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Pacific Southwest, Region 9

Serving: Arizona, California, Hawaii, Nevada, Pacific Islands, Tribal Nations

Marine Debris in the North Pacific:
Frequent Questions

Marine debris can degrade ocean habitats, endanger marine and coastal wildlife, interfere with navigation, result in economic losses, and threaten human health and safety. Beginning in the 1970s a growing number of studies on the occurrence and effects of marine debris in the open ocean have provided a greater, yet still incomplete, understanding of this vast problem. This report answers some frequently asked questions about the scope of marine debris in the North Pacific Gyre and its potential impacts; however, research is not yet complete on this issue, so this report also identifies data gaps that highlight some of the questions remaining to be answered.

Frequent Questions

(Click a question to open/close its answer.)
What is marine debris and where does it come from?

Marine debris is any solid, manufactured material that is disposed of or abandoned into the marine environment. It may consist of plastic, glass, metals, polystyrene, rubber, derelict fishing gear and derelict vessels. Plastics are estimated to represent between 60% and 80% of the total marine debris floating in the world’s oceans. Almost all of the plastic debris in the North Pacific consists of very small pieces of plastic floating at or slightly below the water surface. Such debris is composed of fragments of manufactured plastic products (user plastic) and also preproduction plastic pellets that were spilled at some point during shipping or at the factory.

Debris is generated on land at marinas, ports, rivers, harbors, docks, and storm drains. Debris is generated at sea from fishing vessels, stationary platforms and cargo ships. In the Northwestern Hawaiian Islands – Marine National Monument (NWHI-MNM), approximately 52 metric tons of derelict fishing gear accumulate annually. Once it is in the ocean, it is very difficult to pinpoint the exact source of most of this debris.

Click on the below links to additional data sources and information about preproduction plastic pellets:

Data Gap

In order to gain an accurate and meaningful assessment of the quantity and type of plastics and their influence, large-scale and long-term monitoring is needed across countries and environments, including the sea floor, and across a range of debris sizes, from very small micro-debris to large debris items such as derelict fishing nets.

How do wind and ocean currents affect the concentration of plastics and other marine debris?

Multiple atmospheric and oceanic currents flow in a general clockwise pattern around the North Pacific to create what is known as the Pacific Gyre. When derelict nets and other marine debris circulating in the open ocean enter the Pacific Gyre they usually remain there. This has created an ongoing concentration of debris. Scientific models suggest marine debris deposited along the coast tends to accumulate in the central oceanic gyres within two years after deposition. This area of concentrated debris consists of two accumulations: the "Western Garbage Patch" located off Japan and the "Eastern Garbage Patch" located between Hawaii and California. These two sub-gyres are connected by a narrower band of marine debris north of the Hawaiian archipelago referred to as the Subtropical Convergence Zone (STCZ). The STCZ migrates north and south with seasonal changes in air and sea surface temperatures and fluctuations on ocean currents. (Figure 1).

Figure 1. Generalized Illustration of STCZ and Garbage Patch Locations
Figure 1. Generalized Illustration of STCZ and Garbage Patch Locations
Data Gap

The occurrence and transport mechanisms of marine debris in the surface waters and coastal habitats of the North Pacific are well documented. Unfortunately, due to the logistics of sampling the substrate in deep waters, the occurrence of marine debris on the seafloor is less known. Accumulation of micro-organisms and algae onto plastic debris in surface waters may alter the buoyancy of the plastic, resulting in sinking and deposition on the seafloor.

How much marine debris ends up in the Pacific Gyre?

The distribution and quantity of marine debris within the garbage patches are difficult to determine because they are constantly expanding and moving. The patches are estimated to contain approximately 100 million tons of garbage; most of the debris is found just below the water surface, extending down to depths of 100 feet or more, and is not tightly packed. Approximately half of all plastics are neutrally to positively buoyant and thus remain close to the ocean surface. Over time as the plastic breaks down into smaller pieces, organism and sediment fouling add weight to the particles which can cause the plastics to sink and eventually reach the seabed.

Limited research indicates that most land-based marine debris originates in the Western Pacific. The California Coastal Commission found that plastic bags comprise 13.5% of shoreline litter; the City of Los Angeles found that plastic bags made up 25% of litter in storm drains. Data from the California Department of Transportation (Caltrans) found that polystyrene makes up 15% of storm drain debris. The most commonly found items on beaches in Orange County, California are plastic pellets (17% by weight), expanded polystyrene, and other plastic food and beverage containers. In the Papahānaumokuākea Marine National Monument of the Northwestern Hawaiian Islands, approximately 52 metric tons of derelict fishing gear accumulates annually. 96% of the plastic found in the North Pacific was small pieces of plastic, more than in any other ocean.

For more information, visit the Papahānaumokuākea Marine National Monument.

The highest densities (number per square kilometer) and concentrations (gram per square kilometer) of plastic floating at or just below the surface occurred in the Japan Sea/nearshore Japan Water, in Transitional Water, and in Subtropical Water. Studies based on satellite-derived information and ocean circulation models, and confirmed by flight observations, show that the largest debris concentration in the North Pacific is found within the North Pacific STCZ. Debris densities appear to be significantly correlated with sea-surface temperature and chlorophyll-a concentration.

