Bottom Trawling Q&A
What is trawling?
Trawling is a fishing method that is used to catch approximately 20 million tons of fish per year – about a quarter of all the fish caught in the world. Trawling is an efficient method of catching fish; it is widely used for commercial fishing because of its efficiency.
How does trawling work?
The process involves a fishing vessel, known as a trawler, towing a trawl net through the water. The design of the net varies based on the type of trawling, but it typically includes a wide opening to guide fish into a narrowing section (the codend) where they are trapped. Trawl nets can be deployed horizontally, vertically, or along the seabed, depending on the species being targeted.
What is bottom trawling?
The method involves towing the net along the seabed to catch species that live on or close to the seabed. In South Africa these species include hake, sole, kingklip and monk, and other incidentally caught bycatch species.
Are SADSTIA members involved in bottom trawling?
Yes. The 37 members of the South African Deep-Sea Trawling Industry Association own and operate 53 trawlers that are licensed to fish in South Africa’s exclusive economic zone.
Watch this short film to find out more about trawling in South Africa – where it occurs, how it is regulated and the work that is done to minimise impacts on the marine ecosystem.
How can SADSTIA members claim to be responsible when they are engaged in bottom trawling?
Poorly managed bottom trawl fisheries can have significant impacts, whereas well-managed fisheries can be sustainable. Well-managed fisheries monitor stock status, restrict overfishing, protect sensitive species and habitats and enforce rules. Good management stays up to date with new science, data and information and quickly adapts regulations to changing conditions. The South African trawl fishery for hake satisfies all these requirements. It has been certified sustainable and well-managed by the Marine Stewardship Council for 21 years. The fishery has been audited annually and was re-assessed in 2009, 2015 and 2020, each time securing the highly respected MSC certification. In 2025, it will begin another demanding re-assessment in pursuit of a fifth five-year certification. The MSC’s Fisheries Standard is rigorous and takes into account the entire fishery and the ecosystem on which it depends.
Some of the unique features of the management of the South African trawl fishery for hake include:
- Scientific observers accompany 9% of fishing voyages in the deep-sea trawl fishery and 8% of voyages in the inshore trawl fishery. The data collected by scientific observers contributes substantially to the annual audits and five-yearly assessments that are conducted on behalf of the MSC.
- The trawl fishery for hake is managed by total allowable catch, meaning an absolute limit is set on the amount of fish that can be caught by hake trawlers in one season.
- The fishery is effort controlled, meaning the number of trawlers is strictly limited and the fleet can’t grow too big for the available resources.
- The size and type of trawl gear is regulated and monitored. For example, minimum mesh size regulations aimed at minimising the catch of juvenile fish have been in place for 60 years. Limits on the size and weight of bobbins and footropes were first introduced 20 years ago, to reduce the impacts of fishing on seabed habitats.
- In 2008, the trawl grounds were ring-fenced to prevent the expansion of trawling operations beyond areas that had already been impacted. The ring-fenced area is monitored by a vessel monitoring system and compliance is good.
- Hake trawlers respect the boundaries of 12 marine protected areas that occur inside the trawl ring fence. Seabed Management Areas that protect specific habitat types have also been recognised and are being voluntarily avoided by the fishery.
- Mitigation measures to reduce the interaction of seabirds with trawl gear include vessel-specific management measures, the mandatory deployment of bird-scaring lines (that keep seabirds away from the danger zone at the rear of the vessel) and regulations for the greasing of trawl warps.
- Bycatch it processed for sale and discards are closely monitored by fisheries observers. Bycatch limitation measures have been introduced and include precautionary upper catch limits for valuable bycatch species, kingklip and monk, and move-on rules.
How is technology improving trawling practices?
- The trawl fleet is constantly and consistently monitored by satellite to ensure compliance with the boundaries of the trawl ring-fence and marine protected areas.
- Sonar (“fish finders”) is used by fishing captains to target hake and limit bycatch.
- On-board cameras and artificial intelligence are increasingly used to monitor catches in real time.
- An electronic tension sensor that checks that seabird scaring lines are properly deployed, is being tested in the fishery.
- The trawl fishery for hake is testing a system that enables the recycling of used fishing nets.
These innovations aim to balance efficiency with environmental responsibility.
What about claims that bottom trawling produces as much carbon emissions as air travel?
Dragging heavy nets along the ocean floor requires substantial diesel fuel. Bottom trawling produces an average of 4.65 kg of CO₂ per kilogram of seafood, making it one of the more carbon-intensive fishing methods. This is roughly double the carbon footprint of chicken but only a quarter that of beef.
