Cover:
Illustration by Emanuela D’Antoni.
GUIDELINES TO REDUCE
SEA TURTLE MORTALITY
IN


FISHING OPERATIONS
FOOD AND AGRICULTURE ORGANIZATION OF THE UNITED NATIONS
Rome, 2010
Reprinted 2010
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ISBN 978-92-5-106226-5
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© FAO 2009
Preparation of this document
Reports and materials prepared at two international meetings were central to
the development of these technical guidelines. The meetings were the Expert
Consultation on Interactions between Sea Turtles and Fisheries within an
Ecosystem Context (Rome, 9–12 March 2004) and the Technical Consultation
on Sea Turtles Conservation and Fisheries (Bangkok, 29 November to
2 December 2004). The important contribution of the participants to both
meetings is acknowledged.
The document was prepared by Eric Gilman, FAO visiting scientist and IUCN
Marine Programme, and Gabriella Bianchi, Food and Agriculture Organization of
the United Nations (FAO), Fisheries Management and Conservation Service
(FIMF), and edited by Claire Attwood. The cover page and several of the figures
contained in these guidelines were prepared by Emanuela D'Antoni (FAO, FIMF).
The Government of Japan is thanked for providing funding for the above meetings
and for the preparation and printing of these guidelines, through the trust fund
project GCP/INT/919/JPN; the Government of the United States of America for
providing part of the funding for the Technical Consultation.
Contributions and comments to earlier drafts of this document were provided by
Hiroshi Minami, National Research Institute of Far Seas Fisheries, Japan; John
Watson, John Mitchell, Jeff Gearhart, Charles Bergman and Lesley Stokes,
NOAA Fisheries Service, United States of America; Lindsay Chapman and Steve
Beverly, Secretariat of the Pacific Community; and Karen Eckert, Wider
Caribbean Sea Turtle Conservation Network and Duke University.
Frank Chopin (FAO, Fishing Technology Service, FIIT) and Wilfried Thiele (FAO,
consultant) thoroughly revised later drafts of the document and their important
contribution is acknowledged.
iii
FAO Fisheries and Aquaculture Department.
Guidelines to reduce sea turtle mortality in fishing operations.
Rome, FAO. 2009. 128pp.
Sea turtles are affected by a range of different factors, some natural and others
caused by human activities, including fishing operations. As a result, all sea turtle
species whose conservation status has been assessed are considered to be
threatened or endangered. These guidelines provide assistance for the
preparation of national or multilateral fisheries management measures and
industry initiatives that may help to conserve sea turtles by reducing the negative
impacts that fisheries may have on them. The guidelines are voluntary and non-
binding. Their scope is global, but when they are implemented, national and
regional diversity, including cultural and socio-economic differences, should be
taken into account. These guidelines present our best understanding of how to
reduce interactions between sea turtles and fishing gear and reduce the
proportion of caught turtles that are killed as a result of interactions with marine
capture fisheries. They include information about how to change fishing gear and
fishing methods and how the fishing industry can adopt voluntary approaches to
reduce sea turtle mortality. The guidelines make suggestions about implementing
management actions, such as input and output controls and bycatch fees, and
they cover subjects such as bycatch hotspot avoidance, best practices for the
handling and release of caught turtles and reducing derelict fishing gear and other
marine debris. They also identify fisheries and areas where fishing may be a
relatively important cause of sea turtle deaths. Research, monitoring, information
exchange, capacity-building, financial support, socio-economic, cultural and legal
aspects are also discussed.
ABSTRACT
iv
CONTENTS
Preparation of this document . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iii
Abstract. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iv
Abbreviations and acronyms. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . vii
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Guidelines for marine capture fisheries to reduce sea
turtle interactions and mortality . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
Background. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Identification, distribution and biology of sea turtles . . . . . . . . . . . . . . . . . . . . 3
Threats to sea turtles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Sea turtle interactions in marine capture fisheries . . . . . . . . . . . . . . . . . . . . 12
High risk areas, high risk fisheries and information gaps . . . . . . . . . . . . . . . 13
The role of IGOs, including RFMOs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Fishing gear designs and fishing methods . . . . . . . . . . . . . . . . . . . . . . . . . . 20
Gillnet fisheries . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
Pelagic longline fisheries . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
Circle hooks and fish bait . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
Deeper setting. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
Dyed bait . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
Soak time . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
Other gear technology strategies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
Trawl fisheries . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
Hard TEDs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
Soft TEDs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
Purse seine fisheries . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
Demersal longline fisheries . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59
Pound nets/traps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61
Best practices for sea turtle handling and release . . . . . . . . . . . . . . . . . . . . 62
Sea turtle bycatch hotspot avoidance. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70
Time-area closures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70
Fleet communication . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74
Input controls–fishing effort and capacity limits . . . . . . . . . . . . . . . . . . . . . . 75
Output controls–sea turtle caps, target species caps . . . . . . . . . . . . . . . . . . 76
Bycatch fees and other methods of compensation. . . . . . . . . . . . . . . . . . . . 76
Avoidance and reduction of derelict fishing gear and other marine debris . . 77
v
Retrieval of derelict fishing gear and other debris . . . . . . . . . . . . . . . . . . . . 77
Consideration of effects on other sensitive species groups . . . . . . . . . . . . . 80
Observer, logbook and landings data collection . . . . . . . . . . . . . . . . . . . . . . 81
Research and commercial demonstrations . . . . . . . . . . . . . . . . . . . . . . . . . 84
Information exchange . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85
Provide or exchange equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87
Industry self-policing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88
Economic incentives: ecolabelling and sustainable seafood programmes. . 88
Global instruments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91
Regional level . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92
National level . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96
Production and distribution of educational and training materials . . . . . . . . 99
Training workshops. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100
Technology, skills transfer and technical support . . . . . . . . . . . . . . . . . . . . 100
Research, monitoring and information exchange . . . . . . . . . . . . . 81
Incentives for industry participation . . . . . . . . . . . . . . . . . . . . . . . . . 87
Legal and policy frameworks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91
Technical and institutional capacity building, outreach
and education. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99
Financial support for the implementation of guidelines
in developing countries . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101
Socio-economic and cultural considerations . . . . . . . . . . . . . . . . 103
Reporting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105
Further additional reading . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107
Glossary of terms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111
Annex I. Guidelines to Reduce Sea Turtle Mortality
in Fishing Operations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115
Annex II. Regional fishery bodies and other intergovernmental
organizations responsible for regional sea turtle
conservation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 122
Annex III. Research results on the effects of circle vs. tuna and
J hooks and alternative types and sizes of bait on catch
rates of target and bycatch species in pelagic longline
fisheries (courtesy of John Watson, NOAA, United
States of America). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 125
vi
Abbreviations and acronyms
BRD
bycatch reduction device
CBD
Convention on Biological Diversity
CCRF
FAO Code of Conduct for Responsible Fisheries
CCSBT
Commission for the Conservation of Southern Bluefin Tuna
CITES
Convention on International Trade in Endangered Species of Wild
Fauna and Flora
CMS
Convention on Migratory Species
COFI
FAO Committee on Fisheries
EEZ
exclusive economic zone
FAD
fish aggregating device
FAO
Food and Agriculture Organization of the United Nations
GFCM
General Fisheries Commission for the Mediterranean
IAC
Inter-American Convention for the Protection and Conservation of
Sea Turtles
IATTC
Inter-American Tropical Tuna Commission
ICCAT
International Commission for the Conservation of Atlantic Tunas
IGO
intergovernmental organization
IOTC
Indian Ocean Tuna Commission
IPOA
international plan of action
IUU
illegal, unreported and unregulated fishing
MoU
memorandum of understanding
MPA
marine protected area
MSC
Marine Stewardship Council
NAFO
Northwest Atlantic Fisheries Organization
NGO
non-governmental organization
OFCT
Overseas Fishery Cooperation Foundation
OLDEPESCA Latin American Organization for Fisheries Development
OPRT
Organization for the Promotion of Responsible Tuna Fisheries
RFB
regional fishery body
RFMO
regional fisheries management organization
SEAFO
South East Atlantic Fisheries Organization
SSH
sea surface height
SST
sea surface temperature
TAC
total allowable catch
TED
turtle excluder device
UNCLOS
United Nations Convention on the Law of the Sea
UNFSA
United Nations Fish Stocks Agreement
VMS
vessel monitoring system
WCPFC
Western and Central Pacific Fisheries Commission
vii
Introduction
Background
The FAO Code of Conduct for Responsible Fisheries (CCRF) calls for the
sustainable use of aquatic ecosystems and requires that fishing be conducted
with due regard for the environment. Article 7.2.2d of the CCRF specifically
addresses biodiversity issues and conservation of endangered species and, in so
doing, calls for the catch of non-target species, both fish and non-fish species, to
be minimized. The CCRF also promotes the maintenance, safeguarding and
conservation of biodiversity by minimizing fisheries impacts on non-target species
and the ecosystem in general.
These guidelines were developed to support the implementation of the CCRF.
They are addressed primarily to decision-makers within fisheries management
authorities and to interest groups such as fishers, fishing companies, fishers'
organizations, relevant non-governmental organizations (NGOs) and others.
They aim to help these interest groups to identify and implement appropriate
measures to reduce interactions with sea turtles and thereby help to address the
issue of sea turtle mortality in fishing operations.
Kemp’s ridley turtle
(Lepidochelys kempi)
Hawksbill sea turtle
(Eretmochelys imbricata)
Olive ridley turtle
(Lepidochelys olivacea)
Figure 1. The seven species of sea turtles
1
Leatherback turtle
(Dermochelys coriacea)
Flatback turtle
(Natator depressus)
Green sea turtle
(Chelonia mydas)
Loggerhead turtle
(Caretta caretta)
Figure 1. Continued.
2
Sea turtle identification key
These guidelines were drafted at the request of the FAO Committee on Fisheries
(COFI), which raised the question of sea turtle conservation at its 25th session.
