We know that bottom trawling harms the marine environment, small-scale fishers and the climate. But in what way and how do its impacts vary between different parts of the world? And what can we do to limit its harm? The Transform Bottom Trawling Coalition is here to answer all of your questions
Bottom trawling is a fishing method that involves dragging a net along the seafloor to catch fish and other marine life. The net is typically held open by heavy steel bars called beams or by two wooden or metal wings called doors. It is classified as a mobile fishing gear, meaning the nets must move to catch fish.
Bottom trawling is often described as “non-selective” because fishers cannot control what enters the net. As a result, bottom trawlers tend to indiscriminately catch large volumes and diversities of unwanted marine species, and can disturb or destroy sensitive seabed habitats in the process.
Although local impacts of bottom trawling have long been recognised, it became a global concern in the mid-20th century. The advent of steam power and modern industrial fishing technologies allowed vessels to travel farther, stay at sea longer, and fish with much greater intensity. Today, bottom trawlers operate in nearly every coastal country and account for more than a quarter of the world’s wild-caught seafood.
Dredging is a similar fishing method to bottom trawling, but instead of using a net, dredgers tow heavy chain bags attached to metal rakes across the seabed. These rakes dig into the seabed to extract animals living in the sediment, such as scallops and wild oysters.
Because dredging disturbs the seabed and marine life in comparable ways, we often include dredging when we talk about bottom trawling.
Although less widespread globally, dredging can cause particularly severe local damage due to the depth to which the teeth on dredging gear penetrate the seabed.
Bottom trawling is the single most widespread source of human-driven disturbance to the world’s seabed habitats. Most bottom trawling happens close to shore, where small-scale fishing activity, marine biodiversity and seabed carbon is concentrated. The vast majority of bottom trawling occurs within 200 nautical miles of our coasts, and bottom trawling intensity is twice as high within 12 nautical miles from the shoreline. This is problematic because coastal waters are home to artisanal and small-scale fishers, so intensive bottom trawling in these areas increases the likelihood of competition and conflict.
Shallow coastal waters are also where most marine life lives, hence why they are trawled so intensively. Highly sensitive ecosystems like seagrasses and various types of living reefs can only exist in shallow coastal waters, so they are particularly vulnerable to bottom trawling.
Many of the world’s major bottom-trawling regions overlap with areas where small-scale fishing is most prevalent. Today, Asia and Africa account for the largest bottom-trawl catches globally.
The areas with the highest intensity of bottom trawling have shifted over the past century. Bottom trawling intensity was highest in European waters for most of the 19th and 20th centuries, but the practice expanded rapidly in Asian and African countries from 1950 onwards.
The world’s bottom trawling fleet comprised around 55,000 vessels in 1950. Most of these worked in the Mediterranean and North Sea and they impacted about 5 million km2 of the seabed. By 2010, the number of vessels almost tripled. At the same time, the area of the seabed impacted by trawling rose to 14 times the footprint in 1950. These figures illustrate the exponential growth in bottom trawling intensity in recent decades, reflecting the rapid industrialisation in the world’s bottom trawling fleets.
Asia is the world’s bottom trawling hotspot today, but fleets are growing rapidly in Africa and continue to be significant in Europe. In Africa, around half of bottom trawling activity is driven by vessels flagged to Asian or European countries. The high intensity of bottom trawling in the coastal waters of Asian and African countries poses a significant risk to small-scale fisheries.
Bottom trawling is a fishing method with significant environmental consequences. It is the only technique conclusively linked to all three major impacts of fishing on marine life:
We don’t know the full extent of bottom trawling’s impacts on marine life. Bottom trawling is so widespread and its impacts on marine life are so far-reaching that it is very difficult to properly assess how it is altering our marine environment.
Bycatch and discards have long been a challenge in bottom trawl fisheries because of the method’s non-selective nature. Species caught unintentionally by bottom trawlers are called bycatch. Bycatch that is returned to the sea, often dead or dying, is referred to as discards.
Bottom trawling’s bycatch problem is a global issue. Globally, bottom trawling is consistently associated with high bycatch rates, with bycatch accounting for between 60% and 95% of overall catch in many studied fisheries. Bycatch mostly involves fish and invertebrates that live near the seabed, but it can also affect other species, such as seabirds. Seabirds are amongst the most threatened species groups in the world and trawl-related mortalities can severely hamper their recovery.
