Technical ReportPDF Available

New perspectives on an old fishing practice: Scale, context and impacts of bottom trawling

December 2021

DOI:10.13140/RG.2.2.12318.41286/1

Authors:

The Pew Charitable Trusts

A report by leading fisheries experts shares novel analysis on the scale, context, and impacts of the age-old fishing practice of bottom trawling. The report shares new data and analysis combined with policy recommendations to inspire constructive action around this controversial practice.

Bottom trawling gears and related towed demersal fishing gears

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National and global-level comparisons of environmental impacts of different fishing gears

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Global catch by gear type (within EEZs)

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Top 10 bottom trawling countries by total catch and percentage of global catch.

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Top 10 countries ranked by the percentage of their total EEZ catch from bottom trawling gears.

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Figures - uploaded by Daniel Steadman

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Content uploaded by Daniel Steadman

Content may be subject to copyright.

New perspectives on an old shing

practice: Scale, context and impacts

of bottom trawling

AUTHORS

Daniel Steadman1, John B. Thomas2, Vanessa Rivas Villanueva2, Forrest

Lewis2, Daniel Pauly3, M.L. Deng Palomares3, Nicolas Bailly3, Max Levine2,

John Virdin4, Steve Rocliffe5, Tom Collinson6

REPORT 2021

New perspectives on an old shing practice: Scale, context and impacts of bottom trawling2

AUTHORS

Daniel Steadman1, John B. Thomas2, Vanessa Rivas Villanueva2, Forrest Lewis2, Daniel Pauly3,

M.L. Deng Palomares3, Nicolas Bailly3, Max Levine2, John Virdin4, Steve Rocliffe5, Tom Collinson6

1 Fauna & Flora International, The David Attenborough Building, Pembroke Street, Cambridge,

CB2 3QZ, UK

2 CEA Consulting, Montgomery Street, San Francisco, CA 94104, USA

3 Sea Around Us, Institute for the Ocean and Fisheries, University of British Columbia,

Vancouver, BC, V6T 1Z4, Canada

4 Ocean & Coastal Policy Program, Nicholas Institute for Environmental Policy Solutions,

Duke University, Durham, NC, USA

5 Blue Ventures, The Old Library, Trinity Road, Bristol, BS2 0NW, UK

6 Blue Ventures, The Old Library, Trinity Road, Bristol, BS2 0NW, UK

CONTRIBUTIONS

DS, JT, VRV, and FL conceptualized the report and coordinated its writing, editing, and review.

DP, MLDP, and NB provided the reconstructed catch data and provided thought partnership

for the report, as well as long-term investments into the SAU platform. ML provided expertise

on bottom trawling in China and edited the report. JV contributed original content through the

West Africa case study, guidance on methods for the social impacts section, and substantial

comments on the report draft. SR and TC provided additional comments on the report draft.

The authors would also like to thank Celeste Leroux of Virgil Group for her thought partnership,

Mark Michelin of CEA Consulting for his review of materials, and Comms Inc. for its copy

editing, report design, translation, and other communications support. Funding for this report

was provided by Oceans 5, Oak Foundation, and Oceankind.

Cover photographs (clockwise from top left): Sam Elliott/OceanMind, FFI, FFI, COAST, Paul Kay, Roger Bruget

New perspectives on an old shing practice: Scale, context and impacts of bottom trawling 3

Contents

Executive summary 4

1. Introduction 7

2. Denitions and historical context 10

3. State of the evidence: environmental impacts 14

4. State of the evidence: climate impacts 19

5. State of the evidence: socio-economic impacts 22

6. Global extent 28

7. Paths forward 35

References 40

New perspectives on an old shing practice: Scale, context and impacts of bottom trawling4

Executive summary

Bottom trawling is a globally widespread shing practice

responsible for 26 percent of the total marine sheries

catch.1 Bottom trawling is a method for catching aquatic

animals that involves dragging a weighted net or rigid

structure from a vessel along the seaoor. It is fundamental

to the supply of a multitude of food (shrimp, whitesh,

atsh) and non-food (shmeal and sh oil) commodities.

It has played an outsized role in the industrialization and

globalization of the shing sector, becoming a mainstay

of shery economies in Europe, North America, South

and Southeast Asia, East Asia, and West Africa. The vast

majority of the sh caught by bottom trawlers (99 percent)

is caught under the jurisdiction of coastal countries, in their

exclusive economic zones (EEZs).

Bottom trawling has always attracted opposition and

controversy. From 14th century “proto-trawling” to modern

shrimp trawling, these sheries have been consistently

associated with social conict (particularly in displacing

traditional shing practices), environmental degradation

1 This statistic includes catch caught both in the exclusive economic zones of countries

(EEZs) as well as on the high seas. Bottom trawling is also responsible on average for 26

percent of the catch within EEZs globally. There is also some bottom trawling in freshwater

sheries (e.g., Lake Victoria) but that practice is not included in this report.

(in terms of contact with and penetration of the seabed

as well as impacts on sensitive species) and lack of

selectivity (in terms of indiscriminately catching a range of

species). As a result, those involved with the practice have

at times sought to minimize or obfuscate some of these

impacts, while those seeking to limit it have sometimes

been hyperbolic and unrealistic in their criticisms and

solutions. Yet there is a surprising level of consensus

among the shing industry, researchers, governments,

civil society, and NGOs that bottom trawling presents

unique and critical challenges to environmental, social, and

climate goals for sheries.

This report seeks to provide new perspectives on this

historical controversy by presenting the most up-to-

date synthesis of available data and evidence on bottom

trawling’s extent, impacts, and solutions in order to inform

constructive policy-making. Specically, it uses novel data

analysis from Sea Around Us to map the global extent of

bottom trawling; a synthesis of peer-reviewed literature

to elucidate environmental, social, and climate impacts;

and insights from more than 40 global experts on what a

constructive future might look like that manages or severely

New perspectives on an old shing practice: Scale, context and impacts of bottom trawling 5

EXECUTIVE SUMMARY

limits the worst impacts of this practice, while also ensuring

a just and equitable society and a healthy food system.

Key ndings of the report include:

• Bottom trawlers catch 26 percent of the total global

marine sheries catch. In the most recent decade for

which there is data (2007-20162), more than 99 percent

of all bottom trawling occurs in the EEZs of coastal

countries, and less than 1 percent on the high seas.

The total amount of seafood caught by bottom trawling

annually in EEZs is roughly equivalent to all of the

seafood caught by the world’s artisanal shers.

• Bottom trawling is most intense (as measured by

catch per unit area) within the territorial seas of

coastal states. Approximately 20 percent of bottom

trawling within EEZs occurs less than 12 nautical miles

from shore (areas dened as territorial seas), despite

territorial seas making up less than 10 percent of total

EEZ area. The average trawling intensity in territorial

seas is on average double the average trawling intensity

within EEZs overall. Areas close to shore also tend to

be shed by artisanal and small-scale shers, which

may contribute to conict between artisanal shers and

industrial bottom trawlers.

• Asia is the locus of sh caught by bottom trawls; 50

percent of all bottom trawled sh is caught in the EEZs

of Asia or by the foreign eets of Asian countries. China,

Vietnam, Indonesia, India, and Morocco are the top ve

bottom trawling countries, as measured by average catch

over the most recent decade for which there is complete

data (2007-2016). China alone catches 15 percent of the

total bottom trawled catch. Whereas bottom trawling is

growing rapidly in Asia, it is declining or staying constant

in most other parts of the world.

• Distant water shing eets catch 22 percent of all the

sh caught by bottom trawlers in EEZs. These eets

are predominantly of Asian or European origin, and sh

in the EEZs of Africa and Oceania. In 34 countries –

mostly in Africa – over 90 percent of the catch caught

by bottom trawlers is caught by foreign-agged vessels.

These gures could be even higher, given the signicant

amount of distant water shing that is thought to be

illegal, unreported, or unregulated.

• There is general agreement that the environmental

impacts of bottom trawling represent unique

challenges when compared to other shing gears.

The practice stands alone among shing gears in that

it can be conclusively linked to all three of the major

impacts of shing on marine biodiversity: overshing,

bycatch, and seabed contact. It is the only gear type that

2 Since the bulk of the work on this report was completed, the Sea Around Us data have been

updated to 2018; the update did not alter any of the patterns and trends reported here.

requires sustained contact with and often penetration of

the seaoor in a manner that can degrade and destroy

marine habitats. Despite this agreement between

academia, NGOs, the shing industry, and sheries

managers, major areas of contention remain. These

include bottom trawling’s spatial footprint, the local

character of its impacts (historic and present-day), and

which solutions are viable or desired given competing

goals for sheries.

• Bottom trawling contributes to greenhouse gas

emissions through its high fuel use and the disturbance

of carbon-containing sediments on the seaoor. Of

the major gear types used in global sheries, bottom

trawling has the highest emissions from fuel use.

Seafood caught by bottom trawling has equivalent or

higher associated greenhouse gas emissions than most

meat, except lamb and beef. Novel, early-stage research

on the disturbance of sediments caused by bottom

trawling suggests it could contribute up to 1.46 Gt CO2-

eq in annual emissions, a level of emissions that would

put it on par with the aviation sector.

• Bottom trawling is also associated – positively and

negatively – with social impacts including economic

impacts, violence and conict, food security, human

rights abuses, and occupational health and safety.

While these impacts are not well studied and can vary by

context, bottom trawling presents a unique threat to the

livelihoods, cultural practices, and well-being of small-

scale shers, especially those in the tropics.

• Solutions to address environmental impacts of

bottom trawling typically fall into two categories:

efforts to manage impacts, and efforts to limit the

practice. Fisheries management measures have been

demonstrated to be effective in reducing (but not

eliminating) many negative environmental impacts from

bottom trawling, at relatively minimal social or economic

cost. However, the effectiveness of these measures is

largely a result of good governance – which tends to be

absent in the regions of West Africa and Asia where most

bottom-trawled seafood is currently caught. Efforts to

limit the practice can more comprehensively address the

full range of bottom trawling’s environmental impacts, but

they can be highly contentious and often do not include

viable social or economic solutions for those who are

displaced by the changes.

• More work is needed to identify solutions that can

avoid, minimize, or mitigate the social and economic

outcomes associated with bottom trawling. Although

an increasing number of frameworks and tools exist

to address the pervasive social challenges associated

with sheries more broadly, these frameworks are far

from being widely adopted and are not specic to the

New perspectives on an old shing practice: Scale, context and impacts of bottom trawling6

challenges associated with bottom trawling. Human

rights due diligence, exclusive access for small-scale

shers in nearshore waters, and just transition economic

packages are just some examples of solutions that

may help to guard against negative social or economic

outcomes for shers, shworkers, and others involved in

the sector.

• The marine conservation and sheries management

communities need to look beyond purely technical

measures for solving the challenges inherent to

bottom trawling. Bottom trawling is an entrenched

global practice, and solutions that fail to adequately

consider or address the key political, social, or

economic dynamics at play in the sector are unlikely to

succeed and will make it harder to achieve Sustainable

Development Goals associated with sheries.

Building on these insights, the report concludes with a set

of recommendations for constructive action, to transform

the status quo around bottom trawling (under the acronym

“TRANSFORM”). These recommendations for sheries

decision-makers, managers, shing industry leaders, and

advocates include:

• Transition the system: Bottom trawling supports a set

of complex, distinct food and non-food commodity

systems that are globally interconnected. Solutions

must consider broader dynamics – such as broad social

changes in shing culture, the rise of the global seafood

trade, and food consumption patterns – in order to avoid

unintended consequences, such as effort displacement.

Solutions to manage or limit bottom trawling should

not be viewed in isolation by policymakers, shery

managers, NGOs, or communities.

• Respect human rights: To catalyze meaningful

improvement in bottom trawl sheries requires a

human-centered approach. This means respecting both

the civil and political rights, as well as the economic,

social and cultural rights of those working in and

affected by such sheries. Bottom trawl sheries –

and policy changes relating to them – must abide by

a minimum standard of “do no harm.” More baseline

research into socio-economic impacts and possible

solutions (especially distributional impacts) should

accompany these efforts.

• Accelerate the transition to best practices: Modern

management practices – from gear innovation to

enhanced observer coverage – have dramatically

improved the performance of some bottom trawl

sheries, particularly in stabilizing overexploited stocks,

increasing selectivity, and reducing seabed pressure

especially in Vulnerable Marine Ecosystems (VMEs).

Urgent efforts are needed to export these practices to

regions that require them most, particularly in low and

middle-income countries in the tropics.

• Negotiate political action: Decision-makers must

recognize the unique biodiversity, climate and social

conict challenges associated with bottom trawling and

legislate for it as a special case – both through national

policies and international standards and agreements.

As well as making bold, gear-specic policy decisions,

this should also include acknowledging the signicant

investments and trade-offs needed to adequately

resource any transition away from bottom trawling.

• Stop harmful subsidies: Denitions of “harmful”

subsidies must include those accessed by specic

sheries using the highest impact practices, including

bottom trawl sheries. Conversely, subsidies supporting

transition out of (or to improve) practices such as

bottom trawling should be considered “benecial.”

• Freeze the footprint: Given the multitude of unresolved

challenges around bottom trawling – at global and

local levels – any new or expanded sheries should be

regarded as politically, socially, environmentally, and

economically inappropriate.

• Open up dialogue: Discourses around bottom trawling

from the sheries and conservation sectors do not

tend to emphasize common ground. Bold alliances

and painful but necessary compromise are needed to

meet the twin climate and biodiversity crises, including

between sectors with different material interests.

• Restrict appropriately: Ecologically and culturally

sensitive areas must be protected from bottom trawling

through a coherent area-based approach to such

sheries, encompassing inshore and offshore exclusion

zones as well as all classications of marine protected

areas (MPAs).

• Monitor impact to support adaptive management: While

all best-practice sheries require signicant volumes

of real-time information, bottom trawling management

(with its reliance on expensive and complex seabed

sensitivity data) necessitates robust, collaboratively

funded research. As well as near-term management-

focused monitoring, special attention should be directed

to emerging areas of trawling research, especially

life cycle analysis and carbon emissions arising from

seabed disturbance.