They are the product of two international meetings: an Expert Consultation on
Interactions between Sea Turtles and Fisheries within an Ecosystem Context
(March 2004) and a Technical Consultation on Sea Turtle Conservation and
Fisheries (November/December 2004). "Guidelines to Reduce Sea Turtle
Mortality in Fishing Operations" were developed at the latter meeting.
These guidelines were endorsed at the 26th session of the COFI, which called for
their immediate implementation by members and regional fishery bodies (RFBs).
They also provided the key inputs for the preparation of these guidelines.
The key objectives of these guidelines are to: (i) present measures for avoiding or
minimizing sea turtle interactions in marine capture fisheries; and (ii) consolidate
existing handling and release guidelines.
There are seven species of sea turtles, i.e. the loggerhead (Caretta caretta), the
green turtle (Chelonia mydas), the hawksbill (Eretmochelys imbricata), the
Kemp's ridley (Lepdochelys kempi), the olive ridley (L. olivacea), the flatback
(Natator depressus) and the leatherback turtle (Dermochelys coriacea) (Figure 1).
In the areas where they co-occur, they can easily be distinguished (see
identification key below).
Identification, distribution and biology of sea turtles
Dermochelys coriacea
Leatherback turtle
FAMILY DERMOCHELYIDAE
1a.
Carapace (dorsal part of shell) with 5 distinct ridges running the
length of the animal; flippers without claws.
3
Carapace with no ridges, consisting of large hard scutes; flippers with one or more claws.
FAMILY CHELONIDAE
1b.
2a. Carapace with 4 lateral scutes
3a. Beak smooth, hawklike; 2 pairs of scales between eyes;
flippers with 2 claws; carapace elliptical; underside with 4
lateral scutes, without pores
3b. Beak serrated; 1 pair of scales between eyes; 4 scales
posterior to eyes; flippers with 1 evident claw; carapace oval;
underside with 4 lateral scutes
3c. Beak smooth; 1 pair of scales between eyes; 3 scales
posterior to eyes; flippers with one evident claw; carapace
round and flattened, with slightly upward-folded margins;
underside with 4 lateral scutes without pores
Natator depressus
Flatback turtle
Eretmochelys imbricata
Hawksbill sea turtle
Chelonia mydas
Green sea turtle
4
2b. Carapace with 5 lateral scutes
4a. Carapace elongated, its length always greater than its width;
underside with 3 lateral scutes without pores.
4b. Carapace nearly round, its length similar to its width;
underside with 4 lateral scutes.
5a. Carapace with usually 6 or more lateral scutes;
pantropical, usually between 20° C surface
isotherm.
5b. Carapace with 5 lateral scutes; restricted distribution,
adults mainly in the Gulf of Mexico and off the east
coast of the United States of America, to about 16º N.
Caretta caretta
Loggerhead turtle
Lepidochelys olivacea
Olive ridley turtle
Lepidochelys kempii
Kemp's ridley turtle
5
Most sea turtles are widely distributed in tropical and subtropical waters of all
oceans. A few species have a more restricted distribution, such as the Kemp's
ridley with adults occurring in the Gulf of Mexico and juveniles with a broader
distribution reaching northern European waters, and the flatback, confined to
northern Australian waters (Figure 2a–2g).
Areas of possible occurrence
Main distribution areas
Figure 2a. Leatherback turtles (Dermochelys coriacea) are circumglobal, found from tropical to
temperate regions.
Figure 2b. Hawkbill sea turtles (Eretmochelys imbricata) are the most tropical of all sea turtles,
found throughout central America and the Indo-Pacific Region.
Figure 2c. Green sea turtles (Chelonia mydas) are widely distributed in tropical and subtropical
waters, near continental coasts and around islands.
6
Figure 2d. Flatback sea turtles (Natator depressus) are indigenous to northwestern, northern, and
northeastern regions of Australia and have the most restricted range of all sea turtle species.
Figure 2e. Loggerhead sea turtles (Caretta caretta) are circumglobal, from tropical to temperate
habitats.
Figure 2f. Olive ridley sea turtles (Lepidochelys olivacea) are found in the tropical regions of the
Atlantic, Indian and Pacific Oceans.
Figure 2g. Adult Kemp's ridley sea turtles (Lepidochelys kempii) usually occur in the Gulf of Mexico.
Juveniles and immatures range between temperate and tropical coastal areas of the northwestern
Atlantic Ocean. Occasionally, young turtles reach northern European waters and as far south as the
Moroccan coast.
7
Coastal shallow water benthic feeding zone(s)
Figure 3. Life cycle and main habitats
1
1 After Lanyon, J.M., Limpus, C.J. & Marsh, H. 1989. Dugongs and turtles: grazers in the seagrass system.
In:
Biology of Seagrasses: A Treatise on the Biology of
Seagrasses with Special Reference to the Australian Region, pp. 610–634. Amsterdam, Elsevier.
A.W.D. Larkum, A.J. McComb & S.A. Shepherd (eds),
Immature turtles
Adults
Age at first breeding
about 20–50 years
Breeding
migration
Adult males and females
Return to
feeding areas
Breeding migration
at 2–8 year intervals
Mating
Occurs offshore to
nesting beaches
Nesting beach
Several clutches of eggs are laid
Open ocean surface
feeding zone
“The lost year(s)”
Adult females
2 weekly
intervals
All species of sea turtles are long-lived, slow-growing species, characterized by a
complex life cycle and utilizing a wide range of habitats (Figure 3). Sexual maturity
is delayed in all species, with estimates varying in different species and
populations, but usually exceeding 20, even 50, years. After mating, females dig
nests in sandy beaches, and lay from 50 to 130 eggs per nest. Hatchlings crawl to
seawater and swim towards the open ocean. After a period of time that varies
according to species, juveniles return to coastal waters to feed on benthic
organisms.
8
Exceptions to this general pattern are the leatherback turtles, which remain
pelagic throughout their life cycle, and the flatback turtles, which remain neritic
throughout their lives. As the turtles grow and reach sexual maturity, both males
and females leave their feeding grounds and migrate to the nesting beach. This
periodic migration will continue throughout their lives. Females dig nests in dry
sand, returning faithfully to the same beach each time they are ready to nest and
returning to the sea either to rest before nesting again later that season or before
beginning their migration back to their feeding ground.
These factors have an impact both in the terrestrial part of their habitat as well as
in the marine environment. Impacts in the nesting environment (on sandy
beaches) include: the direct take of adults for meat, oil, shells, etc.; the collection
of eggs by humans; the predation of eggs by animals (e.g. dogs, pigs); climate
change, which may affect embryo development; sea-level rise, a consequence of
global warming that in some circumstances results in a reduction of nesting beach
habitat; loss of nests due to hurricanes; and heavy utilization of nesting beaches
by humans.
Threats to sea turtles
Because of their long life span, a life cycle that requires several habitat types, and
their extensive distribution in terms of the distance they cover, sea turtles are
affected by a range of different factors, some natural and others caused by human
activities, at all stages of their life cycle (Figures 4a–d and 5).
Figure 4. Examples of major threats to sea turtles
Figure 4a. Fibropapilloma tumours and pollution
9
10
In the marine environment, threats derive from
fishery interactions; pollution
(sea turtles eat a wide variety of marine debris such as plastic bags, plastic and tar
balls, balloons); and boat collisions, particularly in coastal waters.
Reliable data on sea turtle abundance and on the numerous causes of turtle
deaths, which are necessary for accurate population assessments, are generally
not available. In addition to a lack of data, it has proved difficult to identify all the
factors that influence the abundance of sea turtles.
climate change effects, including:
changes in sea temperature, currents and oceanographic processes such as El
Niño phases of the El Niño Southern Oscillation;
In addition, a disease known as fibropapilloma, a tumorous growth that kills sea
turtles, is now affecting large numbers of sea turtles around the world. It has been
hypothesized that this epidemic, which is believed to be linked to toxic ocean
pollution, is affecting sea turtles’ immune system.
One of the greatest threats to sea turtle populations is capture in fishing gear.
Longlines, trawls, gillnets and other types of gear catch sea turtles unintentionally,
as bycatch.
As mentioned, because of the
highly migratory nature of sea turtles and the large amount of hatchlings coupled
with low survival rates, it is difficult to estimate overall populations.
Figure 4b. Tourism and coastal development
There is, however, evidence that some sea turtle populations have declined
dramatically in recent decades, and all sea turtle species whose conservation
status has been assessed, are considered to be threatened or endangered. For
example, it is estimated that the number of nesting leatherback turtles in the
Pacific Ocean has declined by more than 95 percent in the past 20 years, and the
number of nesting loggerheads has declined by about 80 percent over the same
period. Unless action is taken soon, these sea turtles could disappear from the
Pacific Ocean in the near future.
Actions that reduce interactions between fisheries and sea turtles, as well as
initiatives that address other threats to sea turtles, may contribute to the recovery
of turtle populations.
11
Figure 4d. Boat collisions
Figure 4c. Plastic bags/debris
Sea turtle interactions in marine capture fisheries
The expansion of fishing activities in coastal areas and on the high seas has
contributed to the decline of several sea turtle populations.
As sea turtles cross the oceans from nesting beaches to foraging grounds and
back again, they run the gauntlet of industrial and artisanal fisheries.
Turtles can become entangled in gillnets, pound nets, purse seines and the lines
associated with longline and trap/pot fishing gear. Turtles entangled in these
types of fishing gear may drown and often suffer serious injuries to their flippers
from constriction by the lines or ropes. In addition to entangling turtles, longline
gear can also hook turtles in the jaw, oesophagus or flippers. Trawls that are not
fitted with turtle excluder devices (TEDs) do not allow turtles to escape, which
may result in mortality through drowning. Fishing dredges, extremely heavy metal
frames dragged along the ocean floor, can crush and entrap turtles, causing
death and serious injury. In the Pacific, coastal gillnet and other fisheries
conducted from a multitude of smaller vessels are of increasing concern. These
artisanal fisheries can collectively have a very great impact on local turtle
populations, especially leatherbacks and loggerheads, and this issue is only now
gaining international attention.
