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Marine Debris & Entanglement

A Tangled Web: Marine Debris and Hawai‘i’s Marine Mammals

As home to approximately 18 species of whales and dolphins and 1 species of seal, Hawai‘i is a special place for marine mammals. Unfortunately, the islands are also accumulation areas for marine debris from sources across the greater Pacific Ocean. From fishing gear, lost or abandoned at sea, to cigarette butts and bottle caps, marine debris is an increasing problem in coastal areas worldwide. Studies have found that marine debris moves with oceanic currents and atmospheric winds, which together gather debris and deposit it throughout the Hawaiian Islands. Marine debris poses a threat to marine mammals in Hawai‘i primarily through entanglement in derelict fishing gear and through ingestion of debris.  

Plastics
Derelict fishing gear
Plastics
Derelict fishing gear
NOAA
NOAA

Entanglement in marine debris threatens all species of marine mammals found within the Hawaiian archipelago. Throughout the main Hawaiian Islands and the Northwestern Hawaiian Islands (NWHI), derelict or “ghost” nets, are often found as large conglomerations on shorelines, snagged on reefs and drifting in waters offshore. Much of the debris seen fouling reefs and shorelines in Hawai‘i are from fisheries sources in the Pacific - the types of gear used in Hawai‘i-based fisheries are rarely seen. 

Marine mammal entanglements in Hawai‘i have been documented for decades. It is a significant threat to the North Pacific stock of humpback whales which migrate to Hawai‘i each winter. A portion of these animals get entangled in fishing gear (active and derelict) in their feeding grounds in the northern Pacific and carry it with them to Hawai‘i, while others get entangled locally in marine debris. Entanglement in fishing gear and other marine debris may result in drowning, starvation, physical trauma, systemic infections, or increase susceptibility to other threats such as ship strikes. 

Some of these animals free themselves from the entangling gear as indicated by the scars and wounds that the gear has left behind. The documentation and monitoring of these scars has suggested that in some regions of the North Pacific as many as 78% of the humpback whales have been entangled recently. Overall, scientists still do not know how many whales die each year from this threat.  

A program has been established to aid in the disentanglement of these large mammals which can grow to 45 feet long and weigh upwards of 45 tons. The Hawaiian Islands Disentanglement Network (the Network), coordinated by NOAA’s Hawaiian Islands Humpback Whale National Marine Sanctuary, was created in 2002. This Network is part of the larger Pacific Islands Marine Mammal Response Network headed by NOAA’s Pacific Islands Regional Office. These networks operate under the authorization of the Marine Mammal Health and Stranding Response Program (Permit # 932-1489-08) issued by NOAA.

Entangled humpback whale
entangled humpback whale with companion
HIHWNMS, NOAA MMHSRP Permit #932-1489

The Network attempts to free animals with life threatening entanglements. Even so, not every whale can be saved. The Network’s main goal is not to try and cut every whale free, but to garner information on the threat of entanglement so as to aid in its prevention. Disentangling a 45-ton animal is difficult and dangerous for both the animal and the rescue team. Since 2002, multiple humpback whales assessed with threatening entanglements have been successfully disentangled by the Network. Still, much remains to be learned about the mode of entanglement, incidence, and risk to the overall species population. 

Smaller debris items, such as plastic bags and other forms of land-based debris (i.e. litter), also pose a threat to marine mammals. Sometimes marine mammals ingest debris, mistaking it for food.  Similar to entanglements, the ingestion of debris may result in starvation, illness, and death. Unlike entanglements however, ingestion of debris by marine mammals is more difficult to study and monitor and therefore little information exists on the subject. 

The human created problem of marine debris will continue to threaten marine mammals and wildlife worldwide until a solution is found.  Fortunately, we can each do our part everyday to help protect our environment and wildlife from the effects of marine debris.  From recycling and reusing materials, to participating in beach cleanups in your area, working together we can make a difference.

Due to the level of complexity and danger involved no person should ever attempt to disentangle a marine mammal on their own or without proper authorization. You should immediately contact NOAA Fisheries at 1-888-256-9840 or contact the United States Coast Guard on VHF channel 16 (156.8 Mhz).

For more information on marine debris visit NOAA's Marine Debris Program

Marine Debris in Hawai`i
A brochure featuring more detailed informaton about the issue of marine debris in Hawai`i.

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