Executive summary

New perspectives on an old shing practice: Scale, context and impacts of bottom trawling 7

The Positive Disruption

Paradigm

Introduction

New perspectives on an old shing practice: Scale, context and impacts of bottom trawling8

1. Introduction

Marine sheries are a major component of global food

production, contributing 14 percent of edible food derived

from animals and forming a vital part of the aquatic

production system that supports the sustenance of 3.3 billion

people.i,ii These catches are the products of the ocean’s huge

and diverse ecosystems. Marine sh and crustaceans alone

make up nearly two-thirds of the biomass of all animal life on

Earth (nearly 190 times the biomass of all wild mammals and

birds).iii

Ensuring that sheries are environmentally sustainable,

socially equitable and have a minimal climate footprint

is central to creating a healthy, just society and a livable,

ourishing planet. Environmental, social, and climate goals

for sheries are enshrined in the United Nations’ Sustainable

Development Goals, particularly Goal 14 “Life below water”,

but also more socio-economically oriented SDGs including

Goal 1 “No poverty”, Goal 2 “Zero hunger”, Goal 10 “Reduced

inequalities”, and Goal 12 “Responsible consumption and

production”. Fisheries are also deeply connected to other

environmental goals such as those relating to climate change

and biodiversity, including Goals 13 and 15, “Climate action”

and “Life on land”.iv

Bottom trawling is one of the world’s dominant shing methods

and is responsible for 26 percent of the marine sh catch in

Exclusive Economic Zones (EEZs). Bottom trawling has played

an outsized role in the industrialization and globalization of

sheries, particularly the rapid transition from sail to steam to

diesel-powered trawling between the late 19th and early 20th

centuries, and the commensurate increases in marine sh catch

over the past century.v As a catching practice, it has become a

mainstay of shery economies in Europe, North America and

East Asia and has experienced a post-1950s boom in emerging

coastal economies in South and Southeast Asia and West Africa.

It is used to catch a multitude of food commodities (shrimp,

whitesh, atsh) and provides the raw sh required for several

important non-food commodities (sh meal and sh oil).

Over the course of this historical development, bottom

trawling has always attracted opposition and controversy.

From 14th century “proto-trawling” to modern shrimp trawling,

these sheries have been consistently associated with social

conict (particularly in displacing traditional shing practices),

environmental degradation (in terms of seabed pressure and

impacts on sensitive species) and lack of selection (in terms

of indiscriminately catching a range of species). Arguments in

support of or against trawling have frequently been reactive,

hyperbolic, and obfuscatory – pitting environmental groups and

small-scale shing communities against sheries managers and

the seafood industry, each group holding on ercely to its own self-

interest in lieu of compromise or common sense (See Table 1).

This section provides context for why bottom trawling

as a shing gear is both important and controversial, as

a foundation for why this report is needed at this time.

New perspectives on an old shing practice: Scale, context and impacts of bottom trawling 9

1. Introduction

Table 1 Common arguments for and against bottom

trawling

Common anti-trawling

arguments

Common pro-trawling

counterpoints

“Bottom trawling is an

unselective shing gear

that catches seafood

indiscriminately.”

“There is no other way to

catch these sh at a scale

demanded by the seafood

market.”

“Bottom trawl sheries can

be managed to reduce

environmental impacts.”

“Bottom trawling displaces

the livelihoods, cultural

practices, and food securi-

ty of small-scale shers.”

“Bottom trawling is an

ecient way to catch sea-

food in order to meet market

demand”

“Bottom trawling causes

widespread and often

irreversible harm to marine

seabed ecosystems.”

“Bottom trawling does cause

damage, but the impacts are

often not as bad or as

widespread as is claimed.”

“Certain areas that are

already heavily trawled

cannot be recovered and

are viable locations for

continued bottom trawling.”

While the issues associated with bottom trawling are

ercely contested, there is relative consensus (across

academia, civil society, sheries managers, and the shing

industry) that it is unique among shing practices in terms

of its environmental impacts. Bottom trawling is the most

widespread anthropogenic source of physical disturbance

to the seabed.vi In surveys of the shing industry, NGOs,

academia, and sheries managers, bottom trawl gears rank

highest among all shing gears in terms of their environmental

impacts (see Section 3: State of the evidence: environmental

impacts for a more in-depth discussion of this point).vii Yet

everything from its spatial footprint to the specic, local

character of its historical and current impacts has created

entrenched polarization. While sheries managers generally

focus on aligning bottom trawling with the standards applied

to all sheries, civil society organizations tend to advocate for a

more “gear-specic” approach of measures that apply solely to

bottom trawling, driven by its cumulative environmental, social

and climate impacts. Reconciling such fundamental divisions

is key to ensuring global progress in securing sustainable and

equitable sheries.

Bottom trawling presents unique and critical global

challenges to the environmental, social, and climate goals for

sheries. All shing gear types should be considered subject to

the SDGs, especially Target 14.4 relating to ending “overshing”

and “illegal, unreported and unregulated shing.” However,

bottom trawl sheries represent unique additional challenges

for the global goals and other international frameworks and

standards, particularly in ensuring international progress

in tackling “destructive shing practices” (also enshrined in

SDG14, leveraging off the UN Food & Agriculture Organization’s

Code of Conduct for Responsible Fisheries and other related

frameworks such as UN General Assembly resolution 59/25 on

high seas sheries).

This report assesses the current state of global evidence

around the status, extent and impacts of bottom trawling.

The authors believe that the acceleration of environmental

and social justice concerns in sheries in recent years

makes it a ripe time to revisit our understanding of the role of

bottom trawl sheries in achieving a sustainable planet and

a thriving society.vii Finding lasting solutions to the unique

challenges posed by bottom trawling is fundamental to the

growing international focus on the role of a healthy seabed in

maintaining a livable planet, which includes concerns about

deep-sea mining and the emerging evidence of seabed carbon

loss.ix,x Other topical political commitments include preserving

seaoor integrity (e.g., in the new EU Biodiversity Strategy), a

proposed moratorium on deep-sea mining, and more broadly

for industries to go beyond “do no harm” principles and be

active “contributors to an overall nature positive future” (e.g.,

in the UN Convention on Biological Diversity’s Post-2020

Draft Global Biodiversity Framework).xi,xii Equally, increasing

recognition that there are deep, regionally-specic social

inequalities in how sheries are managed requires a particularly

precautionary approach to bottom trawl sheries in areas of

minimal marine governance, transboundary exploitation and

contested shery access.xiii

To conclude the report, the authors propose a broad

framework of high-level recommendations to “TRANSFORM”

the status quo around bottom trawl sheries. The authors

hope to inspire constructive, inclusive, and meaningful action to

reduce the well-evidenced negative impacts of these sheries

and accelerate progress towards a healthy and just society, a

thriving ocean, and a livable planet.

New perspectives on an old shing practice: Scale, context and impacts of bottom trawling10

The Positive Disruption

Paradigm

Denitions and

historical context

New perspectives on an old shing practice: Scale, context and impacts of bottom trawling 11

Denitions and key terms

Bottom trawling is a widespread shing practice that involves

dragging a weighted net or rigid structure from a shing

vessel along the seaoor. The practice is used to catch

bottom-dwelling sh (cod-like sh and atsh), mollusks,

swimming crustaceans (shrimp/prawn), or non-specic

(mixed) demersal species. The term “bottom trawling” is often

conated with the word “trawling” which refers to both bottom

trawling and pelagic trawling (the towing of a net through the

water column).3 This report focuses on the practice of bottom

trawling, but calls out some instances where evidence or

impacts are conated.

The ecology of target species, especially their habitat

preferences, drives patterns of bottom trawling exploitation.

The extent to which target species are benthic (i.e., atsh

and shellsh that live and feed only on the seabed substrate),

benthopelagic (i.e., groundsh that live and feed close to, but

not always on, the seabed substrate) or infaunal (i.e., some

shrimp species that form burrows in the seabed) inuences

the design and physical properties of the gears and vessels

needed to catch them. The nature of these species’ preferential

substrate (i.e., from hard to soft substrate; from complex, multi-

dimensional seabed structures to simple, high-energy plains;

from shallow to deep waters) also determines how, where and

what forms of bottom trawling take place on the global seabed.

A diverse array of distinct shing gears can be used in

bottom trawling. The UN Food and Agriculture Organization

(FAO) denes a bottom trawl as “a cone-shaped net towed on

the seabed and designed to catch sh living on or near the

seabed.”xiv FAO lists six specic gears under this category in

its global classication of shing gears, principally separated

by the technology used to keep the trawl net open (either

“beams” or “otter boards”) or the number of trawl nets

deployed (single, twin/pair or multiple).xv An additional two

“towed demersal gears” (gears that are also intended for use

on the seaoor and are towed from a vessel but have different

properties to bottom trawl gear e.g., dredges) are also relevant

to this report (see Table 2).

3 Midwater (or pelagic) trawling – a practice that involves towing a trawl net through the water

column to target pelagic species – is not within the scope of, and should not be confused with,

bottom trawling.

Distinguishing between gears is important as their typical

conguration, use, and deployment are highly distinctive –

and this inuences their potential environmental impacts.

Some towed demersal gears are designed to penetrate the

seabed (e.g., the row of metal “teeth” on a scallop dredge)

while others are designed only to transit along it. In some

cases, the entirety of the catching device contacts the seabed

whereas in others it is only the main, lower part of the net (e.g.,

the footrope of a atsh pair trawl). While all towed demersal

gears should be considered to exert some inherent level of

pressure on the seabed, impacts associated with bottom

trawling sheries are not uniform in their character, scale, or

consequences. Bottom trawls (beam and otter trawls) involve

less penetration of the seabed than the use of dredges, and

therefore cause less overall depletion of biomass per single

trawl pass (6-14 percent for bottom trawls vs. 20-41 percent for

dredges).xvi Although bottom trawls have less impact at a local

level, their use and spatial footprint is far more widespread

than dredges, and they are responsible for 26 percent of all

seafood catch as compared to <1 percent for dredges.4 For the

remainder of this report the term “bottom trawl” applies only to

bottom trawl gears, and not dredges.

The range of bottom trawl gear types and target species

have led to such sheries emerging in diverse national and

international jurisdictions (which in turn inuences their

potential social impacts). Where bottom trawl sheries take

place (i.e., inshore or offshore waters; temperate or tropical

zones) inuences the scale of the eets and the sizes of

the vessels needed to effectively deploy these gears. These

parameters in turn inuence the magnitude of investment

needed to undertake extraction of specic bottom-trawled

commodities. Fisheries closer to shore tend to be operated

by more numerous, smaller vessels and sheries offshore

by fewer, larger vessels, although this distinction is not

consistent. A bottom trawl shery can be anything from the

six to seven vessels of various countries targeting orange

roughy on the high seas off southwest Africa (all vessels 80

m or longer), to the more than 1,000 “baby” inshore shrimp/

nsh trawlers in Cambodia, all below 12 m, working in a very

small shelf area.xvii,xviii

Fundamentally, the most common property of all bottom

trawling practices is the requirement to make sustained

contact with the seabed. Differences of scale, impact,

controversy, and level of management arise when considering

target species and where they live, the specic technologies

most appropriate to catch those species, and the social and

economic conditions surrounding the location where trawling

is taking place.

4 This number includes catch in EEZs and catch on the high seas. Source: Pauly D., Zeller D.,

Palomares M.L.D. (editors). 2020. Sea Around Us Concepts, Design and Data, seaaroundus.org.

2. Denitions and historical context

This section denes what bottom trawling is

and discusses its various forms. It also provides

historical context for the development and extent of

bottom trawl sheries. It concludes by considering

key debates about whether bottom trawling is an

“inherently destructive” practice and denitionally

“industrial” as a shing gear.

New perspectives on an old shing practice: Scale, context and impacts of bottom trawling12

Historical context: the emergence and growth

of bottom trawling

Towing or dragging demersal gears along the seabed has

happened, and been controversial, for at least 600 years of

human history. The earliest known references to the shing

practice of bottom trawling come from the 13th and 14th century

United Kingdom, the 16th century Netherlands, 17th century

Japan and 18th century France.xxi,xxii In most of these cases, the

references are from petitions to decision-makers to restrict

the use of these proto-trawl sheries – known variously in

northwest Europe as “wondyrchroum” and “wonderkuil,” terms

roughly translating as “marvelous shing trawl” – citing as their

rationale the loss of juvenile sh, the destruction of benthic

habitat, and the outcompeting of existing methods.xxiii

Temperate water bottom trawl sheries became

industrialized rst, prior to the 20th century. From the 1850s

onwards, driven by the industrial revolution in Europe and

North America, bottom trawling vessels were designed

for industrial operation. In the Northeast Atlantic the

introduction of steam-powered hauling aboard bottom trawl

vessels in the 1870s, and then steam-powered engines

and otter boards in the 1880s, began a 140-year process of

rapidly increasing the power to catch more fish per unit of

effort.xxiv Steam-powered trawling reached the USA by 1906

and began appearing throughout the early 1900s in, for

example, New Zealand, Chile, and South Africa.xxv, xxvi As with

all fishing activity, the two World Wars affected this growth,

but 1950s post-war innovations such as double-beam trawls

and diesel-powered engines – as well as the development of

export markets for key trawled commodities such as flatfish

– cemented this new global industry.xxvii These innovations

contributed to exponential growth in global catch across all

fishing methods from 1950 to 1970.xxviii

Tropical water bottom trawl fisheries emerged later, as

the technology was introduced in these regions in the

early 20th century. With some exceptions, bottom trawling

fisheries in the tropics were more recently developed than

Table 2 Bottom trawling gears and related towed demersal shing gears

Bottom trawling gearsxix, xx

FAO gear

category

National-scale environmental impact

rankings by gear type1

Global-scale environmental impact rankings by gear type2

Habitat impact Bycatch Fuel use intensity Habitat impact Bycatch

Trawl - bottom

Gillnet - bottom

Dredge

Pots & traps

Gillnet - midwater

Longline - bottom

Longline - pelagic

Trawl - midwater

Purse seine

Hook and line

References U.S.: Chuenpagdee et al., 2003

Canada: Fuller et al., 2008

United Kingdom: MMO, 2014

Parker and Tyedmers,

2015

Grieve et al., 2014 Wallace et al., 2013;

Lewison et al., 2014;

Oliver et al., 2015;

Gilman et al., 2020

Legend:

Methods:

1. Authors identied three studies in the U.S., Canada, and the U.K. that used a paired comparison analysis to directly compare shing gear types against each

other. Authors summed impact scores from each of the papers for all habitat feature interactions and bycatch species interactions by gear type, resulting in

mean habitat and bycatch impact scores across the three papers. Gear types that were not comparable across studies were removed. Absolute scores were

then converted into relative rankings for the remaining gear types. Relative rankings were converted into High, Medium, and Low terciles.