Some bottom trawling bycatch is used for bait or sold as low-quality fish, but most is thrown overboard. Some hardy animals discarded by bottom trawlers may survive, but most do not, and it is very difficult to know or record their fate. They are typically either crushed in the net while it is towed behind a boat, die from the rapid change in barometric pressure when the net is brought to the surface, or suffocate as catch is sorted on deck. Fish that manage to escape trawl nets underwater often die due to injuries and stress, with these deaths generally unaccounted for in discard statistics.
Like soil on land, healthy seabeds are the foundation of life in our oceans. They host complex ecosystems like coral reefs, sponge gardens and seagrass meadows that provide habitats, shelters and breeding grounds for a staggering diversity of species.
In the short term, bottom trawling can change the seabed’s shape and texture by removing communities of structure-forming animals like sponges, corals, oysters and worm colonies. These species create habitats that other species need to grow and survive. As the availability of complex seabed habitats is reduced, the number and diversity of animals living in marine sediments decreases.
Over the long term, bottom trawling can fundamentally alter the balance and composition of entire ecosystems. However, the severity and extent of its impacts on the seabed vary significantly based on three main factors: seabed penetration depth, trawling intensity, and the type of habitat being trawled.
Like nearly all fishing activities, bottom trawling contributes to the climate crisis through direct fuel emissions. Bottom trawlers are particularly fuel intensive because towing heavy gear along the seabed requires more energy than most other fishing methods.
Beyond fuel use, bottom trawling has a unique and significant impact: it disturbs carbon-rich sediments on the seafloor, which are among the planet’s largest natural carbon sinks. When these sediments are disrupted, stored carbon is released into the water and potentially the atmosphere, adding to greenhouse gas emissions.
Although research is still emerging and many uncertainties remain, there is growing evidence that seabed disturbance caused by bottom trawlers may have released significant amounts of CO₂ over time. This suggests that bottom trawling likely contributes far more to the climate crisis than other types of fishing.
The full scale of its impact - from both fuel consumption and sediment disruption - is still being assessed.
While bottom trawlers can catch far more fish per hour than many small-scale fishing methods, this apparent efficiency comes with significant costs. It often undermines environmental, social, and economic sustainability. If bottom trawling were to replace small-scale fishing, it could lead to widespread job losses in rural coastal communities - where alternative livelihoods are limited - while simultaneously degrading marine ecosystems that small-scale fishers and local communities depend on for food and income.
Bottom trawling can have both positive and negative social effects. On one hand, it provides employment for thousands of people and supplies food for millions. On the other hand, these benefits often come at the expense of small-scale fishers, who make up the majority of the global fishing workforce.
Bottom trawling can affect coastal communities by increasing competition for fish and fishing grounds, by damaging marine habitats and by reducing catches available to small-scale fishers. Trawl fisheries also often catch large amounts of unwanted marine life. Much of this catch is discarded dead or dying, including fish that could otherwise be eaten or caught by small-scale fishers. This waste can reduce food supplies and income opportunities for local communities, undermining livelihoods, food security and local economies.
The severity of social impacts depends on several factors:
While the environmental impacts of bottom trawling have been widely studied, its social impacts are less well documented. Historically, fisheries and conservation research has focused more on ecological impacts than on the social dimensions of environmental change. However, a growing number of studies - alongside many reports from fishers themselves - describe how bottom trawling affects livelihoods and coastal communities. Together, this evidence suggests that bottom trawling is part of a broader trend towards more industrialised fisheries, which often favour corporate, foreign and urban interests over small-scale coastal communities.
Food security refers to the availability of nutritious food and people’s ability to access it. Food insecurity and inadequate nutrition affect people of all ages, but have particularly harmful impacts on pregnant and lactating women and on the physical and cognitive development of children.
Fish is a cornerstone of food security in many low-income coastal communities, providing more than half of the animal protein consumed in many countries across Africa, Asia and the Pacific and serving as a key dietary staple in many regions.