Carbon emissions vary significantly depending on how each fishery operates. Factors like how often gear contacts the seafloor and how deeply it penetrates affect fuel consumption, as does the type of seabed being trawled. However, the most important factor is the quality of fishery management: well-managed fisheries with healthy fish stocks use far less fuel. When fishers aren’t racing to catch fish before competitors, fuel consumption drops dramatically.
Since nearly all seafood carbon emissions come from fuel use, fishing emissions will continue improving as fleets modernise.
Debunking the aviation comparison
Claims that bottom trawling produces as much carbon as aviation stem from a flawed 2021 study that has been thoroughly discredited. The researchers incorrectly assumed that carbon in seafloor sediments acts as a permanent storage that gets released when trawling disturbs it.
This assumption was wrong. Nearly all seafloor carbon is naturally broken down by microbes and other organisms regardless of fishing activity. The authors ignored this fundamental biological process.
In 2022, scientists measured actual carbon levels in trawled versus untrawled areas rather than relying on flawed models. They found no significant differences between the two, and some trawled areas actually contained more stored carbon because fishing had removed organisms that naturally break it down.
Bottom trawling’s climate impact comes solely from vessel fuel consumption, not from releasing stored carbon. The dramatic comparisons to aviation were based on faulty science.
How does bottom trawling compare to other forms of food production?
Bottom trawling isn’t the most environmentally friendly way to produce food, but it performs better than several alternatives when properly managed. Well-managed bottom trawl fisheries rank among the lowest-impact food sources globally, and many are steadily improving their practices.
Like all seafood production, bottom trawling offers significant environmental advantages over land-based protein sources. It requires no fresh water, fertilisers, or agricultural chemicals. There’s no risk of nutrient runoff polluting waterways, and no natural ecosystems need to be converted into farmland.
Seafood generally ranks among the most sustainable proteins available, though environmental impact varies considerably depending on the species caught and the fishing methods used. Bottom trawling does consume more fuel than most other fishing techniques, but the overall impact depends heavily on two key factors: which species are being targeted and how effectively the fishery is managed.
When fish populations are healthy and abundant, they require less fuel and effort to harvest. This means that maintaining biological sustainability (keeping fish stocks at robust levels) directly contributes to reducing the overall environmental footprint of bottom trawling operations.
What impact does bottom trawling have on seafloor habitats?
Most trawling occurs over gravel, sand, or mud where each pass kills between 5% to 26% of bottom-dwelling invertebrates. These areas recover at rates of roughly 29% to 68% annually. Compared to land-based farming – where habitat destruction is nearly 100% and recovery takes centuries – bottom trawling can be relatively sustainable.
Effective management focuses on allowing fished areas time to recover and protecting sensitive habitats through closures or restrictions.
Research shows that well-managed trawling preserves seafloor habitats effectively. A 2022 global review found that in most managed bottom trawl areas, over 80% of seafloor life remains intact. The main exception was the Adriatic Sea, which has suffered from poor management for decades.
Are the claims in the film Ocean with David Attenborough correct?
Several misconceptions about bottom trawling persist, often fuelled by selective footage and dramatic narratives that don’t reflect the full picture.
Myth: Bottom trawling is universally destructive.
Fact: Impact depends entirely on management quality and location.
Myth: Fishing is the ocean’s biggest threat.
Fact: Global impact assessments consistently show that carbon emissions, ocean acidification, sea level rise, shipping and terrestrial pollution cause far greater damage to marine ecosystems than fishing.
Myth: Marine protected areas are the best solution.
Fact: MPAs work well for protecting small, sensitive, or culturally important areas, but they’re not a universal solution.
Myth: Ocean food production is inherently unsustainable.
Fact: The ocean is generally better for food production than land.
What are the alternatives to trawling?
Trawling produces 20 million tons of animal protein per year. If trawling is banned, how will the global food system compensate? Replacing bottom trawled protein with a typical livestock mix of 30% beef, 33% pork and 37% chicken would require land clearing equivalent to half the Amazon rainforest.
What is the future of trawling?
The future of trawling lies in adopting more sustainable practices and technologies. Education, regulation and innovation are key to reducing its environmental footprint while ensuring the long-term viability of global fisheries. Consumers also play a role by choosing sustainably sourced seafood, such as trawl-caught, MSC-certified South African hake.
Find out more
SADSTIA members participate in a sustainable, MSC-certified fishery, provide approximately 12 400 jobs and deliver R8.5 billion to the South African economy every year.
The science of sustainable seafood explained by scientists at the University of Washington, United States of America.
A bi-annual publication from the Food and Agriculture Organization of the United Nations that highlights trends and summarises the status of fisheries and aquaculture around the world.