2. For each study, the authors ranked all cited gears based on their study-specic score. Gear types that were not comparable across studies were removed.

Study-specic ranks were then converted to relative ranks. Bycatch rank references studies across multiple species type (marine mammals, sharks, sea,

turtles, and non-specic discards). Ranks were averaged across the four studies, and then an overall relative rank was created. Impact scores were then

converted into High, Medium, and Low terciles. Where one of the gear/gear categories was represented by multiple gears in a detailed study, the authors

took the highest applicable rank.

Not all bottom trawling is the same in terms of its

environmental impacts. Impacts will vary depending on

the design of the gear and its operation, the frequency and

intensity of bottom trawling, the susceptibilities of the affected

ecosystem and species to trawling (mortality) and their ability

to recover (life history).c For example, hydraulic dredges cause

the greatest depletion of seabed biomass (sponges, soft

corals, macrofauna) from a single trawl pass (the duration and

distance covered by a trawl, also called “area swept”), followed

by towed dredges, beam trawls, and otter trawls.ci

The ability of bottom trawling and other towed demersal

gears to affect all three variables of interest to marine

biodiversity suggests that it is unique among shing gears.

However, singling out particular shing gears and their inherent

environmental properties can risk obscuring the importance

of context and the distinction between responsible and

irresponsible use. Critics of these kinds of gear comparisons

promote the implicit notion of “shing gear neutrality,” perhaps

best typied by the Marine Stewardship Council’s assertion

that “any shing will have an impact on the environment, but

its relative impact depends on a range of factors.”cii Bottom

trawling is often the implied focus of this concept. However,

the ndings presented in Table 5 above suggest that bottom

trawling is in fact different from other gear types, in that its

aggregate impact – as assessed by academics, the seafood

industry, sheries managers, and NGOs in paired comparison

studies – is highest across nearly every factor of concern

for marine biodiversity, and these trends become only more

apparent in global meta-analyses.

High Medium Low N/A

3. State of the evidence: environmental impacts

New perspectives on an old shing practice: Scale, context and impacts of bottom trawling18

How do we measure and manage seabed habitats that have different

characteristics and different histories of bottom trawling?

The emergence of bottom trawling in different parts of the world at different times means that some bottom trawl

sheries are relatively recent (i.e., multi-decadal) and some are extremely well established (i.e., multi-century) and that a

wide variety of seabed types are impacted by the practice. Meaningful baseline data on the ecological characteristics of

seabed habitats and demersal communities pre-bottom trawling are rare, which makes the process of dening impacts

(and appropriate parameters for recovery) both complex and contentious, particularly given that the “rst pass” of a

towed demersal gear may cause the most change.ciii,civ

Certain seabed habitats are of greater concern than others in relation to bottom trawl impacts. Slow-growing, coralline

communities in remote, deep areas are demonstrably less resilient to disturbance than high-energy areas of naturally

mobile sediment, with instances in which the former show no signs of recovery 15 years after initial trawl disturbance

and in which the latter can return to pre-trawl impact state within a year.cv A weakness of some bottom trawl seabed

impact studies showing relatively short recovery timeframes is their failure to account for the serial, sometimes multi-

century level of seabed contact that may have preceded the baseline year of such studies.cvi

The question of what it means for a seabed habitat to be “pristine,” “recovered” or in “favorable condition” is vital to

bottom trawling policy formulation, standard-setting and management. The most relevant policy concepts are those of

“avoiding signicant adverse impact” or “serious irreversible harm,” that are respectively applied to bottom trawl sheries

taking place in international waters or seeking Marine Stewardship Council certication. In order to be compliant with

either of these frameworks, sheries managers and bottom trawl operators must demonstrate that their activities

fall within the limits of acceptable impact (i.e., how much of a given habitat can be trawled) and acceptable recovery

timeframes. It is notable that i) neither of these two concepts are applied consistently in national or nearshore waters

(although some MSC-certied bottom trawl sheries operate in these waters); and ii) both concepts are based on “do no

harm” principles rather than aligning with emerging calls for any use of the environment to make an active contribution

to planetary health.cvii,cviii

3. State of the evidence: environmental impacts

New perspectives on an old shing practice: Scale, context and impacts of bottom trawling 19

The Positive Disruption

Paradigm

State of the evidence:

climate impacts

New perspectives on an old shing practice: Scale, context and impacts of bottom trawling20

Bottom trawling is attracting increasing attention for its

global impact on greenhouse gas emissions. The impact

of bottom trawling on climate change can be broken down

into two primary mechanisms: the relatively high fuel use of

trawling vessels and the disturbance of carbon-containing

sediments on the seaoor.

Fuel use

Fisheries consume about 40 billion liters of fuel annually,

generating 179 million tonnes of CO2-eq GHG emissions

(about 4 percent of global food production emissions).cix Of

the major gear types used in global sheries, bottom trawling

has the highest emissions from fuel use. Seafood is often

credited for being a “more sustainable” dietary choice with

regards to climate change because the average GHG emissions

per gram of protein consumed are less than 1/10 those of beef.cx

However, GHG emissions vary signicantly by gear type, and

sh caught by bottom trawling can rank among the most GHG-

intensive foods due to the fuel use requirements of dragging a

heavy net across the seaoor.

A 2017 study showed that bottom-trawl sheries emit almost

three (2.8) times more greenhouse gases than non-trawling

sheries.cxi This estimate gives sh caught by bottom trawling

a higher GHG footprint than most meat, except for lamb and

beef. While the carbon footprint of land-based protein sources

includes land-use change and feed emissions, bottom-trawled

sh account for more emissions than pork and poultry through

associated fuel use alone – without including broader life-cycle

considerations (see Figure 1). Within bottom trawl sheries,

the catch of small crustaceans (shrimp) and non-schooling

sh (atsh) have comparatively high carbon emissions

compared to catching species that form schools (e.g., cod and

cod-like species).

Trawling emissions from fuel use can be mitigated by

switching to different gear types. Studies have shown that

fuel use can be decreased by 4x per kilo of Norway lobster,

15x per kilo of Danish atsh, and 4x per kilo of Swedish

cod when switching to creel, Danish seine, and gillnet gears,

respectively.cxiii, cxiv, cxv

Sediment disturbance

Bottom trawling may also generate up to 1.47 Gt CO2-eq

annually by disturbing seabed sediments, according to

emerging research. Sala et al. (2021) attempted for the

rst time to quantify the disturbance of carbon-containing

sediments from bottom trawling and the subsequent release

of that carbon back into the water column and atmosphere.cxvi

4,000

kg CO2e t–1 edible weight

Risk index

8,000 12,000 16,000

50% 80% 95%

Gear:

Figure 1

Median

Confidence:

Midwater trawls

Bottom trawls Traps and lift nets

Demersal species (NE Atl)

Demersal species

(NE Atl.)

Pelagic species (NE Atl)

Crustaceans (NE Atl)

Lobsters (C Am SSF)

Gillnets and entangling nets

Seafood caught by bottom trawls generates among the highest carbon

emissions per tonne of edible weight, along with crustaceans caught through

traps and lift nets. Data represent fisheries in Europe (NE Atlantic) and Central

America (C Am SSF) by gear type. The risk index is the sum of the number of

marine mammals at risk from bycatch.

4,000

kg CO2e t–1 edible weight

Risk index

8,000 12,000 16,000

50% 80% 95%

Gear:

Figure 1

Median

Confidence:

Midwater trawls

Bottom trawls

Traps and lift nets

Demersal species (NE Atl)

Demersal species

(NE Atl.)

Pelagic species (NE Atl)

Crustaceans (NE Atl)

Lobsters (C Am SSF)

Gillnets and entangling nets

Seafood caught by bottom trawls generates among the highest carbon

emissions per tonne of edible weight, along with crustaceans caught through

traps and lift nets. Data represent fisheries in Europe (NE Atlantic) and Central

America (C Am SSF) by gear type. The risk index is the sum of the number of

marine mammals at risk from bycatch.

4,000

kg CO2e t–1 edible weight

Risk index

8,000 12,000 16,000

50% 80% 95%

Gear:

Figure 1

Median

Confidence:

Midwater trawls

Bottom trawls

Traps and lift nets

Demersal species (NE Atl)

Demersal species

(NE Atl.)

Pelagic species (NE Atl)

Crustaceans (NE Atl)

Lobsters (C Am SSF)

Gillnets and entangling nets

Seafood caught by bottom trawls generates among the highest carbon

emissions per tonne of edible weight, along with crustaceans caught through

traps and lift nets. Data represent fisheries in Europe (NE Atlantic) and Central

America (C Am SSF) by gear type. The risk index is the sum of the number of

marine mammals at risk from bycatch.

4,000

kg CO2e t–1 edible weight

Risk index

8,000 12,000 16,000

50% 80% 95%

Gear:

Figure 1

Median

Confidence:

Midwater trawls

Bottom trawls Traps and lift nets

Demersal species (NE Atl)

Demersal species

(NE Atl.)

Pelagic species (NE Atl)

Crustaceans (NE Atl)

Lobsters (C Am SSF)

Gillnets and entangling nets

Seafood caught by bottom trawls generates among the highest carbon

emissions per tonne of edible weight, along with crustaceans caught through

traps and lift nets. Data represent fisheries in Europe (NE Atlantic) and Central

America (C Am SSF) by gear type. The risk index is the sum of the number of

marine mammals at risk from bycatch.

4. State of the evidence: climate impacts

Seafood caught by bottom trawls generates among the highest carbon emissions per tonne of edible weight, along

with crustaceans caught through traps and lift nets. Data represent sheries in Europe (NE Atlantic) and Central America

(C Am SSF) by gear type. The risk index is the sum of the number of marine mammals at risk from bycatch.cxi

Figure 1 GHG emissions from seafood, by gear type, compared to marine mammal risk

This section discusses the contributions of bottom

trawling to climate change. It examines the well-

established evidence base on the fuel intensity

of the practice as well as emerging research on

the role of bottom trawling in disturbing marine

sediments that store carbon.

New perspectives on an old shing practice: Scale, context and impacts of bottom trawling 21

Using a global average of carbon accumulation and

sedimentation rates combined with automatic identication

system (AIS) data from bottom trawling vessels, the authors

estimated that bottom trawling could release between 0.6

and 1.5 Gt CO2e a year, roughly equivalent to the entire global

aviation industry. Though these estimates are an emerging

area of research, countries with high estimated emissions

from bottom trawling are predominantly in Western Europe,

due to the intensity of trawling in those regions as recorded

by Global Fishing Watch data (see Figure 2). China appears

to be the leading emitter of CO2 into the atmosphere through

bottom trawling activities, due to both high trawling intensity

and total trawling effort. Since AIS data to track vessel trac

is limited in Southeast Asia, South Asia, and West Africa,

GHG emissions from bottom trawling in those regions may

be underestimated. This study builds on previous work to

produce 1-km resolution estimates of marine sedimentary

carbon stocks globally.cxvii

Additional research is needed to rene these estimates.

Future work should focus on building a spatially explicit map

of global carbon accumulation and sedimentation (especially

in heavily bottom-trawled areas) and attempting to reduce the

large uncertainty over the proportion of carbon that is released

back into the atmosphere. Initial research mapping organic

carbon densities and accumulation rates in the Norwegian

Trough and Skagerrak found that sediment stocks vary

spatially in those regions, indicating that restricting bottom

trawling may have different effects on carbon emissions

depending on locality.cxviii Rening carbon stock estimates

and resuspension rates in areas where bottom trawling is

occurring will be important to ensure that ocean areas are

being managed both to protect biodiversity and to minimize

GHG emissions.

Figure 2 Estimated GHG emissions from bottom

trawling (Gephart et al., 2021)

Preliminary estimates suggest that the emissions from bottom

trawling in China are over an order of magnitude greater than any

other country. Emissions are otherwise concentrated in Europe,

where trawling intensity is high.cxix

Russia Italy United Kingdom Denmark

France Netherlands Norway Croatia Spain

Figure 2

769.3

Mt CO2 yr–1

China

84.7 66.8

47.7 39.7

31.1

26.1 23.2

22.830.2

4. State of the evidence: climate impacts

New perspectives on an old shing practice: Scale, context and impacts of bottom trawling22

The Positive Disruption

Paradigm

State of the evidence:

socio-economic impacts

New perspectives on an old shing practice: Scale, context and impacts of bottom trawling 23

Documented socio-economic impacts

associated with bottom trawling

Conceptualizing the socio-economic impacts of bottom

trawling is more nuanced and complex than documenting

its environmental impacts. Conservation practitioners and

scientists have historically failed to value and study both the

natural and social dimensions of environmental problems.cxx

The lack of understanding about the social dimensions of

conservation hinders the ability to design solutions that can

improve environmental and social outcomes.cxxi This shortcoming

manifests through the poor conceptualization of bottom trawling’s

socio-economic impacts in the academic literature.

Formal documentation of bottom trawling’s socio-economic

impacts is limited. The authors conducted a global literature

review and found 31 papers that explicitly discuss trawling’s

socio-economic impacts, compared to the many more papers

that explore its environmental impacts.7 For example, a recent

meta-analysis on bottom trawling’s footprint cited almost

double the number of academic papers.cxxii Interpretation and

understanding of socio-economic impacts across non-English

speaking regions may be rudimentary since this review only

considered English language literature. Regions in data-poor

and under-researched parts of the world (such as low- and

middle-income countries) are likely inadequately represented.