The relationship between bottom trawling and food security is complex, context-specific and requires further study. Globally, bottom trawling accounts for roughly a quarter of marine wild-capture seafood production, illustrating the scale of the practice. However, the short-term benefits of high-volume, low-cost fisheries can come at the expense of long-term ecosystem health, small-scale fishers’ livelihoods and the resilience of local food systems. Declining fish populations could leave more than 10% of the global population vulnerable to micronutrient and fatty-acid deficiencies in the coming decades.
Even where fish stocks remain healthy, in many low- and middle-income countries a significant portion of bottom-trawl catches is exported to wealthier markets, diverting seafood away from communities that rely on it for food security. Increasingly, trawl catches are also used to supply the expanding aquaculture and livestock feed industries.
Where bottom trawlers and small-scale vessels operate in the same or nearby waters, they often target the same fish populations. Industrial trawl fleets can outcompete small-scale fishers by catching large volumes of fish and directing catches to export markets. Where bottom trawling has contributed to habitat damage and declining fish populations, less fish remains available for small-scale and subsistence fishers, reducing local access to protein and dietary diversity.
Bottom trawling has widespread direct and indirect social impacts on coastal communities, with small-scale fishers and fishworkers bearing the greatest impacts of bottom trawling. These impacts are typically driven by increased competition for sea space and resources, as well as the degradation of marine ecosystems on which small-scale fishers depend. Six social outcomes are commonly associated with the introduction or expansion of bottom trawling on small-scale fishing communities:
Small-scale fishers struggle to compete with industrial trawlers, which are larger and typically have greater financial resources and technological capacity. The presence of bottom trawlers can reduce fish availability, lower profits, and force some to leave the sector, affecting local markets and food security.
Bottom trawling can also erode the social fabric of fishing communities by displacing fishers from traditional fishing grounds or damaging habitats so severely that they no longer support customary fisheries. Over time, disruption to traditional practices and associated knowledge systems can have lasting impacts on the way of life of coastal communities. In regions where trawling occurs near areas inhabited by Indigenous peoples, conflicts can arise over the rights of these communities. These may include disruptions to Indigenous fishing practices, impacts on land and fishing rights, and damage to cultural heritage.
Coastal countries often sell the right to fish their waters to foreign countries, via fishing access agreements. These agreements can increase competition with local fishers for access to space and resources, and financial benefits rarely trickle down to coastal communities.
Bottom trawl vessels with access agreements predominantly target fish for export markets, which diverts protein and nutrients away from local markets. This can threaten coastal livelihoods, food security and communities’ economic growth. These agreements generally do not require catches to be landed in the host countries, diverting yet more economic opportunities for processing and trade.
The economic benefits gained from such agreements often stay within central governments, rather than being reinvested into the long-term livelihoods and economic growth of the coastal communities directly affected by the arrival of new industrial fishing vessels.
Bottom trawling is a costly activity. Large vessels and bottom trawling gear are expensive to buy and maintain, and dragging weighted nets across the seabed consumes large amounts of fuel. Government subsidies help bottom trawling companies remain profitable despite these costs; without them, many of the world’s bottom trawlers would operate at a loss. These subsidies use public money to reduce operating costs, such as fuel, giving large industrial fleets an advantage over small-scale fishers, who receive far less public investment.
This is particularly true of distant water bottom trawling enterprises, which fish in the waters of foreign countries. Many of the world’s distant water fisheries would not be profitable without government subsidies. Subsidised bottom trawling companies rarely reinvest in the coastal communities that are directly affected by their damaging activities, while distant water fishing vessels may not even make landfall in the country whose resources they are exploiting.
In 2022, members of the World Trade Organization reached a historic agreement to address harmful fisheries subsidies, including those supporting illegal, unreported or unregulated fishing, fishing of overfished stocks, and fishing in the high seas. This entered into force in September 2025 following ratification by two-thirds of member states. Further work is now needed to ensure effective implementation of the agreement, address the issue in countries that have not yet ratified it, and continue work to further tackle subsidies that contribute to overfishing.
Over 140 members. 52 countries. One shared mission. Discover the people, campaigns, and stories driving real change for our oceans.
Keep up to date with the coalition’s latest news, events and campaigns. By signing up to the newsletter you agree to receive emails from the Transform Bottom Trawling Coalition on issues related to coalition. Your contact information will not be shared or publicised.
