Maarg Manthan · Topic 13.21

Bottom Trawling and Its Impact on Deep-Sea Fishing

Environment & Ecology › Air, Marine, Noise and Other Pollution · Topic 13.21

Bottom trawling is a fishing method in which a large net, held open by weighted boards and fitted with heavy ground gear, is dragged along or just above the sea floor to catch fish and shrimp that live on or near the bottom. It is productive and widely used, including by India's mechanised fleets, but it is among the most destructive forms of fishing. The gear scrapes and crushes seabed habitats such as seagrass, sponges, corals, and cold-water coral reefs; stirs up sediment; releases stored carbon; and catches large amounts of unwanted species and juveniles as bycatch, including turtles, rays and sharks, much of which is thrown back dead. Deep-sea bottom trawling, which targets slow-growing, long-lived fish on seamounts and slopes, can wipe out communities that take decades or centuries to recover. In India, marine fishing regulation is a state subject; states follow a 61-day uniform monsoon fishing ban from 2020 (15 April to 14 June on the east coast and 1 June to 31 July on the west coast), mesh-size limits, turtle excluder devices and zones that keep trawlers away from traditional fishers.

5 min read · UPSC Prelims · Environment & Ecology · Air, Marine, Noise and Other Pollution

At a Glance

Method Net dragged on sea floor
Main harm Habitat damage, bycatch
Indian ban 61 days in monsoon
Device Turtle excluder
Regulation State subject
Exam link UPSC Prelims, Environment & Ecology: Air, Marine, Noise and Other Pollution

Where Does It Fit?

This topic ties fishing to marine pollution and habitat destruction. It is the penultimate topic of the macro on pollution, before electromagnetic fields from mobile towers. Previous topic: Respiratory Irritants and Toxic Chemicals in Air Pollution. Next topic: Mobile Tower Radiation and Electromagnetic Field (EMF) Concerns.

How Does Bottom Trawling Harm Marine Ecosystems?

Impact	Details
Habitat destruction	Heavy gear flattens corals, sponges, seagrass and rocky habitats that shelter fish
Bycatch	Unwanted fish, turtles, sharks, rays and juvenile fish are caught and often discarded dead
Overfishing	Catching juveniles and breeding fish reduces stocks
Sediment disturbance	Plumes of mud smother filter feeders and may release stored carbon
Deep-sea damage	Slow-growing, long-lived species on seamounts and slopes recover very slowly
Food chain change	Loss of predators and bottom life changes marine food webs
Social conflict	Competition with small-scale and traditional fishers

How Is Trawling Regulated?

Monsoon fishing ban: 61 days a year, from 15 April to 14 June on the east coast and 1 June to 31 July on the west coast, since 2020
Marine Fishing Regulation Acts: coastal states regulate trawling, mesh size, zones and licences
Territorial limits: mechanised vessels are kept out of a near-shore zone reserved for traditional fishers
Turtle excluder devices: grids in trawl nets that let turtles escape
Mesh size limits: larger mesh lets small fish escape
Deep Sea Fishing in the EEZ: Indian policy encourages use of long-line and gill nets instead of bottom trawls for deep sea tuna
Global action: UN General Assembly resolution 61/105 of 2006 calls for protection of vulnerable deep-sea ecosystems from bottom fishing
Schemes: Pradhan Mantri Matsya Sampada Yojana supports sustainable fisheries and fleet change

What Else Should You Remember?

Trawl net: cone-shaped net towed by a boat
Otter boards: heavy panels that keep the trawl net mouth open
Ground gear: chains and rollers along the net bottom
Bottom trawl vs midwater trawl: bottom trawls scrape the sea floor, while midwater trawls fish higher up
Shrimp trawling: has some of the highest bycatch ratios
Discards: bycatch thrown overboard, often dead
Trawl intensity: some shelf areas are trawled many times a year
Carbon release: trawling can disturb carbon-rich sediments
Seamounts: underwater mountains hosting slow-growing corals and fish
Cold-water corals: take centuries to form reefs
Orange roughy: a long-lived deep-sea fish heavily depleted by trawling
High seas: areas beyond national jurisdiction, where regional fishery bodies set rules
Regional Fisheries Management Organisations: bodies such as SIOFA in the southern Indian Ocean
Palk Bay conflict: bottom trawling by Tamil Nadu boats in Sri Lankan waters has caused disputes and arrests of fishers
Kerala: restricts trawling in near-shore waters and bans pair trawling
Pair trawling and purse seining: banned or restricted in several states
Light and bull trawling: use of lights and pair trawlers is restricted
Ghost gear: lost trawl nets keep catching fish
Marine protected areas: no-trawl zones help ecosystems recover
Alternative gear: traps, hook and line and selective nets lower bycatch
Fish stock assessment: ICAR-CMFRI in Kochi studies marine fish stocks
Blue economy: sustainable fisheries are part of India’s blue economy plans
Link to previous: see Thermal Pollution: Causes, Effects and Control
Link to next: see Mobile Tower Radiation and Electromagnetic Field (EMF) Concerns
Link to marine areas: see Important Coastal and Marine Biodiversity Areas
Caution: ban dates and rules change; check current notifications of the state and the Centre
Exam hint: remember habitat harm, bycatch, TED and the 61-day ban
Habitat destruction: trawl doors and ground gear flatten structures that give shelter to young fish and invertebrates
Recovery times: soft sediment habitats may recover in months or years, while corals and sponges can take decades to centuries
Selective gear and closures: grids, escape panels, larger mesh and closed areas are the most proven tools to cut bycatch