Other socio-economic dynamics, including inequitable

benet-sharing between seafood corporations and coastal

communities, might be uncovered if additional sources of

information were included in this analysis.8

The tendency to conate bottom trawling with midwater

trawling, or more generally industrial shing, makes it dicult

to determine the unique socio-economic impacts of each

shing gear. The available socio-economic literature rarely

7 In April 2021 CEA Consulting conducted a review of scientic literature focused on the social

impacts associated specically with bottom trawl sheries. The scope included both bottom and

midwater trawling since most of the literature described trawling in generalized terms. A total of

31 papers, published since 2000, were reviewed for content describing the socio-economic impli-

cations of trawling on coastal and shing communities. Most of the literature focused on South

Asia followed by East and West Africa, Latin America, and the Mediterranean, with less coverage

on Western Europe, Southeast Asia, and South Africa.

8 In addition to the ndings from the literature review, expert interviews highlighted anecdotal obser-

vations and eyewitness testimony of socio-economic impacts related to bottom trawling. Experts

suggest that bottom trawling is often a taboo topic given the nuanced role it plays in shaping coast-

al communities. For example, in India trawlers (bottom, pelagic, and midwater) are often owned and

operated by poor shers, resulting in a general social opposition to complete bottom trawling bans.

disaggregates by gear type, in contrast to environmental

impact studies. While many of the impacts found through

this analysis are not unique to bottom trawling, they have

all been documented with respect to bottom trawling and

therefore merit consideration. The limitations of the current

evidence base for socio-economic impacts requires a nuanced

discussion of bottom trawling’s outcomes.

Five broad themes for the socio-economic impacts of

bottom trawling emerged from the authors’ literature review:

economic impacts, violence and conict, food security, labor

and human rights, and occupational health and safety.cxxiii

Documented socio-economic impacts apply to those affected

by bottom trawling, often small-scale shers, as well as to

those within the bottom trawling sector.

1. Economic impacts include impacts on jobs, landings and

food supply, public revenues from access agreements

and license fees, and subsidies. Impacts documented can

be both positive and negative, which may help to explain

why bottom trawling is both widespread and controversial.

• Jobs and economic opportunities. Bottom trawling may

increase labor productivity in the sector if it replaces more

economically inecient forms of shing. If workers can

move to higher quality jobs, then the total effect could be

positive. However, workers cannot always transition to other

jobs, particularly in coastal countries with fewer alternatives,

which may result ultimately in job losses overall.9 For

example, in the case of Colombia bottom trawling has

been documented to offer shers with limited income

opportunities the chance to increase their incomes due to

the low investment and maintenance costs, low operational

risks, high value of target species, and high protability of

the sector, when compared to alternatives.cxxiv

• Foreign shing access agreements. Coastal countries

often trade shing access agreements with foreign

countries to prot from their sh resources.cxxv Foreign

access agreements with distant water bottom trawl

eets often result in sub-optimal economic outcomes

for host countries, including lost economic rents,

high opportunity costs, and proportionally little value

remaining in-country. West Africa is a prime example

of the economic impact that foreign bottom trawlers

have on local shing communities. In Sierra Leone these

agreements add up to 2-3 percent of estimated total

resource rents from shing, or about $2 million annually.cxxvi

Many countries with large shery resources are trading

off cash in hand today to allow bottom trawling. The

economic benet from this trade often stays within

central governments and is not reinvested into the long-

term livelihoods and economic growth of the coastal

communities directly affected by the agreements.

9 Personal communication with John Virdin.

5. State of the evidence: socio-economic impacts

This section shares the ndings of a global academic

literature review conducted by the report authors to

identify and categorize the kinds of social impacts

associated with bottom trawling. It also presents

an in-depth case study of bottom trawling in West

Africa, and the socio-economic implications of the

practice there.

New perspectives on an old shing practice: Scale, context and impacts of bottom trawling24

• Subsidies. Government subsidies exist across multiple

gear types, but deep-sea bottom trawl sheries are

major beneciaries.cxxvii Bottom trawling remains

protable across the high seas, even though it is a fuel-

intensive shing method, because of subsidies. Without

government subsidies, high-seas bottom trawling would

be largely unprotable.cxxviii Experts suggest that bottom

trawlers shing in the high seas receive $152 million per

year in the form of subsidies, representing 25 percent of

the eet’s total landed value.cxxix

2. Violence and conict often characterize the relationship

between small-scale shers and industrial bottom trawlers,

involving physical conict, shing gear loss and damage,

and political confrontation. The long history of violence and

conict between Sri Lankan and Indian shers and bottom

trawlers is particularly well documented, demonstrating

entrenched animosity between bottom trawlers and

artisanal shers of both countries.cxxx,cxxxi,cxxxii,cxxxiii,cxxxiv,cxxxv

Illegal cross-border bottom trawling has often resulted in

artisanal shers facing irreparable damage to their nets.

cxxxvi The heightened tension has led to increased patrolling

and arrests of shers of both countries.cxxxvii

3. Food security implications from bottom trawlers depend

on what is caught and who can consume that catch.

• Negative outcomes. In many coastal sheries

throughout the tropics, bottom trawlers often out-

compete local small-scale shers and deplete local

resources historically caught by small-scale shers

or consumed by local communities.cxxxviii,cxxxix These

impacts have resulted in reduced food, lower incomes,

and forced migration in countries such as India, where

90 percent of small-scale shers live below the poverty

line and sh catches have decreased at alarming rates

in recent years.cxl

• Positive outcomes. Bottom trawling can provide cheap

sh for human consumption. The bottom trawl sheries

in Southeast Asia provide food for millions of people

in coastal communities as well as feed for the region’s

growing aquaculture sector, which is largely consumed

by low and middle income consumers in Asia.cxli,cxlii

Some experts suggest that global demand for sh

will double by 2050, with urbanization as an important

driver.cxliii While current sh consumption per capita in

Asia, Europe and Oceania surpasses the global average,

consumption across Africa and South America is well

below it.cxliv Demersal species are most in demand in

Europe, North America and Oceania.cxlv

• Overall outcomes. Bottom trawling is occurring in

countries that are highly dependent on marine resources

for food security, particularly in West Africa and

Southeast Asia (see Figure 3).cxlvi Given the complicated

interplay between these social, environmental, and

economic systems, efforts to constrain bottom trawling

Figure 3

Degree of human dependence on marine ecosystems for nutrition

LowHigh

No data

Countries with the highest nutritional dependence on seafood, in order, include the Maldives, Kiribati, the Solomon

Islands, Sierra Leone, Sri Lanka, Palau, Ghana, Tavalu, Nauru, Cote D’Ivoire, Indonesia, and Senegal.cxlvii

5. State of the evidence: socio-economic impacts

Figure 3 Degree of human dependence on marine ecosystems for nutrition (Selig et al., 2019)

New perspectives on an old shing practice: Scale, context and impacts of bottom trawling 25

in these places may give rise to concerns about

unintended consequences for human well-being.

4. Human rights abuses such as unlawful arrest, torture,

and even murder connected to bottom trawling have

been documented, particularly in South Asia. Human

rights violations affecting Indian and Sri Lankan shers

have been documented and debated in domestic and

international media.cxlviii The use of social media platforms

has facilitated the swift sharing of videos and cases

depicting abuses, and this has increased public attention

on the conict over resources and the right to sh.cxlix

5. Occupational health and safety may be an

underappreciated problem for trawling eets, although

evidence of impacts by gear type is very limited.

Documented occupational health and safety impacts

were associated with trawling more generally and did

not explicitly refer to bottom trawling.cl However, these

impacts merit discussion given the similarities between

the shing methods.The International Labour Organization

(ILO) identied shing as among the most dangerous

occupations.cli In Norway, commercial shing is recognized

as the occupation with the most fatal and nonfatal

accidents, with the trawler eet holding the highest injury

rates in the shing sector.clii Trawling-related injuries

accounted for an estimated 37 percent of all reported

injuries across the entire Norwegian shing eet.cliii

More research is needed to differentiate risks specically

associated with bottom trawling.

The socio-economic impacts of bottom trawling may vary

based on ecological conditions, with a distinct difference

between temperate and tropical sheries. Fish that live in

temperate waters have life histories that involve the open

ocean and deep waters, which generally allows for deep-

water bottom trawl sheries. As a result, there can be a

natural spatial separation between bottom trawlers targeting

deep-water species, such as orange roughy, grenadiers, and

toothshes, and other shing vessels that target shallower or

inshore waters. Tropical waters tend to be more productive

inshore than offshore, so more of the shing occurs closer

to shore. As a result, there is a higher likelihood of spatial

overlap and conict between sheries, especially with small-

scale shers. Most of the world’s marine small-scale shers

sh in tropical waters near the shore, where the majority of

bottom trawling is taking place.cliv Small-scale shers are

particularly vulnerable and often marginalized, forced to endure

the consequences of ineffective shing regulations, market

inequity, and environmental shocks.clv For these reasons, some

governments, particularly in Africa, have pursued the creation

of inshore exclusion zones (IEZs) to restrict bottom trawling in

coastal waters.clvi This human-centered approach is designed

to protect artisanal sheries from the socio-economic impacts

of bottom trawling and other industrial forms of shing –

enforcement, however, is critical.clvii

Inshore exclusion zones as a tool to

support small-scale sheries

Inshore exclusion zones (IEZs) are a spatial management

tool used by governments to address the socio-economic

impacts of industrial shing. IEZs are found within a

country’s jurisdiction, typically within territorial waters (12

nautical miles from shore), and are usually areas reserved

for small-scale shing craft where industrial shing may

be prohibited. Because bottom trawling is nearly always

categorized as industrial shing, an industrial ban also

serves as an implicit ban on bottom trawling. However,

some IEZs, such as Cambodia’s, explicitly target bottom

trawling in their sheries laws.clviii African governments

in particular have implemented IEZs as a result of the

conicts between foreign trawlers and small-scale shers

in the region. Industrial eets have been documented

within African inshore areas reserved for small-scale

sheries, resulting in fatal collisions, increased competition,

and conict over shing access.clix In some cases, IEZs

have demonstrated progress toward combating illegal

shing and protecting local shers. In 2010 the Liberian

government introduced a six-nautical mile IEZ protecting

the inshore artisanal shery, which supports the livelihoods

of an estimated 33,000 people.clx The decrease in illegal

shing and increase in artisanal catch in Liberia is attributed

to the implementation of the IEZ.clxi This in turn has also

led to a reduction in conict with industrial shing vessels

and an overall improvement in artisanal livelihoods.clxii

Similar to other spatial management measures, IEZs are

often a result of technocratic processes and in some cases

receive technical assistance from FAO. The success of

IEZs may depend on proper enforcement. Illegal trawler

encroachment of IEZs in Sierra Leone has resulted in

conict and violence, suggesting discrepancies in the

effectiveness of IEZs.clxiii The Illuminating Hidden Harvests

report, an upcoming FAO, WorldFish, and Duke University

study, will include an analysis on the extent of IEZ coverage

in 58 country case studies across the world, with insights

relevant for the connection of small-scale sheries to

bottom trawling.

5. State of the evidence: socio-economic impacts

New perspectives on an old shing practice: Scale, context and impacts of bottom trawling26

Case study examples highlight the connections between

bottom trawling and food security, erosion of cultural

practices, and loss of local livelihoods. Case studies from

Myanmar, Scotland and Peru demonstrate how bottom

trawling is part of a broader trend towards the capitalization

and commoditization of sheries that often favor corporate,

foreign, and urban interests at the expense of traditional

shers and local communities. These trends can play out

relatively quickly or over generations, and have not been

widely studied.

• In Myanmar, the increased global demand for shmeal

and sh oil has encouraged the development of a bottom

trawl “trash sh” shery.10 This dynamic is shifting seafood

out of the mouths of local consumers (who historically

consumed bycatch from the bottom trawl shery) and into

export-oriented supply chains for animal feed – all while

decimating local shery resources.clxiv

10 Trash sh is a misleading but widespread term used to describe unwanted species with

usually little to no market value for human consumption that are typically caught when shing

for more valuable, targeted species.

• In Scotland, an IEZ established in 1889 prohibited bottom

trawling within three miles from shore in order to protect

small-scale sher livelihoods. Nearly 100 years later, the

1984 repeal of that IEZ resulted in the collapse of inshore

sheries, conict between artisanal and industrial shers,

loss of economic opportunities for coastal communities,

and the loss of historical cultural practices such as

sherman’s dances.clxv,clxvi,clxvii,clxviii

• In Peru, the economic opportunities presented by bottom

trawling displaced traditional small-scale shing, with some

small-scale shers adopting bottom trawling to take advantage

of the greater economic stability and opportunity it provided in

comparison to traditional practices. A recent study documented

how small-scale shers that used trawl nets and purse seines

were the only small-scale shers who did not experience a

decline in annual income for the past seven decades, with most

other artisanal shers living in relative poverty.clxix

Figure 4

Type of interaction

Conflict over

ocean space

Competition

for fisheries

resources

Cooperation in

value chains

Incidents of violent and non-violent

conflict between fishers and vessels

Accidents involving SSF vessels

and loss of life for fishers

Damaged or lost SSF gear

Increased economic costs for SSF

Reduced food security for communities

Transshipment of trawl catch to SSF

vessels for sale

Type of impact on small-scale fisheries (SSFs)

Interactions and impacts between bottom

trawlers and SSFs in West Africa.

Figure 4 Interactions and impacts between bottom trawlers and SSFs in West Africa.

5. State of the evidence: socio-economic impacts

New perspectives on an old shing practice: Scale, context and impacts of bottom trawling 27

Deep dive into West Africa, a region

profoundly inuenced by trawling.10

Trawl vessels have dominated the large-scale sheries in West

Africa, a region where persistent and largely foreign trawling

has been relatively well documented.clxx The analysis of socio-

economic impacts across West Africa includes both bottom

trawl and midwater trawl sheries, since most of the literature

describes small-scale sheries interactions with trawl sheries

more generally. The conict between trawlers and small-scale

sheries is a key and dening feature of West African sheries.