Sea turtle interactions are known to be problematic in pelagic longline, gillnet, set
net, pound net, trawl, purse seine and demersal longline fisheries that operate in
the range of sea turtles, especially in the tropics and subtropics. For example,
entanglement of leatherback turtles in surface set gillnets may be so frequent
during the leatherback nesting season in some areas of the Caribbean that it
causes expensive damage to gear, leading to time-consuming repairs. As a result,
Figure 5. Example of interactions between sea turtles and longline fishery
12
it is economically difficult for some gillnet fishers to operate when leatherbacks are
most abundant, a period that accounts for a substantial part of the year.
Progress in reducing turtle interactions has more recently been achieved in shrimp
trawl fisheries and pelagic longline fisheries, in both coastal and high seas fisheries
for tunas, swordfish and other pelagic fish. Little progress has been made in
reducing turtle interactions in purse seine fisheries, but assessments indicate turtle
bycatch rates in purse seine fisheries, including entanglement in fish aggregating
devices (FADs) deployed in these fisheries, is low relative to pelagic longline and
gillnet fisheries. Turtle interactions in coastal artisanal fixed net fisheries, such as in
gillnet, set-net, pound net and other fishing gear, is only now gaining international
attention and mitigation measures are not yet well developed.
The FAO Expert Consultation (FAO, 2004a) identified geographical areas where
there is a high likelihood that interactions between sea turtles and fisheries could
have a negative impact on sea turtle populations. For example, coastal fisheries
may affect females migrating for nesting purposes, as well as juveniles and
subadults. Trawls, gillnets, pelagic longlines and set-nets can potentially catch
sea turtles when they are used in areas of sea turtle occurrence. Sea turtle
populations that may be seriously affected by fishing operations and therefore
require urgent attention include the:
Pacific loggerhead;
Pacific leatherback;
Eastern Indian coast olive ridley.
To significantly reduce the impact of coastal fisheries on these most threatened
sea turtle populations, it is recommended that attention be focused on fisheries
management solutions in the following fisheries and regions:
coastal trawl fisheries off southeast Asia;
coastal gillnet fisheries off southeast Asia;
coastal gillnet fisheries in south Asian waters;
coastal trawl fisheries in south Asian waters;
coastal gillnet fisheries in southeast Pacific waters;
coastal gillnet fisheries in Baja California;
coastal demersal longline fisheries in the southeast Pacific and Baja
California waters; and
pelagic longline fisheries in eastern Pacific waters.
High risk areas, high risk fisheries and information gaps











13
Furthermore, there are regions and fisheries where information is largely
unavailable and the FAO Expert Consultation (2004a) recommended that basic
information be urgently collected for:
coastal trawl and gillnet fisheries in the western Indian Ocean;
coastal fisheries in the eastern Mediterranean; and
coastal and offshore fisheries of the eastern central Atlantic.
Interactions between sea turtles and high seas pelagic longline fisheries targeting
tunas and swordfish and operating primarily in the tropics and subtropics are a
concern. The high seas pelagic longline fisheries that set baited hooks in the
upper 100 m of the water column are believed to have an order of magnitude
higher sea turtle interaction rate than deeper setting longline fisheries. Use of
mitigation measures is therefore most urgent for those longline fisheries that
operate in relatively shallow waters (less than 100 m), in areas where sea turtles
occur and during times and seasons when they are particularly abundant.
According to the FAO Expert Consultation (2004a), longline fisheries are believed
to pose a major threat to the following sea turtle populations:
North and South Pacific loggerhead turtles;
Eastern Pacific leatherback turtles; and
Mediterranean Sea loggerhead and green turtles; mainly in the central and
western parts of the Mediterranean Basin, loggerheads are also threatened
by pelagic drifting gillnets (drift nets).
The report of the Expert Consultation also drew attention to the migration pattern
of turtles:
North Pacific loggerheads that originate in Japan migrate throughout the
North Pacific, mainly between 28 and 40°N;
leatherbacks originating in the Western Pacific migrate to the North Pacific to
forage;
leatherbacks originating in the Eastern Pacific move to the South Pacific to
forage.









14
The role of IGOs, including RFMOs
In 2007, FAO conducted a review of initiatives by intergovernmental organizations
(IGOs), including regional fisheries management organizations (RFMOs) and
other RFBs, to address sea turtle interactions in marine capture fisheries. The
FAO found that there are no IGOs that have put in place legally binding measures
that require fishing vessels to implement sea turtle avoidance methods.
There are five RFMOs with responsibility for fisheries that interact with sea turtles.
Some of these organizations have begun examining sea turtle bycatch, or have
adopted voluntary measures to address bycatch as part of their overall fisheries
management schemes. In addition, there are three multilateral agreements with
the primary responsibility of regional sea turtle conservation. These instruments
address a range of sea turtle conservation and protection issues and incorporate
provisions to address interactions with fisheries. Although these agreements do
not have fisheries management authority, they do carry obligations for signatory
states to take bycatch-related actions for areas under their jurisdiction.
The chapter “Legal and Policy Frameworks” (p. 91) describes the global
instruments that provide a legal framework for governments to advance the
sustainable management of marine living resources, and it also describes the
RFMOs with management responsibilities for fisheries that interact with sea
turtles. Furthermore, Annex II lists: (i) RFMOs that directly establish measures to
manage sea turtle interactions in marine capture fisheries; (ii) RFBs that provide
members with scientific and management advice; (iii) scientific bodies that
provide scientific information and advice; and (iv) other IGOs with a responsibility
for regional sea turtle conservation.
Illegal, unreported and unregulated (IUU) fishing may pose a threat to sea turtles
because IUU vessels are unlikely to employ measures to reduce sea turtle
interactions and mortality. While it is beyond the scope of this report to review IGO
measures to address IUU fishing, several RFBs have taken steps to effectively
reduce IUU fishing, including instituting requirements for vessel monitoring
systems (VMS), managing lists of authorized (approved) and illegal vessels, port
and at-sea inspection programmes and trade documentation programmes.
15
Guidelines for marine capture fisheries to reduce
sea turtle interactions and mortality
One way to mitigate fisheries interactions with sea turtles is to avoid them;
however, this may be problematic as the same productive areas conducive to
fishing are attractive feeding grounds for sea turtles.
However, there is a wide range of management and technical methods developed
by researchers, industry, and fisheries administrations that may be used to reduce
sea turtle interactions and mortality in marine capture fisheries. The methods are
categorized according to the type of fishery to which they are suited, and the
advantages and disadvantages of each method are summarized for ease of
reference.
Examples of methods that can help to reduce sea turtle interactions and mortality
in marine capture fisheries include:
modifications to fishing gear (including bait) and fishing methods;
post-capture practices that can improve the survival prospects of sea turtles
after release;
area restrictions or seasonal restrictions on fishing operations;
voluntary communication between the fishing fleet to avoid sea turtle
hotspots;
input controls, such as controlling the type or amount of fishing;
output controls, such as limiting the catch through, for example, total
allowable catch (TAC) or quotas;
imposition of a bycatch fee or other compensatory methods;
avoiding the loss and discarding of fishing gear and other debris; and
retrieving derelict fishing gear and other debris at sea.









It must be noted that all technical measures, modification of fishing gear and/or
other management measures must be adapted to the conditions of areas, vessels
and gear used. There is no “one size fits all solution” in mitigation measures!
17
Table 1. Summary of methods used to reduce sea turtle interactions and increase the likelihood of
turtles surviving interactions with marine capture fisheries
18
Measure to reduce sea turtle interactions or injury
Empirical
evidence of
turtle avoidance
efficacy
Empirical
evidence of
economic
viability
Evidence of
practicality
Multiple fisheries
Handling and release practices
Time–area closures/marine protected areas (MPAs)
Fleet communication for real-time bycatch hotspot
avoidance
Limited entry
Limit on effort
Sea turtle interaction cap per fishery or per vessel
Bycatch fees or other compensatory mitigation
measures
Target species catch limit
Reduction of derelict fishing gear and other marine
debris
Changing gear type to one with a lower turtle
bycatch to target catch ratio
Gillnet fisheries
Lower-profile (narrower), stiffer nets
Deeper setting for surface gillnet fisheries
Use longer tie-downs or avoid their use in demersal
gillnets
Avoid exceeding a maximum threshold for mesh size
Pelagic longline fisheries
Replacement of J and tuna hooks with wider circle
hooks
Use of fish instead of squid for bait
Setting gear deeper
Use of dyed bait/camouflaged gear
Reduced gear soak time, e.g. increasing number of
sets per day
Avoidance of fishing in certain sea surface
temperatures
Use of intermittent flashing light sticks in place of
traditional continuous flashing light sticks and not
using luminous gear
Coastal trawl fisheries
Turtle excluder devices for shrimp fisheries
Purse seine fisheries
Avoidance of encircling sea turtles
Modified designs for fish aggregating devices (FAD)
Demersal longline fisheries
None
Y
N
Y
Y
Y
N
Y
N
Y
Y
Y
Y
N
Y
Y
N
N
Y
Y
Y
Y
N
N
Y
Y
Y
Y
N
Y
Y
Y
Y
N
Y
N
Y
Y
Y
N
N
Y
N
Y
N
N
Y
Y
Y
Y
Y
Y
N
Y
Y
Y
Y
Y
Y
N
Y
Y
Y
Y
Y
Y
Y
Y
N
N
Y
Y
Y
Table 1 summarizes the various methods used to reduce sea turtle interactions in
marine capture fisheries. It is important to note that the efficacy and commercial
viability of some strategies will be fishery-specific; an indication of success in
Table 1 does not mean that a measure will necessarily be effective across all
fisheries. Further investment may also be necessary to bring these methods to a
state where they are commercially viable.
