Ocean Breathing

INTRODUCTION

The seafloor is not an empty landscape. It contains complex habitats formed by sediments, reefs, corals, sponges, burrowing animals and countless other organisms that create shelter, feeding grounds and nursery areas for marine life.

Bottom trawling is a fishing method in which large nets and associated gear are towed across or close to the seabed to catch fish and shellfish living near the ocean floor.

When fishing gear makes contact with the seabed, it can disturb sediments and damage organisms and physical structures. The severity of these effects varies considerably depending on the type of fishing gear, how frequently an area is trawled and the characteristics of the seabed.

Some naturally dynamic sandy or muddy habitats can be relatively resilient to disturbance. Other environments — particularly deep-sea habitats and areas containing slow-growing corals, sponges and other structure-forming organisms — can be much more vulnerable.

Understanding bottom trawling therefore requires looking beyond the fish that are caught. It also means understanding what happens to the ecosystem beneath the net.

This reflects NOAA and FAO assessments of seabed disturbance from bottom-contact fishing gear.

WHY IT MATTERS

The seabed is habitat. Seafloor structures provide shelter, feeding areas and nursery habitat for fish and invertebrates. Damage to this habitat can therefore affect organisms throughout the wider ecosystem.

Seabed biodiversity can be reduced. Repeated trawling can reduce the abundance, biomass, diversity and productivity of organisms living on or within the seabed.

Some habitats recover very slowly. Deep-sea corals, sponges and other long-lived organisms can take decades or longer to develop. Repeated disturbance can prevent complex habitats from fully recovering.

The impacts extend beyond individual species. Altering seabed structure can affect predator-prey relationships, nursery habitat, food availability and other ecological processes.

Marine sediments also participate in Earth’s carbon cycle. Seabed disturbance can resuspend and redistribute organic carbon stored in sediments. Scientists are actively studying how intensive trawling affects long-term carbon storage and cycling.

Protecting seabed ecosystems is therefore not simply about conserving what lies on the ocean floor. It is about maintaining the physical and biological foundation supporting wider marine ecosystems.

NOAA documents reductions in benthic abundance, biomass and diversity from seabed disturbance, while recent research also shows intensive trawling can alter sediment carbon storage and cycling.

KEY FACTS

Bottom trawling contributes roughly one quarter of global marine fisheries landings.

Its environmental impact varies dramatically between habitats. Naturally disturbed seabeds can be more resilient, while stable deep-water habitats and coral-dominated environments are generally much more vulnerable.

Bottom-contact gear can alter the physical structure of the seabed. Trawling and dredging can flatten seabed features and disturb organisms living on and within sediments.

Complex seabed habitats support fish populations. Corals, sponges and other structures provide shelter and feeding habitat, including for commercially important species.

Repeated disturbance matters. An ecosystem disturbed again before it has recovered can experience greater long-term changes than an ecosystem subjected to infrequent disturbance.

Bottom trawling can influence seabed carbon processes. Scientific research shows that sediment mixing, resuspension and changes in benthic communities can alter natural carbon flows.

The approximately one-quarter figure and habitat-sensitivity distinction come from NOAA; FAO reviews document physical and biological impacts of towed fishing gear. NOAA Fisheries

Main Threats

Physical disturbance of the seabed. Trawl doors, ground gear, chains and other components can scrape, penetrate or disturb the ocean floor as fishing gear moves across it.

Loss of habitat complexity. Damage to corals, sponges and other structure-forming organisms can transform complex three-dimensional habitats into simpler environments with fewer places for marine organisms to shelter and feed.

Repeated trawling. Even where individual disturbances are recoverable, frequent trawling can occur faster than ecological recovery, potentially maintaining habitats in a persistently disturbed state.

Expansion into vulnerable habitats. Modern navigation and fishing technology can allow vessels to operate in areas that were previously difficult to access, increasing concern about deep-water and other sensitive environments.

Bycatch. Bottom trawls can unintentionally capture non-target fish, marine mammals, sea turtles and other organisms. The scale and composition of bycatch vary greatly among fisheries.

Sediment resuspension. Bottom-contact fishing can lift sediment into the water column, potentially changing seabed processes and affecting water clarity and benthic organisms.

The environmental consequences are therefore strongly dependent on where, how and how often bottom trawling occurs.