Since the 1950s the region’s coastal waters have been shed

by foreign industrial trawl vessels, from Europe, Russia and

more recently China.clxxi There is a reinforcing feedback loop

with the ecosystem, where declining sh stocks are both an

outcome and a driver of the interaction between trawlers

and small-scale shers.clxxii Formal governance systems and

the capacity, or willingness, of governments to monitor and

enforce compliance with shing laws and regulations are also

often cited as drivers of this interaction.clxxiii

Three broad and mutually exclusive categories of interaction

between trawl sheries and small-scale sheries were

identied, with the rst two interactions described as key

characteristics of West African sheries.clxxiv

These three interactions are categorized as conicts over

ocean space, competition for sheries resources, and

cooperation in value chains.

1. One of the main interactions between trawl and SSF

vessels is conict over ocean space.clxxv Spatial overlap

is not necessarily static, which can heighten the risk of

conict as trawlers or SSF vessels follow each other to

shing grounds or shift shing areas due to environmental

and seasonal variations.

a. Incidents of violent and non-violent conict between

shers and vessels overlapping in operating space is quite

common. In Senegal, for example, SSF and trawl vessels

often sh alongside one another, resulting in physical

violence such as throwing bottles, rocks or ignited objects

from boat decks, spraying water at high pressure to damage

or tip a vessel, and threats and attacks involving weapons.clxxvi

There are also documented accidents involving vessels and

loss of life as a result of collisions with trawlers. More than

250 small-scale shers die every year in West Africa as a

result of collisions with trawlers, although this number may

be higher as accidents often go unreported.clxxvii In Senegal

alone, collisions with trawl vessels were the most common

cause, an estimated 30 percent, of SSF vessel accidents

between 2001 and 2006.clxxviii

b. Damaged or lost gear from interactions with trawl vessels

was frequently reported by small-scale shers, particularly

closer to shore or at night. In Sierra Leone, small-scale

shers in major landing sites reported damage to their nets

that in some cases was nancially crippling, claiming that

“every sherman in the community is now a debtor…if they

do not borrow, they cannot survive.”clxxix

c. Increased economic costs for small-scale shers have

also been documented. A recent study suggests that

the majority of shers in Sierra Leone believe that the

competition has reduced the availability of resources in

closer waters, forcing them to travel farther and incur

higher shing costs, such as for fuel.clxxx

2. While not perfectly interchangeable, the higher eciency

of trawl vessels can outcompete small-scale shers for

the same resources – and they often do in West Africa,

resulting in intense competition for sheries resources.

There are increased economic costs for small-scale

shers, similar to the impact from conict over ocean

space as previously stated. Additionally, there are negative

implications for community food security because of

reduced catches due to competition for sheries resources

with trawl vessels, though with relatively little analysis of the

magnitude of the impact. It is known that trawl operations

within nearshore waters legally reserved for small-scale

sheries have continuously “put a strain on food security.” clxxxi

3. Lastly, in some instances trawl vessels cooperate across

value chains with transshipment of trawl catch being sold

to small-scale shers. The saiko shery in Ghana is a clear

example of this cooperation, where trawling vessels sell

back trawled sh caught in the inshore zone to small-scale

shers who have legal rights to catch that sh. Ghana’s

small-scale shing sector, which employs about 80 percent

of the country’s shers and ensures livelihoods for more

than 2 million people, continues to decline and risks a

possible collapse.clxxxii An estimated 200 coastal villages

in Ghana depend on sheries as their primary source of

income.clxxxiii In 2017 around 80 saiko canoes landed over

55 percent of the total artisanal sector catch.clxxxiv This

cooperation is likely in response, at least partially, to the

effects of conict over ocean space and competition, and

can be seen as an adaptation by local shers to maintain

access to resources.

• 11

11 John Virdin and Dana Grieco from Duke University conducted a review of the scientic literature for the period

from January 1, 2000 to January 1, 2020. Search strings were developed from a review of key recent papers on West

Africa’s sheries as well as a review of their references. These search strings were used on March 17, 2021 in the

following databases: Web of Science, Scopus and the Earth Atmospheric and Aquatic Sciences (EAAS) database,

returning 38 papers for review. The papers retained were reviewed for content describing interactions between the

trawl sheries and small-scale sheries in West Africa. Following an inductive approach, the interactions between

trawl and small-scale sheries were identied and categorized based on open coding, together with the types of

impacts on small-scale sheries from each category. Finally, with categories of interactions identied, and their

associated impacts on small-scale sheries, the information relevant to each was synthesized.

5. State of the evidence: socio-economic impacts

New perspectives on an old shing practice: Scale, context and impacts of bottom trawling28

The Positive Disruption

Paradigm

Global extent

New perspectives on an old shing practice: Scale, context and impacts of bottom trawling 29

Contribution of bottom trawling to global catch

According to reconstruction estimates from Sea Around Us

(SAU), bottom trawling represents 26 percent of the global

sheries catch within exclusive economic zones (EEZs) but

varies signicantly by country and region (see Figure 5).12

In 2016, the last year for which data is fully available, this equated

to 30.5 million tonnes of seafood caught by bottom trawls

within EEZs.13 Less than 1 percent of bottom trawling occurs

outside EEZs, amounting to about 0.2 million tonnes of catch in

2016. Bottom trawling catches saw a steep growth beginning

in the 1950s from less than 8 million tonnes/year to a peak

of 36.5 million tonnes in 1989, followed by a period of decline

and stabilization. In recent years, bottom trawling has pulled in

approximately the equivalent quantity of sh to all artisanal gears

combined, and nearly three times that of pelagic trawling gears.

12 Sea Around Us (SAU), a research initiative at the University of British Columbia, uses “reconstructed”

global catch data to combine ocially reported landings with comprehensive estimates of unreported

landings and discards. While the catch reconstructions have some uncertainty, this methodology led

to the most comprehensive database of global catch estimates in the world. The catches therein can

be disaggregated by gear type and locality to estimate trends in bottom trawl catch. The report’s au-

thors used SAU data for this study because catch can serve as a proxy for shing effort. Additionally,

no other dataset exists that allows comparisons at the global level. Efforts to describe bottom trawling

effort in greater detail have mostly focused on specic seabed areas, such as Amoroso et al. (2018).

Other datasets, such as those provided by Global Fishing Watch, are currently constrained to where

automatic identication system (AIS) data is available. The period used for this analysis, 2007-2016,

represents the most recent decade for which full catch reconstruction data was available while this

report was being written; since the analyses reported herein were performed, the SAU data were

updated to 2018. These new data do not modify the trends and comparisons reported.

13 SAU data disaggregates catch by gear type. In the database “bottom trawl” refers to beam

and otter trawls. Seafood caught via dredge is not included in these estimates, as it accounts

for only 0.91 percent of all seafood caught in EEZs and the high seas in the latest year for

which there is complete data (2016).

Figure 5 Global marine sheries catch within EEZs

from 1950-2016, by gear type. Source: Sea Around Us (SAU)

Bottom trawling saw a steep growth beginning in the 1950s from less

than 8 million tonnes/year to a peak of 36.5 million tonnes in 1989,

followed by a period of decline and stabilization.clxxxv

Patterns showing stability in bottom trawl catch at the global

level obscure trends and impacts at the regional, national,

and sub-national level. Some areas have signicantly higher

or lower amounts of catch from bottom trawling than others,

and total catch is an imperfect proxy for environmental impact

because an overexploited shery can have low catch amounts

but involve a high effort (i.e., repeated bottom trawling of the

seabed) due to depleted local stocks.

The percentage of total catch from bottom trawling gears varies

signicantly by region. Oceania14 has the highest proportion of its

total catch from bottom trawling with 44 percent – almost twice

the global average. Within this region, New Zealand has a similar

quantity of bottom trawl catch to Australia despite only having

some 20 percent of its population size, pulling approximately 53

percent of its total catch through bottom trawling. In contrast,

only 4 percent of the total catch in South America comes from

bottom trawling due to the region’s focus on small pelagic sh like

anchoveta. In Africa, Asia, and North America, approximately 21-

29 percent of the total catch is caught via bottom trawling – this is

consistent with global averages and represents almost 24 million

tonnes of catch per year.

14 The authors assigned bottom trawling catch at the continent level based on EEZs. Countries with EEZs

spanning multiple continents were split proportionally so that catch occurring in the EEZs of particular

continents was properly attributed to that continent. For example, bottom trawl catch in Russia’s six EEZs

was assigned to either Arctic, Asian, or European catch based on the location of each EEZ.

1950 1960 1970 1980 1990 2000 2010

Global catch within EEZs (million tonnes)

100

120

140

Bottom trawl Pelagic trawl

Miscellaneous artisanal gear Miscellaneous industrial gear

Figure 5

Bottom trawling saw a steep growth beginning in the 1950s from

less than 8 million tonnes/year to a peak of 36.5 million tonnes in

1989, followed by a period of decline and stabilization.

1950 1960 1970 1980 1990 2000 2010

Global catch within EEZs (million tonnes)

100

120

140

Bottom trawl Pelagic trawl

Miscellaneous artisanal gear Miscellaneous industrial gear

Figure 5

Bottom trawling saw a steep growth beginning in the 1950s from

less than 8 million tonnes/year to a peak of 36.5 million tonnes in

1989, followed by a period of decline and stabilization.

6. Global extent

This section uses novel analysis of global catch

reconstructions provided by Sea Around Us, a research

initiative at the University of British Columbia, to

estimate the global extent of bottom trawling. It

presents historical trends by geography and gear

type and discusses limitations with these estimates.

It offers a discussion on the global distribution of

environmental impacts from bottom trawling and

concludes with a separate discussion of foreign shing

eets and their contribution to bottom trawling catches.

New perspectives on an old shing practice: Scale, context and impacts of bottom trawling30

6. Global extent

From 2007-2016, more than half of all bottom trawling catch

was caught in the EEZs of Asian countries (see Figure 6).

Bottom trawling peaked in Asia before the fall of the Soviet

Union at around 18 million tonnes/year in 1989, when a large-

scale switch from bottom trawl to pelagic trawl for Alaska

pollock in the Russian Far East and eet diversication in the

Barents Sea precipitated a global decrease in bottom trawl

catch.clxxxvi Since the gear transition, Russia’s total bottom

trawl catch has amounted to less than 1 million tonnes/year,

while dramatic increases in China and Vietnam have driven the

rise in bottom trawl catch in Asia back to 1989 levels. In most

other regions, bottom trawling is slightly declining or staying

constant (although individual countries may vary).

In Europe, bottom trawling as a percentage of overall catch has

decreased relative to pelagic trawling, which began taking over

a more signicant portion of the catch in the late 1990s.

Major bottom trawling regions overlap with areas of the world

where the majority of small-scale shing occurs. According to

the Hidden Harvest report, 97 percent of workers in commercial

capture sheries value chains are in developing countries,

predominantly Asia and Sub-Saharan Africa, of whom more

than 90 percent work in the small-scale sheries subsector.clxxxvii

These two regions also have the highest absolute amounts of

bottom trawling, which can create conict between industrial

and small-scale shers.

NORTH

AMERICA

SOUTH

AMERICA

EUROPE

AFRICA

ASIA

OCEANIA

Figure 6

Bottom trawl

Pelagic trawl

Miscellaneous artisanal gear

Miscellaneous industrial gear

1.62.1 4.5 1.5

3.01.2 9.7

0.2

1.22.3 4.6 2.5

3.44.5 2.8 2.0

15.9

16.8 Mt yr–1 16.7 5.1

0.2

0.4 0.3 0.02

NORTH

AMERICA

SOUTH

AMERICA

EUROPE

AFRICA

ASIA

OCEANIA

Figure 6

Bottom trawl

Pelagic trawl

Miscellaneous artisanal gear

Miscellaneous industrial gear

1.62.1 4.5 1.5

3.01.2 9.7

0.2

1.22.3 4.6 2.5

3.44.5 2.8 2.0

15.9

16.8 Mt yr–1 16.7 5.1

0.2

0.4 0.3 0.02

Figure 6 Global catch by gear type (within EEZs)

Asia contributes 60 percent of global bottom trawl catch, totaling approximately

14 million tonnes/year over the last decade of available data (2007-2016).clxxxviii

New perspectives on an old shing practice: Scale, context and impacts of bottom trawling 31

Major bottom trawling countries

At the sub-continent level, bottom trawling is concentrated in

East Asia, Southeast Asia, and West Africa. The top 10 bottom

trawling countries contribute 64 percent of the global bottom

trawling catch. Of these 10 countries, seven are in Asia: China,

Vietnam, Indonesia, India, Japan, South Korea, and Malaysia

(see Table 6). Given the outsize role of these countries, they

may be promising focal areas for efforts to minimize the

ecological and socio-economic impacts of bottom trawling.

Table 6 Top 10 bottom trawling countries by total catch

and percentage of global catch.clxxxix

Country Average annual bottom

trawl catch (2007-2016)

in million tonnes

Percentage of

global bottom

trawl catch

China 4.1 14.9

Vietnam* 2.3 8.3

Indonesia 2.2 8.1

India* 1.9 6.8

Morocco* 1.8 6.5

Japan 1.8 6.4

South Korea 1.1 4.1

United States 1.1 4.0

Argentina* 0.7 2.5

Malaysia 0.7 2.4

*Vietnam, India, Morocco, and Argentina have high uncertainty in the

disaggregation of reconstructed catch estimates by gear type from SAU due to

large amounts of unreported data and unidentied species in their catch reports.

Bottom trawling is growing rapidly in many Asian countries. In the

last two decades China has become the country with the highest

bottom trawl catch, accounting for 15 percent of global catch

from bottom trawling over the past decade. The country has also

seen explosive growth in its bottom trawling catch of nearly 400

percent in the last four decades, from 1.4 million tonnes in 1985 to

5.2 million tonnes in 2015. Vietnam has the second highest bottom

trawl catch and shares a border with China, putting extra pressure

on sh stocks in the region. Vietnam also has the largest bottom

trawl eet in Southeast Asia – approximately 20,000 vessels (both

bottom trawling and pelagic trawling) and about twice the size of

Indonesia’s eet.cxc Vietnam has seen over 7,000 percent growth

in bottom trawling since the 1970s, while India and Myanmar have

both seen more than 400 percent growth.