It is necessary and beneficial to have direct industry involvement in the
development of fishery-specific sea turtle bycatch solutions because:
(i) Fishers are likely to have valuable knowledge and information relating to sea
turtle bycatch. Their knowledge can be helpful in finding effective and
practical solutions. This has been demonstrated through a number of
cooperative research initiatives, such as in the United States Atlantic
longline swordfish fishery, the Hawaiian longline fishery, as well as various
industry-led fleet communication protocols aimed at reducing bycatch.
(ii) While lessons learned in other fisheries will provide a useful starting point,
solutions to sea turtle bycatch problems may be fishery-specific. Some of
the factors that need to be taken into account when adapting bycatch
solutions are the size and species of turtle, the target species, vessel size
and design, fisher safety aspects, etc.
(iii) It is necessary to consider a method's effectiveness at reducing turtle
capture and injury, as well as its commercial viability. Methods that are
shown to be effective in reducing turtle bycatch in experiments may not be
employed as prescribed, or employed at all, if they are not convenient and
economically viable, or better yet, provide operational and economic
benefits to fishers.
By ensuring the direct participation of fishers in the development and testing of
bycatch avoidance methods, one is more likely to encourage a feeling of
ownership within the fishing industry and thereby achieve support, broad uptake
and effective use of the method.
19
20
Fishing gear designs and fishing methods
Gillnet fisheries
A gillnet is a curtain of netting that hangs in the water at various depths,
suspended by a system of floats and weights, or anchors. The netting is almost
invisible to fish as they swim into the gillnet. Fish may become entangled,
enmeshed or gilled in these nets. The size of gillnet meshes (common are
meshsizes between 5–40 cm, depending on target species) determines the size
of the caught fish. Small meshes will catch small fish like sardines, but for larger
species there is always a danger of becoming entangled in such nets. Gillnets with
larger meshes, designed to target large pelagic species or cod or salmon, will
allow small fishes to go through the meshes. Gillnets are considered
size-selective gear in relation to target species, but they are non-selective for
marine mammals, seabirds and turtles.
One special type of gillnet, the pelagic drift nets on the high seas, target species
such as swordfish and other billfish, sharks, mackerels and mahi mahi.
Sometimes drift nets are lost and turn into “ghost nets” that can trap marine life for
a certain time. However in most cases, lost pelagic gillnets collapse soon after
deployment and form bundles of nettings in which relatively few fish or other
marine organisms are caught. Therefore, the threat of lost pelagic gillnets to
marine turtles is low.
Coastal bottom gillnets are often set close to shore or laid atop reef flats, a primary
sea turtle feeding area. Turtles entangled in these nets face a high risk of
drowning.
In some demersal gillnet fisheries, tie-down ropes are typically used to maximize
the catch of demersal fish species. Tie-downs are lines that are shorter than the
fishing height of the net and connect the float and lead lines at regular intervals
along the entire length of the net. This modification creates a bag of slack webbing
that aids in “entangling” rather than “gilling” demersal fish species. Unfortunately,
this technique also poses an entanglement hazard to sea turtles that encounter
the gear. Several studies in North Carolina’s flounder gillnet fishery found that
lower profile nets without tie-downs significantly reduced the incidence of sea
turtle entanglement compared with traditional gillnets that contained twice as
Tie-down nets
- 25 mesh deep
- 15 cm stretch
- 90 cm tie-downs
Low profile nets
- 12 mesh deep
- 15 cm stretch
- No tie-down
Bag effect
No bag
effect
Escape
potential
up & out
Lead line
Float line with corks
Float line with corks
90–120 cm
tie-downs
Entanglement
potential amplified
Tie-downs increase entanglement
No tie-downs decrease entanglement
Turtle into net
Entanglement
potential reduced,
bounce out & turnaround
much webbing and contained tie-down ropes regularly placed throughout the
gear. Research has also demonstrated that entangled turtles have a higher rate of
escape when longer tie downs are used (Figure 6a–b).
21
Figure 6a. Gillnet equipped with tie-downs (turtles can become entangled)
Figure 6b. Gillnet with longer tie-downs (turtles can escape more easily)
In demersal gillnet fisheries, there is empirical evidence that the use of narrower
(lower profile) nets is an effective and economically viable method for reducing
interactions with sea turtles. This is due to the combined effect of the net being
stiffer, thereby reducing the entanglement rate of turtles that encounter the gear,
and the net being shorter, thereby reducing the proportion of the water column that
is fished and so reducing the likelihood of turtles encountering the fishing gear.
Furthermore, increasing tie-down length, or avoiding the use of tie-downs, has
also been shown to decrease turtle entanglement rates.
The low profile technique has also proved effective at reducing turtle interactions
in surface gillnet fisheries. Again, using lower profile nets reduces sea turtle
entanglement as a result of the net being stiffer and reducing the proportion of the
water column containing gear. Recent research in the Trinidad surface drift gillnet
fishery for mackerel demonstrated a 35 percent reduction in leatherback bycatch
rates through the use of lower profile nets. Catch rates of target species were not
significantly compromised.
The following have been suggested as potential strategies for avoiding sea turtle
entanglement in gillnet fisheries. However, all of these strategies require
additional testing:
Deeper setting may reduce turtle captures by avoiding the upper water
column where turtles are most abundant. However, experience has shown
that deeper setting may result in unacceptable reductions in the catch rates of
target species.
Using alternative net materials to reduce the risk of turtle entanglement.
Setting nets perpendicular to the shore to reduce interactions with nesting
females.
Using deterrents, including sonic “pingers”, shark silhouettes, lights or
chemical repellents.
Management approaches such as area or seasonal closures should also be
considered as a means of reducing turtle interactions in gillnet fisheries. For
these measures to be efficient, good information on seasonal patterns in the
distribution of sea turtles is required.
Alfaro-Shigueto, J., Dutton, P., Van Bressem, M. & Mangel, J. 2007. Interactions
between leatherback turtles and Peruvian artisanal fisheries. Chelonian Cons. and
Biol., 6(1): 129–134.





Further reading on sea turtle gillnet and pound net fisheries interactions
22
Chan, E.H., Liew, H.C. & Mazlan, A.G. 1988. The incidental capture of sea turtles in
fishing gear in Terengganu, Malaysia. Biol. Cons., 43: 17.
Cheng, I.J. & Chen, T.H. 1997. The incidental capture of five species of sea turtles by
coastal setnet fisheries in the eastern waters of Taiwan. Biol. Cons., 82: 235–239.
(Note: the gear type in this paper is a pound net, not a setnet.)
Eckert, S.A. & Eckert, K.L. 2005. Strategic plan for eliminating the incidental capture and
mortality of leatherback turtles in the coastal gillnet fisheries of Trinidad and Tobago.
WIDECAST Technical Report No. 5. Ministry of Agriculture, Land and Marine
Resources, Government of the Republic of Trinidad and Tobago, in collaboration with
the Wider Caribbean Sea Turtle Conservation Network (WIDECAST). Beaufort, USA.
30 pp.
Gearhart, J. & Price, B. 2003. Evaluation of modified flounder gillnets in southeastern
Pamlico Sound, N.C. Completion report for NOAA award no. NA 16FG1220 segment
1. Morehead City, USA, North Carolina Department of Environment and Natural
Resources, Division of Marine Fisheries.
Gearhart, J., Scott, A. & Eckert, G. 2007. Field tests to evaluate the target catch and
bycatch reduction effectiveness of surface and mid-water drift gillnets in Trinidad.
WIDECAST Information Document 2007-01. Beaufort, USA. 21 pp.
Julian, F. & Beeson, M. 1998. Estimates of marine mammal, turtle and seabird mortality
for two California gillnet fisheries: 1990–1995. Fish. Bull., 96: 271–284.
Lee Lum, L. 2006. Assessment of incidental sea turtle catch in the artisanal gillnet fishery
in Trinidad and Tobago, West Indies. Appl. Herpetol., 3: 357–368.
Peckham, S.H., Diaz, D.M., Walli, A., Ruiz, G., Crowder, L.B. & Nichols, W.J. 2007.
Small-scale fisheries bycatch jeopardizes endangered Pacific loggerhead turtles.
PLoS ONE, 2(10): e1041.
Price, B. & Brown, K. 2005. Evaluation of low profile flounder gillnets in southeastern
Pamlico Sound, North Carolina. Completion Report for ITP 1446. Morehead City, USA,
North Carolina Department of Environment and Natural Resources, Division of Marine
Fisheries. 24 pp.
Price, B. & Van Salisbury, C. 2007. Low-profile gillnet testing in the deep water region of
Pamlico Sound, NC. Completion report for Fishery Resource Grant 06-FEG-02, ESA
Scientific Research Permit 1563. Morehead City, USA, North Carolina Department of
Environment and Natural Resources, Division of Marine Fisheries. 19 pp.
23
Pelagic longline fisheries
Pelagic longlining is a commercial fishing technique that ranges in scale from
domestic artisanal fisheries to modern, industrialized fishing, which is often
conducted by distant water fishing nations (Figure 7).
Main target species are large tunas (Thunnus spp), swordfish (Xiphus gladius),
other billfishes (species of the family Istiophoridae), and dolphinfish (mahimahi,
Coryphaena spp). Longlines can be set to hang at varying depths depending on
the targeted species.
24
Figure 7. Pelagic longlining occurs throughout the world's oceans. This method of fishing has been
used since the nineteenth century and ranges from small-scale domestic artisanal fisheries using
small and sometimes open vessels (the top-left photograph shows small boats from Peru's artisanal
pelagic longline fleet), to modern mechanized industrial fleets from distant water fishing nations. The
top-right photograph shows medium-sized longliners at Pago Pago, a port in American Samoa,
while the bottom photograph shows a Japanese distant water pelagic longliner.
Figure 8. Generalized configuration of drifting longline.
(Lengths and material of floats, main and branch lines; number of hooks between floats; number and
placement of weights on branch lines type of hooks and bait and methods of setting and hauling vary
between fisheries and vessels in a fishery.)