Why Does It Matter for the Exam?

Harm: Habitat and bycatch
Device: TED
Ban: 61 days
Current affairs link: Deep sea fishing and Palk Bay
Common errors: confusing bottom trawling with purse seining

As an analytical point, bottom trawling shows the conflict between short-term catch and long-term ocean productivity. Limits on gear, protected no-trawl zones and support for small-scale fishers give better results than catching more from the same sea floor.

Why Is This Topic Important?

Method Drag net
Harm Habitat, bycatch
Fix Gear, zones

What Came Next?

The next topic covers mobile tower radiation and electromagnetic field concerns. Next topic: Mobile Tower Radiation and Electromagnetic Field (EMF) Concerns.

Key People and Terms

Bottom trawl Net dragged on sea floor
Bycatch Unwanted catch
TED Turtle excluder device
EEZ Exclusive economic zone
Seamount Underwater mountain
RFMO Regional fishery body

Exam Corner

Points to Remember

Net dragged on the sea floor.
Big problem: bycatch.
Monsoon ban: 61 days.
TED helps turtles.
Fishing rules are a state subject.

Do Not Confuse With

Bottom trawling and purse seining Dragging on bottom versus encircling surface fish
Bycatch and discards Unwanted catch versus what is thrown back
EEZ and high seas National waters versus beyond jurisdiction

Memory Hook

Drag the floor, crush the home, bycatch dies, ban for sixty-one days.

Mains Angle

Questions ask for impacts and regulation. These points help.

Harm Habitat, bycatch
Rules Ban, gear
Way Selective gear

A Question You May Face

An original practice question, not a past paper question.

“Examine the ecological impact of bottom trawling and the regulatory measures taken in India and globally.”

How to Answer

Method Drag net.
Harm Habitat, bycatch.
Rules Ban, TED.
Way Selective.

GS Relevance

Prelims: trawling, bycatch, bans, devices. GS Paper 3: marine resources and fisheries management.

Frequently Asked Questions

What is bottom trawling?

Bottom trawling is a fishing method in which a weighted net is dragged along the sea floor to catch fish, shrimp and other animals living on or near the bottom. It catches large quantities of fish but damages seabed habitats and catches many unwanted species as bycatch, so it is one of the most criticised fishing methods.

Why is bottom trawling harmful to the environment?

The heavy gear crushes corals, sponges, seagrass and other seabed life that provide shelter for fish. It also disturbs sediments and may release stored carbon, and it catches large numbers of juveniles, turtles, sharks and rays as bycatch, much of which is thrown back dead. Deep-sea communities may need decades to recover.

What is the monsoon fishing ban in India?

India has a uniform 61-day ban on fishing by mechanised vessels in its territorial waters during the monsoon breeding season, which since 2020 runs from 15 April to 14 June on the east coast and 1 June to 31 July on the west coast. It protects spawning fish and gives stocks time to recover; traditional non-motorised boats are usually exempt.

What is a turtle excluder device?

A turtle excluder device is a grid with an escape opening fitted in the neck of a trawl net. Small fish and shrimp pass through the grid into the net's end, while larger animals such as sea turtles hit the grid and are guided out through the opening. India requires it for trawlers in many areas to reduce turtle deaths.

How is deep-sea bottom trawling regulated globally?

UN General Assembly resolution 61/105 of 2006 and later resolutions called on states and regional fishery bodies to protect vulnerable marine ecosystems such as seamounts and cold-water corals from bottom fishing. Regional fisheries management organisations have closed some areas, but enforcement on the high seas is difficult and coverage is partial.

PYQ Practice — Statement Analysis

1 Bottom trawling drags a net along the sea floor.

True

It damages habitats.

2 The Indian monsoon fishing ban lasts 61 days.

True

Since 2020.

3 Turtle excluder devices trap turtles.

False

They let turtles escape.

4 Fisheries rules in territorial waters are a Union subject only.