Bottom trawling levels might be even higher than SAU data

suggests in countries such as Indonesia, North Korea, and

the Philippines. Unpublished Global Fishing Watch (GFW)15

near-shore radar detections indicate that levels of bottom

trawling may be even higher than those estimated by SAU in

15 Global Fishing Watch (GFW) is an international non-prot that uses vessel GPS data,

including AIS and synthetic aperture radar (SAR), to track vessel locations globally. These data

sources can be used to identify undetected near-shore vessels that can serve as a proxy for

estimating bottom trawling effort in the EEZs of countries which supply their data to GFW.

many Asian countries, including Indonesia, North Korea, and

the Philippines where automatic identication system (AIS)

coverage is limited. Additionally, through SAU data and expert

interviews, the authors are aware of several regions where there

are “mini-trawlers” or “small trawlers” that might not get picked

up by radar, including Cambodia, Indonesia, the Philippines, the

US Gulf of Mexico, the North Sea, and the Mediterranean.

In many African and European countries more than half of the

total catch comes from bottom trawling, suggesting very high

reliance on the practice (see Table 7). Given the importance

of this shing method to the seafood sector in these regions,

any efforts to reduce bottom trawling would require signicant

investment, capacity building, and provisioning for a successful

transition to support eet diversication or a just transition.

Table 7 Top 10 countries ranked by the percentage of

their total EEZ catch from bottom trawling gears.

Country Average bottom trawl

catch (2007-2016) in

millions of tonnes

Percentage of sea-

food catch from

bottom trawling

The Netherlands 0.09 65

Morocco* 1.8 65

Somalia* 0.1 64

Vietnam* 2.3 59

Guinea* 0.5 59

Côte d’Ivoire 0.1 56

Germany 0.9 55

Republic of

the Congo 0.05 54

Guyana 0.03 53

New Zealand 0.4 53

Average bottom trawl catch represents average values for the most

recent decade for which data is available (2007-2016). Only countries

with at least 10,000 tonnes/year are included.cxci

*Morocco, Somalia, Vietnam, and Guinea have high uncertainty in the

disaggregation of reconstructed catch estimates by gear type due to large

amounts of unreported data and unidentied species in its catch reports.

Approximately half of all coastal countries have little or no

bottom trawling. Of 156 coastal countries, 73 have less than

10,000 tonnes per year caught in their EEZs through bottom

trawling. This includes several South and Central American

countries and territories such as Colombia, Venezuela, French

Guiana, Honduras, and Belize (which banned the practice in

2010). While bottom trawling may not be a major presence

in these waters, from a global perspective, even low levels of

catch or short durations of bottom trawling can have relatively

large impacts on marine habitats. Furthermore, global trends

and lessons from Asia show that growth in use of the gear

can occur rapidly and foreign bottom trawl eets often push

into underexploited EEZs if demersal sh stocks in their home

waters show decline.

6. Global extent

New perspectives on an old shing practice: Scale, context and impacts of bottom trawling32

Global extent of environmental impact

Mirroring catch, the ecological impact of bottom trawling

is not evenly distributed. Bottom trawling’s effects on

overshing, bycatch, and habitat can be more a function of

the intensity of effort rather than the overall catch amounts

throughout an EEZ. An individual bottom trawl shery can

occur along an entire coastline, or target one seabed area

for repeated exploitation, meaning that the ecological

impacts are dependent on the characteristics of the specic

bottom trawl sheries. Bottom trawling intensity, a measure

of how often a region is shed with bottom trawling gears,

determines the environmental impact on specic seabed

areas. Where specic vessel location data is unavailable,

bottom trawling intensity can be estimated by dividing the

total catch in an area by the size of that area.

Average bottom trawl intensity is highest in nearshore

territorial seas and the EEZs of a few West African and

Southeast Asian countries (see Figure 7). Intensity estimates

(as measured by catch per unit area) for territorial seas are on

average more than twice the rate of intensity estimates within

EEZs – approximately 0.4 tonnes/km2/year in territorial seas

versus 0.2 tonnes/km2/year in EEZs. Areas close to shore

tend to be shed by artisanal and small-scale shers, which

may contribute to conict between artisanal shers and

industrial bottom trawlers. At the EEZ level, bottom trawling

intensity is highest in Guinea, Guinea-Bissau, Morocco, South

Korea, Cambodia, Thailand, and Cameroon, which suggests

that the seabed of these nations is strongly impacted by

bottom trawling. Of this group, Guinea stands alone with more

than 5 tonnes of bottom trawl catch/km2/year, over 1.5 times

the intensity of neighboring Guinea-Bissau. However, low

average intensities as measured by catch/area may indicate

that an area that has been historically trawled is already

depleted, rather than reecting less activity from bottom

trawling vessels. For example, the Mediterranean appears to

have a lower catch/area from bottom trawling which may be

reective of the low levels of catch due to depleted stocks,

rather than lack of bottom trawl activity, as there are several

thousand bottom trawl vessels active in the region.cxcii

Another measure of trawling intensity is swept area ratio

(SAR), the sum of the area swept by bottom trawls divided

by the area of the region. The Mediterranean and Northern

Atlantic regions appear to have the highest trawling

intensity as measured by SAR. Amoroso et al. (2018) used

high-resolution satellite vessel monitoring system (VMS)

and logbook data on 24 continental shelves to nd that the

highest SAR bottom trawling intensity occurred in the Adriatic

Figure 7

Bottom trawling density estimates in EEZs between 2007 and 2016.

tonnes/km2/year

00–0.25 0.25–1.10 1.10–1.40 1.40–1.60 >1.60

Figure 7 Bottom trawling intensity estimates in EEZs between 2007 and 2016.cxciii

6. Global extent

New perspectives on an old shing practice: Scale, context and impacts of bottom trawling 33

Sea and the region west of Iberia.cxciv The study found that

trawling footprints are mostly localized and take up less than

10 percent of the area in almost half of the regions studied.

However, when scaled to the entire area of continental

shelves globally, bottom trawling is still the single largest

anthropogenic physical disturbance of global seabed habitats.

The estimated global bottom-trawled area of 1.1 million km2/

year is at least 10 times larger than the 100,000 km2/year of

forest lost to deforestation.cxcv,cxcvi

Furthermore, climate change may contribute to shifting sh

stock ranges, which could widen the existing footprint of

bottom trawling as shers seek to adjust their shing effort in

response. Fish have been observed to shift into new territory

at a rate of 70 km per decade as a result of climate change,

with shifts expected to accelerate going forward.cxcvii,cxciii

The reach of several countries’ bottom trawling eets

extends well beyond their own EEZs and into the waters of

other countries. Understanding the global extent of bottom

trawling and its environmental and social impacts requires

looking at not just where the shing is happening, but who

is doing it. Around the world, 22 percent of all bottom trawl

during the most recent decade of available data occurred on

foreign-agged ships in other countries’ EEZs (see Figure 8).

This gure could be even higher, given that a signicant

amount of distant-water shing is thought to be illegal,

unreported, and unregulated, and is thus dicult to track.

In 34 countries, predominantly in Africa, over 90 percent of

the catch caught by bottom trawlers in the EEZ is caught by

foreign-agged vessels. With few exceptions, the countries

with the highest overall catch from bottom trawling – such

as China, Vietnam, Indonesia, and India – also have the

highest overall catch from bottom trawling by their eets

shing in foreign waters.

Foreign-agged bottom trawling vessels are

predominantly of Asian and European origin and operate

primarily in Africa and Oceania. Over half of the bottom-

trawl catch landed in Africa and Oceania is caught by

vessels with Asian or European ags. In contrast, almost all

the bottom trawl catch in Asia, Europe, and the Americas is

caught by trawlers agged to the country in which they sh.

China deploys bottom trawlers in the EEZ of nearly every

country in West Africa and is the primary shing entity in

Côte d’Ivoire, Ghana, Guinea-Bissau, Liberia, and Togo.

The presence of foreign bottom trawling has implications

for local livelihoods, economies, and politics. Though the

social implications of foreign bottom trawling are not well

documented at the global level, various regions have long

histories of associated conict. In West Africa, foreign

bottom trawlers have played a critical role in shaping local

dynamics (See Section 5: State of the evidence: socio-

economic impacts).cciii Social unrest, violence and food

insecurity in Mauritania and The Gambia are connected to

the foreign shmeal factories that are primarily sustained

by foreign trawlers, with many trawlers actively shing

in areas reserved for artisanal shers.cciv,ccv,ccvi Although

trawlers mostly target pelagic species, pelagic or midwater

trawling in some cases takes place in shallow waters and

can effectively act as a bottom trawl. Bottom trawling is

illegal in Somalia, yet bottom trawlers are responsible for 6

percent of total foreign catch in the country.ccvii While this

may be a relatively small amount, bottom trawlers have

disproportionately inuenced the overall Somali perception

of foreign shing and have come to symbolize the conict

between foreign and domestic shers.ccviii In South Asia,

increasing animosity between Indian and Sri Lankan bottom

trawlers has resulted in violent and even deadly conict over

shing access.ccix

Foreign access agreements for bottom trawlers often

come at the expense of local shers and coastal

communities. Governments establish agreements with

foreign bottom trawlers under the pretense of increasing

economic benet domestically. However, many of these

agreements result in local shing communities losing

access to valuable resources. This in turn threatens coastal

livelihoods and economic growth in the long term. A recent

study found that the foreign shing access agreements for

bottom trawl sheries in West Africa generated revenues

between 2-8 percent of the estimated landed value of the

harvest.ccx In other words, West African governments are

agreeing to signicant trade of critical resources without

getting much in return.

Distant water shing and bottom trawling

6. Global extent

New perspectives on an old shing practice: Scale, context and impacts of bottom trawling34

The overall effect of bottom trawling on stock status and

recovery post-trawling in non-target benthic species is

not well documented, but there are indications of regional

concern. Hilborn et al. (2021) recently published a review of

349 individual stocks constituting 90 percent of the global

groundsh catch (which are traditionally caught via bottom

trawl) and found that, on average, stock abundance is

increasing and is currently above the level that would produce

maximum sustainable yield.cxcix However, the study showed that

in several parts of the world with high levels of bottom trawling

including Japan, Russia, Chile, and Argentina, groundsh stocks

continue to be below sustainable biomass levels. Mazor et

al. (2020) found that most species are depleted by only a few

percent where bottom trawling occurs, though this gure can

be up to 14 percent in Europe where trawl intensity is high

and has persisted for decades. However, these studies failed

to consider the impact on structure-forming species, harm

to which is viewed by many marine ecologists as a potential

ecological threat of bottom trawling. For example, ecological

damage to non-sh species such as sponge and corals from

bottom trawling has been identied in the Aleutian Islands, and

the disturbance could take over three decades to recover.cc

Additionally many bottom trawl sheries are in parts of

the world where stocks are unassessed or where sheries

governance is weak, such as West Africa, Southeast Asia,

India, and China.cci, ccii

Figure 8

Flow of annual bottom trawl catch (in tonnes) from foreign-flagged vessels.

17,692,600

Asia

16,233,000 tonnes

of annual bottom trawl catch

Africa

4,139,300

2,279,000

Europe

2,038,400

Africa

Europe

1,327,200

South

America

961,300

889,400

South

America

North America

273,200

Oceania

254,000

244,800

North America

43,800

Oceania

FISHING ENTITY (FLAG)

FISHING AREA

Figure 8 Flow of annual bottom trawl catch (in tonnes) from foreign-agged vessels

6. Global extent

About half of the total bottom trawl catch within African EEZs is from vessels with Asian or European ags.ccxi

New perspectives on an old shing practice: Scale, context and impacts of bottom trawling 35

The Positive Disruption

Paradigm

Paths forward

New perspectives on an old shing practice: Scale, context and impacts of bottom trawling36

Avoiding, minimizing, or mitigating

environmental impacts

There are generally two broad categories of approach when

it comes to addressing the environmental impacts of bottom

trawling: manage its worst impacts or fundamentally limit

the practice.

1. Measures to manage impacts. This set of interventions uses

the conventional tools of sheries management (monitoring,

enforcement, input and output controls) to manage shing

effort for bottom trawls in the same way that other shing

methods might be managed. Many of these approaches

are not unique to bottom trawls and operate under the

fundamental assumption that the environmental impacts of

all shing methods can be managed. These interventions

can be categorized into four types:

• Technical, gear, and vessel measures that change

operations in order to improve eciency, increase yield,

or achieve legal compliance (e.g., increased mesh sizes

to allow less retention of juveniles, electronic monitoring,

bycatch reduction devices). These could also include

measures that apply only to bottom trawling to reduce

bottom trawl-specic impacts (e.g., devices that reduce

bottom contact, penetration depth, or fuel consumption;

modications that affect weight and durability of gear;

“move-on” rules when sensitive species are identied in

trawl catch; use of pre-catch image identication software

to increase selectivity).

• Spatial and temporal controls (non-gear-specic and gear-

specic) to protect target species at vulnerable life stages

or VMEs (e.g., the protection of nursery grounds and

spawning areas, seasonal closures, marine protected areas

that ban industrial uses, no-take zones).

• Output controls to limit the amount of seafood that can

be caught in a given shery, which may or may not include

bycatch or habitat impact quotas.

• Effort controls that affect the number and types of vessels

that can exert bottom trawling effort.ccxii

Fisheries management interventions require relatively good

governance and coastal community buy-in to be successful

and effective. Given that most bottom trawl sheries

occur in parts of the world with relatively weak sheries

governance (see Section 6: Global extent) the tools of sheries

management have often been criticized as not appropriate or

ineffective in these contexts.ccxiii,ccxiv,ccxv These tools are unlikely

to make sense in parts of the world which lack the ability to

monitor or enforce these kinds of solutions.

2. Measures to limit the practice. This set of interventions

refers to efforts to severely limit the footprint of bottom

trawl eets under the assumption that bottom trawling has

unique environmental impacts that are socially, politically or

otherwise unacceptable, and for which the tools of sheries

management are unlikely to be effective. These often include

measures beyond the sheries management toolkit (e.g.,

bans, campaigns, articial reefs, subsidy reform, ecosystem-

based management). These interventions can include:

• More aggressive gear-specic spatial measures to restrict

bottom trawling (e.g., “no trawling” standards in MPAs, IEZs,

VME closures, MPA “minimum standard” laws to protect

essential habitats; “freezing the footprint” approaches)

• Complete prohibitions such as national-level gear-specic bans

• Deterrents such as anti-trawling devices (e.g., articial reefs

built of large concrete blocks)

• International laws, standards, and agreements that seek

to constrain the practice (e.g., subsidy reform at the World

Trade Organization, prohibitions within international waters,

regional ecosystem-based management approaches).