Sea surface
Float
Float line
Main line
Baited hook
Branch line
Branch line
Baited hook
Main line
Float line
Float
Sea surface
Figure 8a. Long float line results in deeper settings
Figure 8b. Short float line results in shallower settings
25
Pelagic longline fleets use a range of different fishing practices and gear configurations.
Longlines commonly consist of a long main line from which individual hooks are
suspended at intervals of 80–120 m. They can be up to 100 km long and carry up to
3 500 barbed hooks. The hooks are attached to the main line by monofilament branch-
lines or gangions. Floats spaced along the main line keep it elevated horizonally in the
water, and the branch lines hang vertically from it (Figure 8a–b). A variety of bait is used,
with whole smaller fish, such as Atlantic mackerel and squid.
In 2002, purse seine fisheries caught about 58 percent of the total combined
weight of the principal market species of tunas. Longline fisheries caught
15 percent, pole-and-line fisheries 14 percent, “other” fisheries (coastal artisanal
gillnet, handline, etc.) 13 percent, and troll fisheries less than one percent
(Figure 9). Large longline vessels (> 24 m in overall length), including those with
freezer technology, target bluefin and bigeye tunas for the sashimi market. Total
catch by large longliners has been stable or slightly decreasing since the late
1990s, while catches by smaller coastal longliners (< 24 m in overall length) have
been increasing since the 1990s.
Catches from the Atlantic, Indian and Pacific Oceans produce about 10, 23 and
66 percent, respectively, of the total catch of the principal market species of tunas
(Figure 10). Increased catches of tropical tunas, primarily yellowfin and skipjack,
but also bigeye, by purse seine vessels, account for the majority of the observed
increased trend in total tuna landings.
All sea turtle species are affected by pelagic longlines, but the loggerheads and
leatherbacks are the most frequently caught species.
Several attempts have been made to quantify the number of sea turtles accidentally
caught in fishing operations every year. These studies usually apply to specific
areas and fisheries and are, therefore, poorly suited to extrapolate global estimates.
For example, in 2004, one study estimated that more than 200 000 loggerheads and
50 000 leatherbacks were taken as bycatch in pelagic longline fisheries in 2000.
Figure 9. Trends in weight of world reported landings of principal market species of tunas by fishing
gear type (redrawn and updated from Bayliff, Moreno and Majkowsky, 2005)
26
0
500 000
1 000 000
1 500 000
2 000 000
2 500 000
1950 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000
Longline
Pole and line
Purse seine
Others
Tonnes
Figure 10. Trends in reported landings of principal market species of tunas by ocean (redrawn and
updated from Bayliff, Moreno and Majkowski, 2005)
0
1 000 000
4 000 000
3 000 000
2 000 000
5 000 000
1950 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005
Pacific Ocean
Indian Ocean
Atlantic Ocean
However, it is likely that these numbers were overestimated because several
incorrect assumptions were made when extrapolating Hawaiian observer data to
foreign fishing fleets operating in the Pacific.
Turtle catch rates from swordfish and tuna vessels vary widely between fisheries
and even between vessels operating in the same fishery. For example, catch
rates range from zero to 14 loggerheads and from zero to 2.4 leatherbacks per
1 000 hooks. The Pacific-wide catch rate for leatherbacks is estimated to be
0.0275 turtles per 1 000 hooks (this figure is based on 20 000 leatherbacks caught
on 728 million hooks). However, estimated catch rates are affected by the fact that
individual turtles may be captured multiple times. This phenomenon results in the
overestimation of sea turtle mortality. For example, a study of the Italian fishery for
swordfish in the Mediterranean Sea revealed that 92 percent of caught
loggerheads had one or more hooks either lodged externally or internally (internal
lodging was revealed by x-ray analysis). Some turtles had as many as three hooks
lodged in their stomachs.
Swordfish are typically caught in shallower waters than tunas and therefore a
priority is to employ sea turtle avoidance methods that are effective and
commercially viable for use in fisheries targeting swordfish. Furthermore, the
distant water fishing fleets of Taiwan Province of China, Japan and Spain landed
the largest catches of swordfish in 1997. Together, these fishing nations account
for more than half of global swordfish landings.
27
Tonnes
While large, industrialized pelagic longline fleets from distant water fishing
nations are believed to have relatively high sea turtle mortality rates, some
coastal artisanal and small domestic longline fleets that set shallow gear may
also cause relatively high sea turtle mortality and thereby affect populations of
critically threatened turtles. This is as a result of the location of their fishing
grounds and their fishing methods and gear. For example, in Ecuador, the
artisanal longline fisheries for dolphinfish, swordfish and bigeye tuna use
relatively small J hooks and tuna hooks and set their fishing gear at shallow
depths. The fishing grounds overlap with high densities of east Pacific
leatherback turtles and olive ridley turtles. These turtles migrate through waters
around the Galapagos Islands after nesting in Mexico and Costa Rica. Another
example is provided by the longline dolphinfish surface fishery in Costa Rica
where olive ridley turtle capture rates are very high. Similarly, high numbers of
interactions between leatherback and loggerhead turtles and the Peruvian
coastal, artisanal, longline dolphinfish and shark fisheries have been
documented. Owing to the distribution of the world's most threatened sea turtle
populations, the pelagic longline fisheries of the eastern Pacific and
Mediterranean also represent a serious threat to turtles.
There are several fishing methods and gear modifications that have been
shown to reduce sea turtle interactions in longline fisheries significantly
without compromising catch rates of target species. These methods include:
(i) using wide circle hooks;
(ii) using fish rather than squid for bait; and
(iii) setting hooks deeper than turtle abundant depths (40–100 m).
Other strategies are currently being tested. These include:
(i) using relatively small circle hooks (= 4.6 cm narrowest width) in place
of narrower J and tuna hooks;
(ii) single hooking fish bait rather than threading the hook through the bait
multiple times;
(iii) reducing gear soak time and retrieving gear during daytime; and
(iv) avoiding bycatch hotspots through fleet communication programmes
and area and seasonal closures.
28
Circle hooks and fish bait
Circle hooks, J hooks and tuna hooks are three types of hooks in use in pelagic
longline fisheries. A circle hook is rounded with the point oriented perpendicular to
the shank, while a J hook is shaped as its name implies, with its point oriented
parallel to the hook shaft. In shape, a tuna hook is in between a circle and a J hook,
but the point of the tuna hook is not guarded by the shaft, as is the case for J hooks
(Figure 11). The point on a circle hook is turned in, towards the hook shank.
Experiments suggest that circle hooks are effective at reducing captures of hard-
shelled turtles because they are wider at their narrowest point than J hooks and
tuna hooks. Therefore, they are too wide to fit into the mouths of sea turtles. The
circle hook may also be effective at reducing leatherback captures because of its
shape; hard-shelled turtles tend to become caught in longline gear because they
bite a baited hook, while leatherbacks tend to become caught because they are
foul-hooked on the body or entangled in the line.
Different fisheries show different results
The effectiveness and commercial viability of a turtle avoidance strategy may
be fishery-specific. Its success may depend on the size and species of turtles,
the target species and other variables. It is therefore advisable to test sea turtle
avoidance methods in individual fleets and regions.
Figure 11. Main types of hooks used by longliners
29
J hook
Japanese tuna hook
Circle hook
There is a growing number of experiments that provide information about the
effects of hook and bait combinations on both sea turtle capture rates and target
species catch rates in pelagic longline fisheries. For example, in the United States
North Atlantic longline fishery for swordfish, the use of 18/0 circle hooks and squid
bait reduced loggerhead and leatherback bycatch rates by 86 percent and
57 percent, respectively compared with fishing with J hooks and the same bait.
When combined with mackerel bait (rather than squid bait), the 18/0 circle hook
reduced loggerhead and leatherback bycatch rates by 90 percent and 65 percent,
respectively, without compromising catch rates of swordfish. Similar results have
been observed in the Hawaiian longline swordfish fishery: capture rates of
leatherback and loggerhead turtles declined substantially – by 83 percent and
90 percent respectively – after switching from a J hook with squid bait to a wider
circle hook with fish bait.
In addition to reducing sea turtle capture rates, the use of circle hooks has been
shown to reduce the number of turtles that are deeply hooked, i.e. the hook is
swallowed into the oesophagus or deeper, rather than being hooked in the mouth or
foul hooked on the body. Mouth-hooked turtles probably have a greater chance of
surviving a hooking than deeply hooked turtles (Figure 12a–c).
Moreover, gear removal is more commonly accomplished with lightly hooked
turtles. For example, in the United States North Atlantic longline fishery for
swordfish, the use of circle hooks rather than J hooks substantially reduced the
proportion of deeply hooked sea turtles landed by the fishery. Similar effects were
observed in the Hawaiian longline swordfish fishery; after switching from J hooks
Figure 12a–c. Examples of hooking and entanglement
Figure 12a.
Mouth-hooked turtle
Figure 12b.
Deeply hooked turtle
(hook swallowed in the stomach)
Figure 12c.
Entangled turtle
30
and squid bait to wider circle hooks and fish bait, there was a significant reduction
in the number of turtles that swallowed hooks (into the oesophagus and deeper)
and a significant increase in the numbers of turtles that were released after the
removal of all terminal tackle, both of which are outcomes that may increase the
likelihood of turtles surviving the interaction.
In some fisheries, the use of circle hooks and fish bait has been shown to improve
catch rates of certain target species. For example, after a requirement was
instituted for vessels in the Hawaiian longline fishery for swordfish to use 18/0 circle
hooks with fish bait – in place of 9/0 J hooks with squid bait – the swordfish catch
rate increased significantly by 16 percent. However, catch rates of combined tuna
species and catch rates of combined mahimahi, opah, and wahoo declined
significantly, by 50 percent and 34 percent, respectively. Similar results were
Different shapes show different results
Circle hooks come in a variety of shapes and sizes. Different shapes can
change the performance of individual hooks. For example, a circle hook with a
o
larger gap between the point and the shank, or greater than a 10 offset, may
affect the hook's interactions with sea turtles.