NOAA specifically describes habitat alteration and protected-species bycatch risks, while FAO reviews emphasize that effects depend strongly on gear and seabed conditions. NOAA Fisheries

SOLUTIONS

Protect vulnerable seabed habitats. Spatial closures can keep bottom-contact fishing away from deep-sea corals, sponge grounds, nursery areas and other ecosystems that are particularly sensitive to disturbance.

Map the seafloor before managing fishing activity. Better habitat mapping can identify vulnerable areas and help fisheries managers distinguish resilient fishing grounds from ecosystems requiring stronger protection.

Reduce the trawling footprint. Concentrating fishing activity in appropriately managed areas while protecting sensitive habitats can reduce the total seabed area exposed to disturbance.

Improve fishing gear. Modifications to trawl doors, ground gear and other components can reduce seabed contact or decrease unwanted catches in some fisheries.

Use alternative fishing methods where practical. Depending on the target species and fishery, traps, pots, longlines, gillnets or other techniques may sometimes provide alternatives with different seabed impacts.

Manage fisheries scientifically. Sustainable catch limits, effort controls, spatial management and effective monitoring can reduce both overfishing and unnecessary habitat disturbance.

Monitor recovery. Protected or closed areas should be scientifically monitored so managers can understand how different seabed habitats recover after trawling pressure is reduced.

The goal is not simply to replace one fishing method everywhere. Effective management should match fishing practices to ecosystem vulnerability while maintaining sustainable food production and livelihoods.

FAO identifies gear modification, spatial controls, effort management and alternative gears among mitigation options; NOAA similarly emphasizes that management must account for local habitat sensitivity. FAOHome

WHAT YOU CAN DO

Choose seafood with credible sustainability information. Where possible, learn how seafood was caught and whether the fishery manages both fish populations and habitat impacts.

Ask how seafood is produced. Retailers, restaurants and seafood suppliers can help make fishing methods more visible to consumers.

Support protection of vulnerable marine habitats. Deep-sea corals, sponge grounds, seamounts and important nursery habitats can benefit from restrictions on destructive bottom-contact activities.

Support science-based fisheries management. Sustainable fisheries depend on reliable data, monitoring, enforcement and management that considers both target species and the ecosystems supporting them.

Reduce seafood waste. Using seafood efficiently reduces unnecessary pressure on marine resources regardless of the fishing method used.

Support ocean mapping and research. Large areas of the seabed remain poorly understood. Better mapping and ecological research can help identify habitats that are particularly vulnerable to disturbance.

Share the full story. Bottom trawling is neither identical everywhere nor environmentally harmless. Its impacts depend on habitat, gear, fishing intensity and management. Communicating that nuance helps create better ocean policy.

SOURCES

NOAA Fisheries — To Manage Global Trawling Impact, Think Local
Overview of bottom-trawling impacts, habitat sensitivity and the importance of locally appropriate fisheries management. NOAA Fisheries
NOAA Fisheries — Global Trawling Impact

NOAA Fisheries — Fishing Gear: Bottom Trawls
Explanation of bottom-trawl gear, target species, protected-species risks and bycatch-reduction measures. NOAA Fisheries
NOAA Fisheries — Bottom Trawls

NOAA Fisheries — Protecting Fish Habitat Helps Put Food on Your Table
Explains why seabed habitats matter to fish and how towed fishing gear can affect them. NOAA Fisheries
NOAA Fisheries — Protecting Fish Habitat

FAO — Impacts of Trawling and Scallop Dredging on Benthic Habitats and Communities
Technical review of the physical and biological effects of towed fishing gear on seabed ecosystems. FAOHome
FAO — Impacts of Trawling and Scallop Dredging

FAO — Options to Mitigate Bottom Habitat Impact of Dragged Gears
Technical review of gear modifications, alternative fishing methods and other approaches for reducing seabed impacts. FAOHome
FAO — Mitigating Bottom Habitat Impacts

Nature Geoscience — Long-term Carbon Storage in Shelf Sea Sediments Reduced by Intensive Bottom Trawling
2024 research examining how intensive bottom trawling can affect organic-carbon cycling and long-term storage in marine sediments. Nature
Nature Geoscience — Bottom Trawling and Sediment Carbon

Bottom Trawling & Seabed Destruction