Minimal evidence exists to systematically evaluate and

compare the effectiveness of different approaches to manage

or limit bottom trawling. Conventional sheries management

approaches –particularly those addressing capacity (i.e., effort

and output controls) – have seen declines in bottom-trawled

target species reversed in some temperate trawl sheries.ccxvi

However, whether changes in trawl shing effort drive

improvements at an ecosystem level has not been conclusively

demonstrated and many advocates remain unconvinced

that stable catches of trawled species offer a suciently

robust indication of a healthy marine environment. While

more comprehensively addressing impacts unique to these

sheries, bottom trawl-specic measures – particularly the

more stringent approaches such as national bans or large

inshore exclusion zones – can be highly contentious and

lead to signicant additional social conict (e.g., the Costa

Rica and Indonesia bottom trawl bans), especially in cases

where the costs of retiring licences, scrapping trawl vessels

and redeploying trawl workforces have not been adequately

identied or covered by the state. ccxxvii,ccxxviii Such dramatic

measures may yield straightforward benets, such as

increases in non-trawl catches (particularly where trawlers and

non-trawlers are targeting similar species groups)ccxix, higher

biomass of high trophic level species, increases in extent of

sensitive seabed habitats, and increased diversity in seabed

ecological communities.ccxx, ccxxi,ccxxii

7. Paths forward

This section seeks to build on the common

understanding of the extent and impacts of bottom

trawling discussed in previous chapters by presenting

possible paths forward that acknowledge the broader

context and importance of the sector. It concludes

with recommendations for constructive action.

New perspectives on an old shing practice: Scale, context and impacts of bottom trawling 37

Through expert consultation the report authors identied

several real-world examples that demonstrate the success

of both measures to manage and limit bottom trawling’s

environmental impacts. There are examples of NGOs, the

shing industry, academia, shing communities, and civil

society successfully working together globally to try to

minimize the harmful impacts of the practice, and in cases

where those impacts are deemed unacceptable, to severely

constrain it (see Table 8). Efforts that align with existing

political will and collaboration with the seafood industry appear

to have been more effective in minimizing the bottom trawling

sector’s impact while not fundamentally changing the status

quo. However, many advocates argue that these efforts do not

go far enough in protecting vulnerable ecosystems and that

more aggressive measures are needed.

Table 8 Examples of measures to manage or limit

bottom trawling’s environmental impacts

Examples of measures

to manage

Examples of measures to limit

• China’s central

government passed

a mandate to reduce

shing capacity

that resulted in a 10

percent decrease

in bottom trawling

vessels.ccxxiv

• WWF-Russia has

worked with the

MSC-certied pollock

sheries in the

Barents Sea to model

and transition to

“gentle trawl” gears

that signicantly

reduce environmental

impacts.ccxxv

• In South Africa, the

hake bottom trawl

shery voluntarily

gave up 5 percent of

the EEZ to trawling in

response to pressure

from the MSC and

NGO objections

• The United Kingdom banned

bottom trawling in four MPAs

as part of an effort to show

improved support for marine

conservation.ccxxv

• In Costa Rica, the tourism

industry, sport shing sector,

small-scale sector, and longline

sector joined forces to advocate

against the domestic bottom

trawling sector, resulting in a

constitutional ban.ccxxvi

• In Madagascar, small-scale

shers successfully got permits

for foreign bottom trawlers

revoked by the government

after incursions into their

shing area.

• The Deep Sea Conservation

Coalition engaged in a

successful 17-year effort

to work with the UN to

acknowledge and formally

recommend limits to bottom

trawling in VMEs on the

high seas.

All of these interventions imply tradeoffs; therefore,

which solutions make sense will depend on what sheries

managers, communities, governments, and NGOs deem to

be priorities, and the resources available for implementation.

While minimal habitat impacts especially for sensitive species

or areas may be desirable from an environmental perspective,

or a reduced overall carbon footprint to stay within planetary

boundaries, competing objectives might include maintaining

employment in the bottom trawl sector, or supporting the

aquaculture feed sector and the food it provides to urban

consumers. Awareness and management of the inherent

tradeoffs in these complex systems is critical.

Avoiding, minimizing, or mitigating social

impacts

More work is needed to identify solutions that can avoid,

minimize, or mitigate negative social and economic outcomes

of bottom trawl eets – especially for structurally vulnerable

or marginalized groups.ccxxvii The pervasive social challenges

(and in some cases human rights abuses) associated with

seafood production have only recently received attention from

the marine conservation community and the seafood industry.

Although tools like the Monterey Framework for Social

Responsibility outline a set of goals for social responsibility

in the seafood industry, the framework is far from being

widely adopted by the seafood sector and faces signicant

resistance from both the conservation community and the

seafood industry.ccxxviii The Transform Bottom Trawling Coalition

explicitly calls for four actions to reduce both environmental

and social impacts: 1) strengthening national IEZs for small-

scale shers, 2) prohibiting bottom trawling in all MPAs, 3)

ending harmful subsidies to bottom trawlers while supporting a

fair and just transition for all those affected, and 4) prohibiting

the expansion of bottom trawling to new, untrawled areas.

Sharing best practices for managing the social and economic

impacts of bottom trawl sheries as well as examples of

successful transitions could help shing communities, the

seafood industry, and NGOs envision a future whereby at

a minimum, bottom trawl sheries do no further social or

economic harm.

Possible solutions to support positive and just social

outcomes could follow the outline presented by the High

Level Panel for a Sustainable Ocean Economy: safeguards,

mainstreaming equity, and transformative approaches.ccxxix

The association between bottom trawl sheries and human

rights abuses suggests that basic human rights are not being

protected in this subset of the shing sector and that stronger

safeguards are required. Human rights due diligence is one

such approach that is increasingly being piloted in the seafood

sector – which is arguably long overdue in comparison to other

food and commodity sectors. An additional safeguard should

be the protection of exclusive access for small-scale shers,

especially in the nearshore zone or territorial seas. This is

consistent with the FAO Guidelines for Small-Scale Fisheries

that, as of yet, are purely voluntary. IEZs are one promising

tool (see Section 5: State of the evidence: socio-economic

impacts) that would benet from greater enforcement and

institutional support. Other transformative approaches

7. Paths forward

New perspectives on an old shing practice: Scale, context and impacts of bottom trawling38

could include economic transition packages that go beyond

pure vessel buybacks, which are rife with challenges, and

towards approaches to help actually transition shers and

shworkers out of bottom trawling and into retraining in

equally compensated or similar sectors, or retirement. Similar

programs are being considered under the moniker of a “just

transition” away from fossil fuels, recognizing that these

transitions will hit fossil fuel workers rst and worst. Given

that global bottom trawling eets are highly uneconomical

even with subsidies, the time may be ripe to reconsider more

benecial redirection of those resources.ccxxx

Further consideration of the social and political dimensions

of a transition either towards more limited bottom trawling, or

away from the practice entirely, may create new opportunities

to achieve more positive outcomes for people and nature.

Efforts to limit bottom trawling have historically been

contentious, due to signicant political, cultural, nancial, and

even environmental obstacles. Yet in many parts of the world

governments, communities, civil society, and the seafood

industry itself are looking for solutions to the impacts of this

method of seafood production that is often highly subsidized,

economically inecient, with an aging workforce, and which

has environmental, climate, and social impacts that are

increasingly challenging to justify. It is important for any

transition away from bottom trawling to avoid demonizing

those who currently work in the sector – especially in cases

where those working in the sector may support economically

fair and socially just transitions.

Strategies and solutions need to address the dependence

that many across the world have on this shing practice and

include viable alternatives to prevent undue harm to already

vulnerable communities. More creativity and experimentation

is needed from both the conservation community and seafood

sector to identify viable ways forward that do not further

marginalize shers, workers, and those already marginalized

by this sector. Thus, in 2010 in Belize, the environmental NGO

Oceana, working with local allies and the government of Belize,

after a public information campaign emphasizing the need

for sustainable sheries, was able to achieve a legislated

ban on all trawling in the EEZ by arranging the purchase and

decommissioning of a pair of aging trawlers.ccxxxv

Just transitions in the

bottom trawl shery

Just transitions represent strategies to move away from

extractive economies.ccxxxi They are rooted in labor unions

and the environmental justice movement and are meant

to ensure that workers impacted by economic shifts can

equitably access pathways to new opportunities. Although

just transitions can look very different depending on the

context they are considered in, they ultimately share a

set of core principles including 1) guaranteed pathways

to quality jobs, 2) training and retraining support, and 3)

worker transition funds.

There have been no well documented just transitions in

the bottom trawling eet. However, Hong Kong’s 2012

trawl ban and associated buyout scheme serves as an

example of a type of economic package that can support

the transition away from bottom trawling.The buyout

scheme included 1) compensation to trawl vessel owners

who stopped shing in inshore waters, 2) introduction of

the voluntary buyout scheme with a one-year transitional

period, and 3) payment to crew members affected by

the trawl ban.ccxxxii Training and technical support were

offered to shers who wanted to transition to other shing

operations.ccxxxiii The buyout scheme amounted to $219

million, which included payment for affected shing

crew members.ccxxxiv Part of the buyout scheme included

plans to sink some of the shing vessels so they could

be used as articial reefs to improve the local marine

environment. Hong Kong’s buyout scheme gives insight

into what countries with similar resources and contexts

could potentially achieve. However, more work is needed to

ensure a true just transition.

7. Paths forward

New perspectives on an old shing practice: Scale, context and impacts of bottom trawling 39

Recommendations for constructive action

The authors recommend that sheries decision-makers,

managers, shing industry leaders and advocates prioritize

the following nine high-level actions to transform bottom

trawling for better environmental and socio-economic

outcomes (under the acronym “TRANSFORM”):

• Transition the system: Bottom trawling supports a set of

complex, distinct food and non-food commodity systems

that are globally interconnected. Solutions must take into

account broader dynamics – such as broad social changes

in shing culture, the rise of the global seafood trade, and

food consumption patterns – in order to avoid unintended

consequences, such as effort displacement. Solutions

to manage or limit bottom trawling should not be viewed

in isolation by policymakers, shery managers, NGOs, or

communities.

• Respect human rights: To catalyze meaningful

improvement in bottom trawl sheries requires a human-

centered approach. This means respecting both the civil and

political rights, as well as the economic, social and cultural

rights of those working in and affected by such sheries.

Bottom trawl sheries – and policy changes relating to

them – must abide by a minimum standard of “do no harm.”

More baseline research into socio-economic impacts and

possible solutions (especially distributional impacts) should

accompany these efforts.

• Accelerate the transition to best practices: Modern

management practices – from gear innovation to enhanced

observer coverage – have dramatically improved the

performance of some bottom trawl sheries, particularly in

stabilizing overexploited stocks, increasing selectivity, and

reducing seabed pressure especially in VMEs. Urgent effort

is needed to export these practices to regions that need

them most, particularly in low- and middle-income countries

in the tropics.

• Negotiate political action: Decision-makers must recognize

the unique biodiversity, climate and social conict

challenges associated with bottom trawling and legislate

for it as a special case – both through national policies and

international standards and agreements. As well as making

bold, gear-specic policy decisions, this should also include

acknowledging the signicant investments and trade-offs

needed to adequately resource any transition away from

bottom trawling.

• Stop harmful subsidies: Denitions of “harmful” subsidies

must include those accessed by specic sheries using the

highest impact practices, including bottom trawl sheries.

Conversely, subsidies supporting transition out of (or to

improve) practices such as bottom trawling should be

considered “benecial.”

• Freeze the footprint: Given the multitude of unresolved

challenges around bottom trawling – at global and local

levels – any new or expanded sheries should be regarded

as politically, socially, environmentally, and economically

inappropriate.

• Open up dialogue: Discourses around bottom trawling

from the sheries and conservation sectors do not tend to

emphasize common ground. Bold alliances and painful but

necessary compromise are needed to meet the twin climate

and biodiversity crises, including between sectors with

different material interests.

• Restrict appropriately: Ecologically and culturally sensitive

areas must be protected from bottom trawling through a

coherent area-based approach, encompassing inshore and

offshore exclusion zones as well as all classications of

marine protected areas.

• Monitor impact to support adaptive management: While

all best-practice sheries require signicant volumes of

real-time information, bottom trawling management (with its

reliance on expensive and complex seabed sensitivity data)

necessitates robust, collaboratively funded research. As

well as near-term management-focused monitoring, special

attention should be directed to emerging areas of trawling

research, especially life cycle analysis and carbon emissions

arising from seabed disturbance.

This report has made the case that bottom trawling is an

important and unique subset of the global shing industry.

Bottom trawling as a shing practice has its own specic

impacts and requires a combination of conventional and

transformative solutions to manage them. With this synthesis

of evidence, the report authors believe the time is right to

reconsider some of the stale perspectives that have plagued

discussion of this sector and contributed to its ongoing

environmental, social, and climatic challenges. There is a

possible future that is both just and sustainable, through the

best that science, advocacy, and industry action have to offer.

7. Paths forward

New perspectives on an old shing practice: Scale, context and impacts of bottom trawling40

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Fisher Conict, Ethnicity and Nation-State.”

cxxxvii A. Menon et al, “The Political Ecology of Palk Bay Fisheries: Geographies of Capital,

Fisher Conict, Ethnicity and Nation-State.”

cxxxviii

S.M. Glaser, P.M. Roberts, and K.J. Hurlburt, “Foreign Illegal, Unreported, and

Unregulated Fishing in Somali Waters Perpetuates Conict,” Frontiers in Marine Science

6 (2019), https://doi.org/10.3389/fmars.2019.00704; N.