Other differences in hook designs, such as the material from which the hook is
manufactured, may also affect sea turtle capture rates and position of hooking.
Unfortunately, there is no uniform system of hook measurements. This is
problematic when reporting research results and comparing results between
experiments and may be compounded by the fact that the different
manufacturers of hooks use different terminology.
observed in the United States Atlantic longline swordfish fishery. The reduction in
catch per unit effort (CPUE) for tuna species is likely due to the size of the fish bait
being used in these fisheries. Other studies have shown increases in CPUE for
tuna species when circle hooks were used in combination with smaller sized fish.
Reduced CPUE for the other fish species is likely due to the size of the circle hook
used.
Furthermore, several studies have demonstrated that switching from squid to fish
bait results in large (approximately 35 percent) and significant reductions in shark
catch rates. The effect on shark catch rates when switching to a circle hook from
J and tuna hooks is unclear, with conflicting results from different studies.
31
Figure 13a.
b.
c.
Generic outline (frontal and lateral view) of a circle hook to show main parts and how
the offset angle is measured;
example of non-offset hook (point of the hook in line with the
shank);
example of offset hook (point of the hook not in line with the shank)
b)
c)
Offset hooks
The influence of bait
Offset circle hooks are similar in shape to non-offset circle hooks, but the point is
not in line with the shank (Figure 13a–c). When laid on a flat surface, a non-offset
hook would lie flat, but the point of an offset hook would be slightly elevated.
Research has shown that using offset circle hooks with 10 degrees or less offset,
rather than non-offset circle hooks in longline fisheries, does not affect sea turtle
capture rates. Furthermore, the use of less than 10 degree offset circle hooks does
not seem to affect the location of turtle hooking. Circle hooks with more than a
10 degree offset behave similarly to J hooks and increase turtle capture rate and
increase the proportion of caught turtles that are deeply hooked when compared
with non-offset circle hooks. It may be possible that offset hooks result in increased
injury to turtles relative to non-offset hooks when a hook is ingested because the
offset hooks may be more likely to embed internally instead of passing through.
The use of circle hooks results in less foul hooking than J hooks. Leatherbacks are
most often foul hooked; it is likely that any size circle hook with minimal offset will
result in a reduction in leatherback bycatch.
Turtles have been observed to feed differently when feeding on squid and fish.
Observations of foraging captive turtles reveal that they tend to eat fish
progressively, in small bites, until they completely remove the fish from the hook
(Figure 14a). However, turtles tend to line up squid with their flippers and gulp it
down whole, ingesting the hook and bait together (Figure 14b). This is possibly
because the flesh of squid is firmer and more rubbery than fish, and turtles may
have difficulty biting off pieces of squid.
32
a)
Shank
Bend here (offset)
Eye
Eye
Offset
10
Point
33
Although there is a need for additional research, some studies have shown that
bait type and size can have an effect on sea turtle interactions. For example,
several studies have shown that turtle capture rates decreased when mackerel or
sardine was used as bait in longline fisheries instead of squid bait. It is
hypothesized that using larger bait may make it more difficult for turtles to swallow
the bait and, therefore, the hook. However, this remains to be tested.
Bycatch avoidance
method
Advantages
Disadvantages
Use of circle hooks
Use of fish bait
instead of squid bait
- Significant reductions
in sea turtle catch
rates as well as shark
catch rates
-
effect on economic
viability in some fisheries
May have an adverse
- Possible lower catch rates
of certain target and
commercially important
incidental species
- Possible increase in shark
catch rates
- Fishery-specific testing is
required to assess
efficacy, both for avoiding
turtles and to test
economic viability
- Significant reductions
in sea turtle catch
rates
- Significant reduction
in the proportion of
caught turtles that are
deeply hooked
- Possible higher catch
rates of swordfish
Summary of main advantages and disadvantages
of using circle hooks and fish bait in longline fisheries
Figure 14a. Fish bait is eaten in small bites
Figure 14b. Squid bait is gulped down whole
because of its firm and rubbery structure
Turtles usually occur at depths of less than 40 m
Several studies have shown that sea turtles spend the majority of their time at
depths of less than 40 m. For the most part, the diving behaviour of loggerhead
and olive ridley turtles is restricted to the upper 100 m of the water column and
although leatherbacks can dive much deeper – to 900 m – a large proportion of
their time is spent in the upper 200 m of the water column. The average dive
depth of leatherbacks is estimated to be 61.6 m and they forage at night on the
deep scattering layer (DSL) when it is nearer to the surface. The DSLs is a
concentrated layer of marine organisms found in most oceanic waters that
reflects and scatters sound waves, as from sonar. DSLs are of varying
composition and can include both plankton and nekton, i.e. free-swimming
organisms such as copepods, krill and small fish, and may occur at more than
one depth in the same location. Typically, they move upward at night to feed on
phytoplankton and downward during the day, as deep as 1 000 m, probably to
escape predators.
Although the depths at which turtles forage is generally known, empirical
evidence that demonstrates the effectiveness of setting longline gear deeper
to avoid interactions with turtles is currently lacking. This is a research priority.
However, there is evidence that deep-set longline fisheries have lower turtle
catch rates than shallow-set fisheries.
Deeper setting
The effect of deeper setting on the catch rate of target species in pelagic longline
fisheries is fishery-specific. For example, in certain fisheries it may not be
commercially viable to set gear deeper than 100 m, but for others, it will be feasible
to set gear deeper with no noticeable change in the catch rates of target species.
For example, tuna gear is typically set below turtle-abundant waters, while some
swordfish gear is likely to be set at depths where turtles are abundant.
In longline fisheries where it is economically viable to set gear deeper than 100 m,
a minimum precaution is for vessels to use longer branch lines adjacent to the
buoys; these are effectively the shallowest set hooks. An alternative is to leave a
gap on each side of the buoy line. Longliners should be encouraged to minimize
all gear between zero and 100 m to reduce the risk of entangling turtles. This can
be accomplished by increasing the length of buoy lines rather than having short
buoy lines and longer branch lines.
34
35
More turtles drown on deeper-set gear, but fewer turtles are caught
It is important to note that, although there is the potential for the interaction rate
with sea turtles to be much lower with deeper-set gear, the mortality rate of
turtles caught in deep-set gear is higher. Turtles caught in deep-set gear may
drown before the gear is hauled, whereas turtles caught in shallow-set gear are
typically alive when gear is retrieved.
Figure 15. Configuration of weighted gear with 20 hooks per basket and a target depth for the
shallowest hook of 120 m. Examples of possible target and bycatch species are shown: above 100
m these include sea turtles, sharks and some billfish while below 100 m they include bigeye tuna
and day-swimming broadbill swordfish. All baited hooks are below the 100 m line (after Beverly and
Robinson, 2004).
Three promising strategies have been developed to reduce the number of shallow
hooks in deep-set gear. One strategy uses lead weights and paired floats to
remove the entire fishing portion of the line out of the range of turtles. The second
uses a combination of lead weights and mid-water floats to standardize the depth
of branch lines (Figure 15). The third uses mid-water floats attached to the main
line to ensure that hooks are placed at the same depth, as opposed to having the
hooks suspended in a catenary curve.
Float
1st hook
120 m
Deepest hook
340 m
Depth
100 m
Lead weight
50 m
Setting longline
gear deeper than
turtle abundant
waters, i.e. deeper
than 100 m.
- May not be economically
viable for all longline
fisheries
- Turtles caught in deep-set
gear may drown before
gear is hauled
-
sea turtle interactions
(sea turtle bycatch
rates are higher by an
order of magnitude in
shallow-set pelagic
longline fisheries)
Substantially fewer
Summary of main advantages and disadvantages
of setting gear deeper than 100 m in longline fisheries
Bycatch avoidance
method
Advantages
Disadvantages
Dyed bait
Soak time
Bait that is dyed blue has not been shown to result in a significantly lower sea turtle
capture rate than untreated bait. This is based on research from longline fisheries
in the United States of America, Costa Rica and Japan, as well as on captive
green and loggerhead turtles. Furthermore, owing to the expense of dyeing bait
and given fishers' perceptions that dyeing bait is impractical, industry acceptance
of blue-dyed bait is expected to be low, unless competitively priced pre-dyed bait
becomes commercially available.
One study found the effect of total soak time (the period that fishing gear is in the
water) to have a highly significant effect on loggerhead catch rate. The effect of
daylight soak time was varied and inconclusive. Another study documented a
significant increase in loggerhead capture rate with increased length of daytime
line hauling. For leatherbacks, neither daylight nor total soak time had a significant
effect on leatherback catch rates. However, research with hook timers indicates
that leatherbacks are hooked more frequently at night. Overall, this limited body of
research suggests that reducing total soak time and daytime retrieval can reduce
loggerhead capture, while reducing the amount of time gear is in the water at night
might reduce leatherback catch rates.
36
37
Other gear technology strategies



Water temperature has been shown to play a role in sea turtle bycatch rates.
Pelagic longliners use an array of high-tech devices to locate the water
temperature “fronts” where the targeted fish congregate, attracted by high
prey concentrations. Longline vessel captains use satellite services that
provide sea surface and subsurface temperatures, weather faxes, GPS,
sonar and radar to help determine the best places and methods to set their
gear. It has been shown that loggerhead catch rates increased in sea surface
o
temperatures of greater than 22.2 C; leatherback catch rates increased in
o
sea surface temperatures above 20 C. One study reported that the highest
o
loggerhead catch rates occurred in water temperatures of 23.8 C. In contrast,
catch rates for target species showed a different trend. Higher swordfish
o
catches (by weight) occurred in water temperatures of below 20 C.
Therefore, for some fisheries, a promising strategy might be to fish in water
o
temperatures of less than 20 C. This might have the effect of decreasing sea
turtle interactions with longline fishing gear, while at the same time increasing
catch rates for target species.
