentrated on the northwestern shores and a small area on the northeastern corner of the Friendly Isle.
Hawaii — Identified a total of 2,200 pieces of marine debris, 52 percent plastic. Concentrated on the southeastern tip of the island around Kamilo Point.
Kauai — Identified a total of 1,849 pieces of marine debris, 49 percent plastic, concentrated on the eastern shores.
Lanai — Identified a total of 1,829 piece of marine debris, 53 percent plastic, concentrated on the northeast coast.
Maui — Identified a total of 1,749 pieces of marine debris, 40 percent plastic, concentrated on the northern side around Kahului.
Kahoolawe — Identified a total of 1,298 pieces of marine debris, 47 percent plastic, concentrated on the northern tip of the island and the Keoneuli area on the eastern coast.
Oahu — Identified a total of 984 pieces of marine debris, 63 percent plastic, concentrated on the northern tip around Kahuku.
On March 11, 2011, the Tohoku Earthquake and resulting tsunami devastated Japan, creating millions of tons of debris that got swept into the ocean. The first confirmed tsunami-related debris that landed on Hawaii's shores was a blue plastic, fishing container on Sept. 18, 2012 off Makapuu. Since then, 21 vessels and an assortment of buoys, fishing containers, signs and other items have been recovered in Hawaii.
Wildlife become entangled in nets and lines, or mistakenly eat pieces of plastic and foam, confusing them for food. The report (p. 41) includes photos of endangered monk seals on Niihau resting on beaches littered with marine debris, including plastic and derelict fishing gear.
The debris was classified into seven categories, including buoys and floats, foam, derelict fishing gear, plastic, tires, other (includes processed wood, metal, cloth, abandoned boats) and inconclusive. Below, some plastic debris and a tire.
The most common type of debris found on all islands was plastic, making up 47 percent of the overall composition of debris identified, and at least 37 percent of the debris on any individual island.
On Oahu, Hawaii's most populous island, marine debris was concentrated on the northern tip of the island, on the east-facing shore between the northernmost point and Kahuku area. But a whopping 63 percent was identified as plastic. It's possible that the lower concentration of marine debris on Oahu reflects continuous beach clean-up efforts by local residents and conservation organizations, according to former DLNR Marine Debris Coordinator Kirsten Moy.
So what are the next steps? To use the data to organize and plan cleanup efforts, as well as to develop a community-accessible database to distribute the debris data and track removal efforts throughout the isles.
Related video featuring Kirsten Moy, DLNR's former Marine Debris Coordinator (courtesy DLNR):