The Joint Group of Experts on the Scientific Aspects of Marine Environmental Protection (GESAMP) has recently published a new report on sea-based sources of marine litter (2021 #108), which provides an overview of the sources and negative effects of marine litter, in particular plastic litter. The report assesses the current availability of data and stresses the urgent need to reduce marine litter. It outlines a number of ongoing initiatives and suggested steps to combat this issue. It also highlights knowledge gaps and suggested areas for future academic and scientific research and provides readers with practical information.

I. Research background

Marine litter is defined as “any persistent, manufactured or processed solid material discarded, disposed of or abandoned in the marine and coastal environment as a result of human activity”. It has been recognized as a threat to ocean health since our understanding of the environment aspects of human actions in the world’s ocean started to expand in the 1970s. The concern is compounded by the quantity of plastic that has been manufactured, used and discarded globally since its commercial advent in the 1950s. In the last decade, there has been growing knowledge on the levels, sources, negative impacts of marine litter and microplastics in ocean, as well as measures to reduce their harm. However, levels of marine litter and plastic waste are continuing to increase, together with their impacts on biodiversity, ecosystems, fisheries, animal welfare, maritime transport and safety at sea.

Following an agreement in principle at the 45^th annual session of GESAMP in 2018, the Working Group on sea-based sources of marine litter (WG 43) was established formally in April 2019. The overall objective of WG 43 is to build a broader understanding of sea-based sources of marine litter, in particular from the shipping and fishing sectors, including the relative contribution of different sources, analysis of plastic use and management within both industries and the range and extent of impacts from sea-based sources of marine litter, and finally to guide interventions on these identified priorities, drawing upon the expertise of relevant organizations.

II. Sources of marine litter

It is generally assumed that the majority of plastic waste entering ocean comes from land-based sources (some claiming a contribution up to 80%). However, marine litter also results from sea-based activities. Further, some forms of sea-based marine litter may not only be significant sources of plastic litter, but may well have greater impacts on marine biota and habitats than other forms of marine litter do. The report puts its focus on primarily five sources of marine litter as follows.

1. Fishing

According to FAO statistics, the global fishing fleet in 2018 was estimated to include 4.566 million vessels. Global fish production reached a peak of 179 million tonnes, with 54% from capture fisheries and 46% from aquaculture. Approximately 87% of total production was for human consumption. A major component of sea-based marine litter is abandoned, lost or otherwise discarded fishing gear (ALDFG) from artisanal, commercial and recreational fishing operations, including gear components and metallic materials such as netting, ropes and lines, floats and buoys, sinkers and anchors. As a result of extreme weather events, normal wear tear, bite-offs from wildlife, or existence of underwater obstructions, gear can be lost on an occasional or regular basis. A study in 2019 estimated that 5.7% of all fishing nets, 8.6% of all traps and 29% of all lines are lost to the world’s ocean annually. ALDFG in the sea may lead to reduced viability of certain marine species, morbidity and mortality of marine wildlife, damage to marine habitats, social impacts on coastal communities, and even loss of human life.

2. Aquaculture

With an increasing sociocultural demand for seafood, global aquaculture production has risen steadily over the years. As of 2016, 202 nations were engaged aquaculture and nearly 600 aquatic species were cultured for human consumption (FAO 2018). Marine aquaculture systems generally incorporate ropes, buoys, mesh bags and anti-predator netting. It is often assumed that aquaculture operations produce marine litter primarily through normal wear and tear of plastic gear, accidents that damage equipment, catastrophic losses during extreme weather events and improper waste management by aquaculture operators. Unfortunately, no global estimates exist for the amount of plastic waste generated by aquaculture operations at regional or national levels. Only an assessment was made on aquacultural operations in the European Economic Area (EEA) where aquaculture-associated gear and debris losses are grossly estimated to range from 3,000 to 41,000 tonnes annually, and aquaculture debris already present in the EEA’s marine environment may range from 95,000 to 655,000 tonnes.

3. Shipping and boating

International maritime trade is closely tied to the development of the global economy. For the years between 1970 and 2017, global maritime trade increased an average of 20%. For the first half of 2020, approximately 53,000 merchant ships were registered by IMO globally. Expansion in merchant shipping has led to more congested shipping lanes, which increases the risk of environmental impacts to the ocean from normal shipping and accidental events. Plastic debris generated from end-of-life vessels, including fibre, solid foam and PVC, and microplastics in grey water and ballasts are largely responsible for the marine plastic litter in the sea attributable to shipping.

Although the discharge of garbage from ships is regulated by MARPOL and other national environmental regulations, plastic wastes are most often disposed of accidentally. Few detailed studies are available that quantify the amounts and types of plastic litter from shipping, but a recent survey provides that cargo residues each year account for 0.001%-2% of cargo load, and an average of 0.01-0.1m³ of operational wastes and 0.003-0.015m³ of plastic and domestic wastes are generated per person per day. Discharge of these waste into the ocean can bring detrimental consequences and offending vessels and individuals will certainly be penalised. The price paid can be high as one estimate placed the total value of litter damage to shipping in the APEC region at USD 279 million per year.

4. Dumping of waste and other matter at sea

Of all the wastes that may be disposed of at sea, by far the highest volumes and tonnages reported as being dumped around the world are dredged materials. Although over the past several decades, laws and regulations have been compiled by many countries under the auspices of LC/LP, information on the quantities of plastics or other litter contained in those wastes remains extremely limited. Due to the lack of routine monitoring, those dumped wastes including dredged materials contain significant amounts marine litter and microplastics but are difficult to be estimated with quantitative data.

5. Other ocean uses

Due to the limited availability of information, quantifying litter and microplastics from other sources is a challenge, but there is evidence that the use of microplastics in offshore oil and gas activities could be substantial. Most estimates are likely underreporting the actual level of plastic discharge. About 65-70% of weather balloons released on land by meteorological services end up in the ocean and eventually contribute to marine debris. The frequent loss of shark nets along the coast is also a major contributor. Artificial reefs that have plastic (especially polyvinyl chloride) or rubber components are at risk of degradation, leaching of toxic chemicals into the surrounding environment, break up into microplastics, and dispersal. Spacecrafts and single-use plastics used in scientific research are not documented nor reported by national research programs for the quantity and frequency.

III. Solutions for reducing marine litter

Given the diversity of marine litter sources, it is clear that efforts to reduce marine litter demand research into causes, quantities, impacts and solutions for sea-based sources of marine litter to generate the evidence necessary to inform management and policy change recommendations at all scales.

A wide array of actions and approaches will also be required. These will include, first, a combination of fisheries management and regulatory measures, modifications and innovations in gear design and operation, and increased availability of port reception facilities to prevent abandonment and discarding of end-of-life gear.

A standardised approach to waste management by the global shipping sector is necessary for data elucidating quantity, category, time and location of disposed litter and for improved availability and use of PRFs.

Finally, efforts to reduce sea-based sources of marine litter will require targeted and effective education and awareness-raising among stakeholders across all sectors – government, industry, academia, NGOs and communities – in order to build consensus and will for effecting change.

For more information, please contact Managers of the Association.