Preliminary research indicates that single-hooked fish baits on circle
hooks may result in higher catch rates for swordfish – and a lower incidence
of loggerhead turtles swallowing the baited hook – than when the circle hook
is threaded through the fish bait multiple times. However, further studies are
required to test this method.
Turtles may be attracted to some types of light sticks, which are a standard
component in longline fisheries that target swordfish. They may also be
attracted to luminous beads or loop protectors that are used in some longline
fisheries. One study showed that the highest CPUE for leatherbacks in the
Atlantic longline fishery was on sets using light sticks. Another study showed
that the highest CPUE for loggerheads in the Canadian longline fishery was
on sets using luminous protectors. A study of captive loggerhead turtles found
that light sticks that flash intermittently did not attract loggerhead turtles.
A small commercial demonstration of “stealth” gear designed to be less
detectable by turtles included gear with:
light sticks shaded on the upper half;
light sticks with narrower light frequency;
counter-shaded floats (blue on the bottom half, orange on the top half);
dark grey lines;
dulled hardware (painted to remove the metallic shine).
It found that stealth gear was not economically viable in the Hawaiian longline
swordfish fishery.
Avoiding the use of conventional light sticks and other luminous fishing gear
would likely reduce sea turtle interaction rates. More investment in research and
the design of alternative light sticks is needed.





Longline gear modifications under development



A range of gear modifications have been tested to determine their impact on
the behaviour of captive turtles. For example, modifications to buoys; avoiding
the use of snaps (a clip used to attach the buoy to the line); the use of devices
like a funnel or soda bottle above or around the baited hook; and using various
colours, stiffnesses, and diameters of monofilament branch lines, have all
been tested. More research is needed to further develop these strategies.
Research into the development of a floatline that reduces the likelihood of
sea turtles becoming entangled in pelagic longline gear, is planned. The
concept for the tangle-free floatline is to construct the line using the same
material as conventional floatlines and, by using a combination of floats
and weights, ensure that the floatline is kept rigid.
Self-releasing hooks, which were developed for catch and release
fisheries for game fish such as salmon, may prove to be suitable for use in
longline fisheries, although no tests have yet been conducted.
Scientists are also testing methods to deter turtles from eating baited
hooks. These include acoustic deterrents and soaking bait in various
substances. One research group is attempting to identify shark
characteristics that produce avoidance behaviour in captive turtles.
However, to date the results of all these studies have been inconclusive.
38
39
Modifications to hooks and baits may reduce turtle capture, injury and death.
Artificial baits, both odourless and with fish odours, have been tested with a
view to identifying what attracts turtles to the hook. Other methods currently
under investigation include placing a device near or over the baited hook to
physically protect it from turtles. For example:
“Weedless” hooks have a device that covers the point of the hook and
which moves away when a fish bites the hook. Weedless hooks may be
effective at preventing the foul hooking of turtles.
“Whisker” hooks increase the dimension of a hook, making it more difficult
for a turtle to swallow.
“Smart” hooks have a device added to the hook that conceals the point at a
shallow depth or in warm sea temperatures, but which moves away from
the point when deployed at depth or in colder water. One way to rig a smart
hook might be to use a bimetallic strip to cover or expose the hook point
according to the temperature of the water in which it is deployed. Currently
under development is a modified circle hook to which a short, stiff piece of
wire is added, near to the eye of the hook, to increase the hook width,
making it more difficult for turtles to ingest. The wire points down at an
angle of about 45° to the hook's shank.



Further reading on sea turtle pelagic longline fisheries interactions
Balazs, G.H., Pooley, S.G. & Murakawa, S.K. 1995. Guidelines for handling marine
turtles hooked or entangled in the Hawaii longline fishery: results of an expert
workshop held in Honolulu, Hawaii, March 15–17, 1995. US Dept. Comm. NOAA
technical Memorandum NMFS, NOAA-TM-NMFS-SWFSC-222.
Bayliff, W.H., Moreno, J.I. & Majkowski, J., eds. 2005. Second Meeting of the Technical
Advisory Committee of the FAO Project "Management of Tuna Fishing Capacity:
Conservation and Socio-economics", Madrid, Spain, 15–18 March 2004. FAO
Fisheries Proceedings No. 2. Rome, FAO. 336 pp.
Beverly, S. 2003. Proposal for a deep setting technique for longline fishing to enhance
target CPUE and to avoid certain bycatch species. Standing Committee on Tuna and
Billfish, 16. Working Paper FTWG 9.
Beverly. S. & Chapman, L. 2007. Interactions between sea turtles and pelagic longline
fisheries, Scientific Committee, Third Regular Session, 13–24 August 2007, Hawaii,
USA. Palikir, Pohnpei, Federated States of Micronesia, Western and Central Pacific
Fisheries Commission.
Beverly, S. & Robinson, E. 2004. New deep setting longline technique for bycatch
mitigation. AFMA Report No. R03/1398. Noumea, Secretariat of the Pacific
Community.
Beverly, S., Robinson, E. & Itano, D. 2004. Trial setting of deep longline techniques to
reduce turtle bycatch and increase targeting of deep-swimming tunas. Standing
Committee on Tuna and Billfish, 17. Working Paper FTWG-7a. (also available at
www.spc.int/oceanfish/Html/SCTB/SCTB17/FTWG-7a.pdf).
Bolten, A. & Bjorndal, K. 2005. Experiment to evaluate gear modification on rates of sea
turtle bycatch in the swordfish longline fishery in the Azores Phase 4. Final Project
Report submitted to the National Marine Fisheries Service. Gainesville, USA, Archie
Carr Center for Sea Turtle Research, University of Florida.
Bolten, A.B., Martins, H.R. & Bjorndal, K.A., eds. 2000. Workshop to design and
experiment to determine the effects of longline gear modifications on sea turtle bycatch
rates. U.S. Dept. Comm. NOAA Tech, Memorandum NMFS-OPR-19.
Chaloupka, M., Parker, D. & Balazs, G. 2004. Modelling post-release mortality of
loggerhead sea turtles exposed to the Hawaii-based pelagic longline fishery. Marine
Ecology Progress Series, 280: 285–293.
Gilman, E. 2004. Catch fish not turtles using longlines. Educational pamphlet. Honolulu
(USA), Nairobi, and Bangkok, Blue Ocean Institute, United Nations Environment
Programme Regional Seas Programme, Western Pacific Regional Fishery
Management Council, and Indian Ocean – South-East Asian Marine Turtle MoU.
Gilman, E., Kobayashi, D., Swenarton, T., Brothers, N., Dalzell, P. & Kinan, I. 2007.
Reducing sea turtle interactions in the Hawaii-based longline swordfish fishery. Biol.
Cons., 139: 19–28.
Gilman, E, Zollett, E., Beverly, S., Nakano, H., Shiode, D., Davis, K.P., Dalzell, P. &
Kinan, I. 2006. Reducing sea turtle bycatch in pelagic longline gear. Fish and
Fisheries, 7(1): 2–23.
Hataway, D. & Mitchell, J. 2003. Report on gear evaluations to mitigate sea turtle capture
and mortality on pelagic longline using captive reared sea turtles. Pascagoula, USA,
U.S. National Marine Fisheries Service, Southeast Fisheries Science Center,
Mississippi Laboratories, Pascagoula Facility.
Javitech Ltd. 2002. Report on sea turtle interactions in the 2001 pelagic longline fishery.
Habitat Stewardship Program Canadian Wildlife Service, Environment Canada.
Javitech Ltd. 2003. Report on sea turtle interactions in the 2002 pelagic (offshore)
longline fishery. Habitat Stewardship Program Canadian Wildlife Service,
Environment Canada.
Kleiber, P. & Boggs, C. 2000. Workshop on reducing sea turtle takes in longline fisheries.
Miami, August 31 to September 1, 1999. 16 pp. (available at
http://pifsc.noaa.gov/adminrpts/2000–present/SWFC_Admin_Report_00-09.PDF).
Largacha, E., Parrales, M., Rendon, L., Velasquez, V., Orozco, M. & Hall, M. 2005.
Working with the Ecuadorian fishing community to reduce the mortality of sea turtles in
longlines: the first year March 2004 March 2005. Unpublished document. Honolulu,
USA, Western Pacific Regional Fishery Management Council. 57 pp.
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41
Laurent, L., Camiñas, J.A., Casale, P., Deflorio, M., de Metrio, G., Kapantagakis, A.,
Margaritoulis, D., Politou, C. & Valeiras, J. 2001. Assessing marine turtle bycatch in
European drifting longline and trawl fisheries for identifying fishing regulations. Project-
EC-DG Fisheries 98-008, Joint Project of BIOINSIGHT, IEO, IMBC, STPS, and
University of Bari. Villeurbanne, France.
Lewison, R.L., Freeman, S.A. & Crowder, L.B. 2004. Quantifying the effects of fisheries
on threatened species: the impact of pelagic longlines on loggerhead and leatherback
sea turtles. Ecol. Letters, 7(3): 221–231.
Løkkeborg, S. 2004. A review of existing and potential longline gear modifications to
reduce sea turtle mortality. In FAO, ed. Papers presented at the Expert Consultation on
Interactions Between Sea Turtles and Fisheries within an Ecosystem Context,
pp. 165–169. FAO Fisheries Report No. 738, Supplement. Rome, FAO. 238 pp.
Long, K. & Schroeder, B.A., eds. 2004. Proceedings of the International Workshop on
Marine Turtle Bycatch in Longline Fisheries. NOAA Technical Memorandum
NMFS-OPR-26.
Molony, B. 2005. Estimates of the mortality of non-target species with an initial focus on
seabirds, turtles and sharks. WCPFC-SC1 EB WP-1. 1st Meeting of the Scientific
Committee of the Western and Central Pacific Fisheries Commission, WCPFC-SC1,
Noumea, New Caledonia, 8–19 August 2005.
National Oceanic and Atmospheric Administration (NOAA). 2005. Technical
Assistance Workshop on Sea Turtle Bycatch Reduction Experiments in Longline
Fisheries. NOAA Fisheries Pacific Islands Fisheries Science Center (PIFSC).