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New perspectives on an old shing practice: Scale, context and impacts of bottom trawling 43

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CEA Consulting

Montgomery Street,

San Francisco,

CA 94104, USA

E: john@ceaconsulting.com

T: +1 415-421-4213

Fauna & Flora International

The David Attenborough Building,

Pembroke Street, Cambridge,

CB2 3QZ, UK

E: info@fauna-ora.org

T: +44 1223 571 000

The trawl supremacy: hegemony of destructive bottom trawl fisheries and some of the management solutions

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Sep 2021
REV FISH BIOL FISHER

Fisheries resources in Hong Kong have been overexploited since the 1970s due to intensive bottom trawling and other fishing activities that have depleted stocks and destroyed marine habitat. To rehabilitate depleted fisheries resources, a permanent ban on trawling in Hong Kong territorial waters came into force on December 31, 2012. In order to determine whether the trawl facilitated recovery of fish communities, trawl surveys were conducted at two sites in each of the eastern, southern and western (estuarine) coastal waters of Hong Kong before and three years after the trawl ban. A total of 315 species and 86 families of fishes in nine feeding groups were encountered during the surveys. Mean trophic level of the fish community, abundance and biomass of total fishes and of predatory fishes increased in eastern and western waters after the ban, but no changes or declines in these metrics were observed in southern waters. Although initial recovery in fish community were observed in eastern and western waters, anthropogenic disturbances might hinder the recovery process, including a large-scale reclamation for construction of coastal infrastructures in the west, illegal trawling, and expansion of non-trawling fishing efforts in the southern and eastern waters. Longer term monitoring is needed to evaluate the effects of the trawl ban, and determine whether recovery in the southern waters will continue to be constrained by the anthropogenic disturbances. Graphic abstract

Blue food demand across geographic and temporal scales

Article

Full-text available

Sep 2021

Numerous studies have focused on the need to expand production of ‘blue foods’, defined as aquatic foods captured or cultivated in marine and freshwater systems, to meet rising population- and income-driven demand. Here we analyze the roles of economic, demographic, and geographic factors and preferences in shaping blue food demand, using secondary data from FAO and The World Bank, parameters from published models, and case studies at national to sub-national scales. Our results show a weak cross-sectional relationship between per capita income and consumption globally when using an aggregate fish metric. Disaggregation by fish species group reveals distinct geographic patterns; for example, high consumption of freshwater fish in China and pelagic fish in Ghana and Peru where these fish are widely available, affordable, and traditionally eaten. We project a near doubling of global fish demand by mid-century assuming continued growth in aquaculture production and constant real prices for fish. Our study concludes that nutritional and environmental consequences of rising demand will depend on substitution among fish groups and other animal source foods in national diets. Global demand for “blue food” is growing. In this quantitative synthesis, the authors analyse global seafood demand and project trends to 2050, finding considerable regional variation in the relationship between wealth and consumption.

Global status of groundfish stocks

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Full-text available

May 2021

We review the status of groundfish stocks using published scientific assessments for 349 individual stocks constituting 90% of global groundfish catch. Overall, average stock abundance is increasing and is currently above the level that would produce maximum sustainable yield (MSY). Fishing pressure for cod‐like fishes (Gadiformes) and flatfishes (Pleuronectiformes) was, for several decades, on average well above levels associated with MSY, but is now at or below the level expected to produce MSY. In contrast, fishing pressure for rockfishes (Scorpaeniformes) decreased from near MSY‐related levels in the mid‐1990s, and since the mid‐2000s has remained on average at only one third of MSY‐related levels. Regions with the most depressed groundfish stocks are the Northwest Atlantic and the Pacific coast of South America, while stocks from the Northeast and Eastern Central Pacific, Northeast Atlantic, Southeast Atlantic and Southwest Pacific tend to have greatest average abundance relative to MSY‐based reference points. In the most recent year available for each stock, the catch was only 61% of MSY. Equilibrium yield curves indicate that 76% of global potential groundfish yield could be achieved using current estimates of fishing pressure. 15% of this is lost by excess fishing pressure, 67% results from lower than optimal fishing pressure on healthy stocks and 18% is lost from stocks currently overfished but rebuilding. Thus, there is modest opportunity to increase catch of global groundfish fisheries by reducing overfishing on some stocks, but more by increasing harvest on others. However, there may be other reasons not to fully exploit these stocks.

Organic carbon densities and accumulation rates in surface sediments of the North Sea and Skagerrak

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Full-text available

Mar 2021
BG

Continental shelf sediments are places of both rapid organic carbon turnover and accumulation, while at the same time increasingly subjected to human-induced disturbances. Recent research suggests that shelf sediments might have a role to play as a natural climate solution, e.g. by storing organic carbon if left undisturbed from anthropogenic activity. However, we have an incomplete understanding about the centres of organic carbon accumulation and storage on continental shelves. To better constrain the rate of accumulation and the mass of organic carbon that is stored in sediments, we developed and applied a spatial modelling framework that allows us to estimate those quantities from sparse observations and predictor variables known or suspected to influence the spatial patterns of these parameters. This paper presents spatial distribution patterns of organic carbon densities and accumulation rates in the North Sea and Skagerrak. We found that organic carbon stocks and accumulation rates are highest in the Norwegian Trough, while large parts of the North Sea are characterised by low stocks and zero net accumulation. The total stock of organic carbon that is stored in the upper 0.1 m of sediments amounted to 230.5 ± 134.5 Tg C, of which approximately 26 % is stored in the Norwegian Trough. Rates of organic carbon accumulation in the Norwegian Trough are comparable with those reported from nearby fjords. We provide baseline datasets that could be used in marine management, e.g. for the establishment of “carbon protection zones”. Additionally, we highlight the complex nature of continental shelves with zones of rapid carbon cycling and accumulation juxtaposed, which will require further detailed and spatially explicit analyses to constrain sedimentary organic carbon stocks and accumulation rates globally.

A 20-Year Retrospective Review of Global Aquaculture

Article

Full-text available

Mar 2021

The sustainability of aquaculture has been debated intensely since 2000, when a review on the net contribution of aquaculture to world fish supplies was published in Nature. This paper reviews the developments in global aquaculture from 1997 to 2017, incorporating all industry sub-sectors and highlighting the integration of aquaculture in the global food system. Inland aquaculture—especially in Asia—has contributed the most to global production volumes and food security. Major gains have also occurred in aquaculture feed efficiency and fish nutrition, lowering the fish-in–fish-out ratio for all fed species, although the dependence on marine ingredients persists and reliance on terrestrial ingredients has increased. The culture of both molluscs and seaweed is increasingly recognized for its ecosystem services; however, the quantification, valuation, and market development of these services remain rare. The potential for molluscs and seaweed to support global nutritional security is underexploited. Management of pathogens, parasites, and pests remains a sustainability challenge industry-wide, and the effects of climate change on aquaculture remain uncertain and difficult to validate. Pressure on the aquaculture industry to embrace comprehensive sustainability measures during this 20-year period have improved the governance, technology, siting, and management in many cases.

Protecting the global ocean for biodiversity, food and climate

Article

Full-text available

Mar 2021
NATURE

The ocean contains unique biodiversity, provides valuable food resources and is a major sink for anthropogenic carbon. Marine protected areas (MPAs) are an effective tool for restoring ocean biodiversity and ecosystem services1,2, but at present only 2.7% of the ocean is highly protected³. This low level of ocean protection is due largely to conflicts with fisheries and other extractive uses. To address this issue, here we developed a conservation planning framework to prioritize highly protected MPAs in places that would result in multiple benefits today and in the future. We find that a substantial increase in ocean protection could have triple benefits, by protecting biodiversity, boosting the yield of fisheries and securing marine carbon stocks that are at risk from human activities. Our results show that most coastal nations contain priority areas that can contribute substantially to achieving these three objectives of biodiversity protection, food provision and carbon storage. A globally coordinated effort could be nearly twice as efficient as uncoordinated, national-level conservation planning. Our flexible prioritization framework could help to inform both national marine spatial plans⁴ and global targets for marine conservation, food security and climate action.

Long-Term Change of Demersal Fish Assemblages on the Inshore Agulhas Bank Between 1904 and 2015

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Full-text available

May 2020

Without baseline data from near pristine assemblages, measures of ecosystem change may be significantly underestimated. A unique historical dataset provided an opportunity to investigate long-term change in demersal fish assemblages of South Africa’s inshore trawl grounds. Three sites surveyed over a period from 1903 to 1904 were re-surveyed in 2015 using replicated historical gear and methods. Catch composition was contrasted between historical and modern periods using unconstrained ordination, permutational multivariate analysis of variance, permutational tests of the homogeneity of multivariate group dispersions and similarity percentage analyses. After 111 years, the re-survey revealed a drastically transformed demersal assemblage, with the period effect explaining nearly half of the variance among samples. Historical catches were dominated by kob (Argyrosomus spp.), panga (Pterogymnus laniarius) and east coast sole (Austroglossus pectoralis), jointly contributing 70–84% of the catch. The same taxa made up a minor component (1.5–5.5%) of modern assemblages. Instead, the re-survey catches consisted predominantly of gurnards (Chelidonichthys spp.), Cape horse mackerel (Trachurus capensis), spiny dogfish (Squalus spp.), shallow-water hake (Merluccius capensis), and white sea catfish (Galeichthys feliceps), with their summed contribution rising to 85% from the historical 3%. These results suggest that a century of trawling may have altered benthic habitats, indirectly contributing to changes in the fish community. Historical assemblages included a substantial proportion of taxa that associate with reef habitats, whereas the re-survey assemblages were characterized by species that inhabit unconsolidated sediments or both reef and non-reef habitats. The unique historical context and data, comparable gear and methods and long temporal period revealed striking baseline changes that may be overlooked in most fisheries. Reconstructing this important historical context improves our ability to assess, interpret and manage changing marine ecosystems.

China’s policies on bottom trawl fisheries over seven decades (1949–2018)

Article

Nov 2020
MAR POLICY

To pursue sustainable fisheries, the world needs to constrain bottom trawling (BT) through effective management. Such change is particularly urgent for China, which operates one of the largest bottom-trawl fisheries (BTF) both in and beyond its waters. We provide the first comprehensive review of China’s approach to BTF over seven decades (1949 – 2018) based on bibliometric approaches (diversity index, network and word-cloud analyses). We collated an inventory of 103 Chinese national policies and classified them into seven categories (e.g., input/output control) over five eras: (i) E1: 1949 – 1977 (planned fishing with limited management); (ii) E2: 1978 – 1992 (regime shift with input control); (iii) E3: 1993 – 2002 (EEZ management with multiple regulations); (iv) E4: 2003 – 2012 (resource conservation with balanced measures); and (v) E5: 2013 – 2018 (fisheries transformation towards sustainability with bans ahead). We found that China has increased its concerns on BTF, with more frequent and diverse policies over time. Such changes included more limits (e.g., input and output controls) and more law enforcement. However, little was known about the effectiveness of many policies, and some well-intentioned ones (including bans) failed in implementation. We indicate that these policies have been influenced by both domestic (e.g., political will, consumption demand) and international drivers (e.g., international laws, globalization). We highlight the problems in managing China’s BTF, and challenges and suggestions in policy implementation. This review may help policy making and implementation for BTF management in China and facilitate the dialogue between China and the world in fishery policies for sustainable development.

A Path to a Sustainable Trawl Fishery in Southeast Asia

Article

Jun 2020

Trawl fishing constitutes an important part of the marine fisheries sector in Southeast Asia. It provides livelihoods and food for millions of people in coastal communities as well as feed for the region’s growing aquaculture sector. Trawl fisheries suffer from a multitude of problems, including overcapacity, excessive fishing effort, poor profitability and inadequate governance. The historical decline in catch per unit of effort, increasing proportion of low-value fish in trawl catches, widespread illegal fishing, and user conflicts reflect the weak management of these fisheries. Various measures implemented in the region have been insufficient to achieve sustainable outcomes. There has been little incentive for fishers to satisfactorily comply with the regulations. To understand better what kind of approaches would be effective and workable, the specific characteristics of SE Asian trawl fisheries are described and the fundamental barriers that must be addressed to improve sustainability and social benefits are identified. Meeting these challenges needs consideration of the socio-economic insecurity and the lack of alternative livelihoods as well as the complex ecological, cultural and institutional characteristics in the region. Simple, robust, equitable and easily enforced management measures are likely to work best in such a challenging environment. Properly implemented co-management systems would help to create incentives for individuals to cooperate. Trust building, participatory approaches, strong leadership and capacity building are important components to move SE Asian fisheries toward sustainability targets.

Understanding gear choices and identifying leverage points for sustainable tropical small-scale marine fisheries

Article

Feb 2020
OCEAN COAST MANAGE

In rural coastal areas of most countries of the Global South, small-scale fisheries (SSF) are the main source of food and income, and a key driver of local economies. Ensuring sustainability of SSF requires an understanding of socio-economic and cultural contexts and consideration of the drivers of fishers' behaviour, in particular in terms of spatial and temporal fishing patterns and gear choice. In this study, we assess the contribution of SSF to local fish consumption, explore drivers behind fishers' gear choice and compare the profitability of different fishing gears used in the Colombian Pacific coast, providing context to a discussion on SSF management strategies. We estimated a mean annual fish consumption of 237 kg per capita in the study area, which is higher than most estimates from coastal communities worldwide. Bottom trawls, a gear type banned by the fishing authority, had appealing characteristics for fishers with limited income opportunities: low investment and maintenance costs, low operational risks, high value of target species and high profitability. Users of gillnets of small mesh size (≤2.75”) targeted the most valuable species in the market, white shrimp (Penaeus occidentalis), but their catch-per-unit-effort (CPUE) and associated profit varied between villages, likely related to spatial patterns of resource abundance and fishing effort. Longlines were used by a small percentage of fishers who had a higher perception of theft risks than other gear user groups. Commonly used leverage points for SSF sustainability, such as an economic compensation to fishers or redistribution of fishing effort from illegal to legal gears, could also be combined with more impactful ones, such as facilitating fishers’ organizational capacities and empowerment for co-management schemes. Our results provide an essential - and often overlooked - socio-economic perspective for managers in tropical SSF that aim to pursue a holistic approach to fisheries management, based on an improved understanding of the incentives and constraints that influence fishing behaviour.

New perspectives on an old fishing practice: Scale, context and impacts of bottom trawling

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