Data Gaps

Few studies have attempted to quantify the abundance and mass of floating debris in the open ocean, perhaps because ship time for extensive open ocean trawls are costly and time-consuming. Analyses of plastic debris in the environment derived from beach-cleaning surveys typically only provide data on coarse trends and larger items More studies are needed to correlate marine debris accumulations with currents and shipping lanes to determine the fate and transport of debris––sources and destinations––to target clean up and prevention efforts.

How do plastics and other marine debris negatively affect the environment?

Marine debris travels throughout the world’s oceans, accumulating on beaches and within gyres. This debris can degrade physical habitats, transport chemical pollutants, threaten marine life, and interfere with human uses of marine and coastal environments. Plastic marine debris has great potential to alter the environment and impact humans and wildlife since it floats at the surface, is widely transported by ocean currents, persists in the environment for years, and is not readily digestible when consumed. Therefore, the impact of plastic marine debris is much more than a mere aesthetic problem.

Physical Habitat Impacts

As debris accumulates, habitat structure may be destroyed, light levels may be reduced in underlying waters, and oxygen levels may be depleted. These changes can undermine the ability of marine life to survive in open water and on the ocean floor.

Derelict fishing gear, including nets and lines, can settle on coral reefs as currents and waves transport them to shallow habitats, resulting in fragmentation and abrasion of coral branches. Degradation of coral reefs globally has the potential to undermine the survival of a diverse array of invertebrates, fish, and vertebrates that depend on this limited resource, including a number of threatened and endangered species.

Chemical Impacts

Persistent organic pollutants (POPs) are chemical compounds created in manufacturing and other human activities that persist for a long time in the environment. Marine debris, specifically plastics, is itself a mechanism for the transport of POPs. Plastics may contain other organic pollutants such as phthalates, organotins, and phenols, including bisphenol A (BPA). Plastics also attract and concentrate PCBs, polycyclic aromatic hydrocarbons (PAHs), and DDT and other pesticides and can serve as a potential global transport mechanism for contaminants.

How are seabirds, turtles, fish and other animals harmed by plastics and other marine debris?

There is a substantial body of evidence documenting the negative effects of marine plastic debris on marine biota. It has been estimated that plastic marine debris adversely affects 267 species globally, including 86% of sea turtles, 44% of seabirds, and 43% of marine mammals. The most common threats include ingestion and entanglement.

Ingestion of plastic debris by seabirds, fish, and sea turtles has been widely documented, and incidences of ingestion have been reported for marine mammals as well. Additionally, fur seals and other predators may indirectly consume plastics by eating fish and other prey that have already ingested plastic debris. The plastics can block an animal's digestive system, ultimately causing death.

Marine debris entanglements have been documented for 135 species of invertebrates, fish, seabirds, sea turtles, seals, sea lions, dolphins, and whales, with many species experiencing injury and even mortality. One of the greatest threats of entanglement to marine life and seabirds is derelict fishing gear, including monofilament line, trawl nets, and gill nets. Lost and free floating fishing gear can continue to "ghost fish" for months and even years, ensnaring a wide range of species, particularly in areas adjacent to fishing grounds, along current convergence zones, and along shorelines where debris is deposited by currents and waves.

How are humans affected by plastics and other marine debris?

In addition to degrading the habitats and ecosystem services that humans use, plastic marine debris can directly interfere with navigation, impede commercial and recreational fishing, threaten health and safety, and reduce tourism. Large debris, such as derelict fishing nets and lines that float at or just below the surface, pose the greatest threat to vessel navigation. Lines and nets can become wrapped around propellers and entrained in intakes of motors, and vessels may strike large items, damaging hulls and propellers. Immobilization of commercial and recreational vessels can result in increased cost of navigation due to lost time, costly repairs, as well as the loss of human life. In a tragic example, derelict fishing gear contributed to the sinking of a Korean passenger ferry in 1993 that resulted in the deaths of 292 passengers.

Humans can also be directly impacted by marine debris, becoming entangled in nets and lines while swimming or being injured by sharp debris that accumulates on beaches. It is not uncommon for scuba divers to become entangled in nets or lines. In most instances they are able to free themselves; however, in rare instances entanglement has resulted in injury and even death.

Not only does the accumulation of debris pose a human health risk, but it also reduces the aesthetic and recreational values of beaches and marine resources. The buildup of plastic debris on beaches is of particular concern for coastal cities, since unsightly debris, and the distressing sight of entangled marine life and seabirds, can reduce the area’s attractiveness to local residents and tourists. As a result, immense economic costs are incurred to clean marine debris from beaches.

Data Gap

The effects of small-plastic debris on marine animals, including toxicity of pellets and fragments that wash up on beaches throughout the Hawaiian Archipelago, remains unknown but should be investigated.

Further data is also needed to assess the transfer of pollutants found in and accumulating on plastic to marine life and potentially throughout the marine food web. Impacts to humans from consumption of fish and invertebrates that ingest plastics are in large part unknown. Currently, there is only a limited amount of data on the transfer of POPs from plastic marine debris to conspicuous marine organisms, such as sea birds. By studying the effects of plastics on everything from plankton to top predators, a better understanding of potentially important impacts of plastics throughout the food web can be gained.

Download the full report with references in PDF format:
Marine Debris in the North Pacific - Existing Info + Data Gaps (PDF) January 2011 (23 pp, 700K)

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