Honolulu, Hawaii (USA), 11–14 April 2005. Unpublished.
Piovano, S., Di Marco, S., Dominici, A., Giacoma, C. & Zannetti, A. 2004. Loggerhead
(Caretta caretta) bycatches on longlines: the importance of olfactory stimuli. Ital. J.
Zool. Suppl., 2: 213–216.
Polovina, J., Balazs, G., Howell, E. & Parker, D. 2003. Dive-depth distribution of
loggerhead (Caretta caretta) and olive ridley (Lepidochelys olivacea) sea turtles in the
central North Pacific: Might deep longline sets catch fewer turtles? Fish. Bull., 101(1):
189–193.
Polovina, J.J., Kobayashi, D.R., Ellis, D.M., Seki, M.P., & Balazs, G.H. 2000. Turtles on
the edge: movement of loggerhead turtles (Caretta caretta) along oceanic fronts,
spanning longline fishing grounds in the central North Pacific, 1997–1998. Fish.
Oceanogr., 9: 71–82.
Ramirez, P. & Ania, L. 2000. Incidence of marine turtles in the Mexican long-line tuna
fishery in the Gulf of Mexico. NOAA Tech. Memo. NMFS-SEFSC-436. 110 pp.
Shiode, D., Hu, F., Shiga, M., Yokota, K. & Tokai, T. 2005. Mid-water float system for
standardizing hook depths on tuna longlines to reduce sea turtle bycatch. Fish. Sci.,
71: 1182–1184.
Secretariat of the Pacific Community (SPC). 2001. A review of turtle bycatch in the
western and central pacific ocean tuna fisheries: report prepared for the South Pacific
Regional Environment Programme by the Oceanic Fisheries Programme. Noumea,
New Caledonia.
Secretariat of the Pacific Community (SPC). 2005. Set your longline deep: catch more
target fish and avoid bycatch by using a new gear design. Noumea, New Caledonia.
Swimmer, Y. & Brill, R. 2001. Methods aimed to reduce marine turtle interactions with
longline gear. In 21st Annual Symposium on Sea Turtle Biology and Conservation.
Philadelphia, USA.
Swimmer, J., Brill, R. & Musyl, M. 2002. Use of pop-up satellite archival tags to quantify
mortality of marine turtles incidentally captured in longline fishing gear. Marine Turtle
Newsletter, 97: 3–7.
Watson, J., Foster, D., Epperly, S. & Shah A. 2004. Experiments in the Western Atlantic
Northeast distant waters to evaluate sea turtle mitigation measures in the pelagic
longline fishery. Report on experiments conducted in 2001 – 2003. Pascagoula, USA,
U.S. National Marine Fisheries Service.
Watson, J., Foster, D., Epperly, S. & Shah, A. 2005. Fishing methods to reduce sea turtle
mortality associated with pelagic longlines. Canadian Journal of Fisheries and Aquatic
Sciences, 62.
Williams, P., Anninos, P.J., Plotkin, P.T. & Salvini, K.L. 1996. Pelagic longline
fishery–sea turtle interactions: Proceedings of an industry, academic and government
experts, and stakeholders workshop held in Silver Springs, Maryland, 24–25 May
1994. NOAA Tech. Memorandum. NMFS-OPR-7.
Witzell, W.N. 1996. The incidental capture of sea turtles by the US pelagic longline fleet in
the western Atlantic Ocean. In P. Williams, P.J. Anninos, P.T. Plotkin & K.L. Salvini.
1996. Pelagic longline fishery-sea turtle interactions: Proceedings of an industry,
academic and government experts, and stakeholders workshop held in Silver Springs,
Maryland, 24–25 May 1994. NOAA Tech Memorandum. NMFS-OPR-7.
Witzell, W.N. 1999. Distribution and relative abundance of sea turtles caught incidentally
by the US pelagic longline fleet in the western North Atlantic Ocean 1992–1995. Fish.
Bull., 97:200–211.
Yokota, K., Kiyota, M. & Minami, H. 2006a. Shark catch in a pelagic longline fishery:
Comparison of circle and tuna hooks. Fish. Res., 81: 337–341.
Yokota, K., Minami, H. & Kiyota, M. 2006b. Measurement-points examination of circle
hooks for pelagic longline fishery to evaluate effects of hook design. Bull. Fish. Res.
Agen., 17: 83–102.
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43
The FAO encourages the use of TEDs and other measures that are comparable in
effectiveness, in shrimp trawl fisheries. In non-shrimp coastal trawl fisheries:
(i) data collection is encouraged in order to assess whether sea turtle interactions
are problematic; (ii) if necessary, research is encouraged to identify potential
methods for reducing sea turtle interactions and sea turtle mortality; and (iii) the
implementation of effective turtle avoidance methods that are identified by this
research is recommended.
The most common TED designs use an inclined grid to prevent large animals from
entering the codend. A guiding funnel/panel of netting in front of the grid may be
used to direct animals away from the escape opening and maximize the length of
grid available for separating large animals from the shrimp catch. Large animals
TEDs and BRDs work in coastal trawl fisheries
Fisheries that use bottom trawls in coastal waters and other near shore
areas – particularly coastal shrimp trawl fisheries – may have a high impact on
sea turtles. Considerable research in Australia, the United States of America
and later in several other developed and developing countries over more than
20 years has been conducted on gear modifications that reduce turtle bycatch.
This research resulted in the development of the turtle excluder device (TED),
which reduces the capture of sea turtles and other large animals including
sharks, stingrays, jellyfish and some large fish. Bycatch reduction devices
(BRDs) that reduce the bycatch of small fish have also been developed.
Important progress has been achieved, with empirical evidence showing that a
well-designed, properly installed and well maintained TED can exclude nearly
all sea turtles that enter a trawl, with an occasional turtle being caught only
immediately prior to gear hauling.
The use of TEDs became compulsory in the United States of America in 1989
and has subsequently been introduced to a number of developing and
developed countries, partly to enable these fisheries to meet United States
rules on shrimp imports.
Trawl fisheries
Trawl fisheries are perhaps in the most advanced stage as regards turtle
avoidance technologies. The turtle excluder device (TED) developed through a
close cooperation between scientists, fishing industry and fishery administration
led to a significant reduction in sea turtle bycatch.
Guiding funnel
Guiding
panel
Grid
Grid
Escape cover
Escape opening
and cover
Codend
Codend
Figure 16. The various components typically incorporated into the design of a downward-excluding
TED (top) and an upward-excluding TED (bottom)
are then guided by the grid toward an escape opening located either in the bottom
of the codend (Figure 16, upper) or in the top of the codend (Figure 16, lower).
Small animals (including shrimp) pass through the bars of the grid and enter the
codend. The escape opening is a hole cut in the codend and is usually covered
with a flap of netting or other material to prevent the escape of shrimp.
A less common TED design uses an inclined netting panel instead of a grid. The
netting guides large animals toward an escape opening in the top panel of the
trawl, while small animals pass through the meshes and enter the codend.
The appropriate design and size of a TED and other bycatch reduction devices
(BRDs) is fishery-specific. Several fishery-specific parameters for TED design
follow:
Size of the escape opening: The minimum size of the escape opening in
TEDs should be based on the length of turtles or other animals that are
encountered by a trawl fishery and that are considered to be unwanted
bycatch.

44
45




Grid orientation: The decision to use a grid that is oriented upwards or
downwards will depend on whether rocks, sponges and heavy debris are
present on the sea bed of the fishing grounds. Both orientations are equally
effective at excluding sea turtles. However, a downward-oriented grid is more
effective at excluding rocks, sponges and other debris. A bottom-excluding
TED allows the debris to roll towards the escape opening and be excluded,
while an upward-oriented grid does not allow these materials to be excluded.
TED grid size: Research in the United States of America and Australia has
demonstrated that larger grid sizes improve shrimp retention. This is because
a larger grid reduces clogging by increasing the sorting area of the grid.
Recent improvements in escape cover designs allow for larger grid sizes and
result in improved shrimp retention.
Grid angle: Experience from the United States of America and Australia has
demonstrated that a grid angle of 45–55° is optimal for both upward- and
downward-oriented grids. This angle ensures the effective avoidance of
turtles and other large animals and minimizes the loss of, and damage to,
shrimp. Regardless of the grid's orientation, an excessively high grid angle
delays the exclusion of turtles and increases the possibility that they will be
drowned. It may also result in blockage by rocks, sponges and other debris
and hamper the rapid passage of shrimp into the codend. Debris blockage
may also partially push the escape opening aside and cause shrimp loss. At
the opposite extreme, if the angle of the grid is too low, the escape cover may
not sit tightly over the escape opening and shrimp loss is likely to occur. A very
low grid angle may also cause the shape of the escape opening to become
distorted. However, low grid angles do not appear to affect the exclusion of
turtles from the trawl.
Bar spacing: Experience from the United States of America and Australia
has demonstrated that grid bar spacing of 100–120 mm for both upward- and
downward-oriented grids is optimal. This spacing ensures the effective
avoidance of turtles and other large animals and minimizes losses and
damage to shrimp. Grid bar spacing is important because it influences the
exclusion rate of small or juvenile turtles, as well as the passage of shrimp into
the codend. Bar spacing of greater than 120 mm is likely to increase the
potential for the head or flippers of large turtles to become fouled in the grid.
Smaller grid bar spacing, of less than 100 mm, will have a minimal effect on
turtle exclusion and may increase escape rates of fish and other animals.
However, it may also increase shrimp loss.
TEDs are sold commercially
Various TED designs have been developed and are commercially available.
Each has a different shape, size, bar interval and installation angle. In most
countries with an important shrimp trawl fishery, like Australia and the United
States of America use and design of TEDs are regulated by law.





Guiding panels or funnels: Some TED designs include guiding panels or
funnels of netting ahead of the grid. These are usually constructed from
netting material and are designed to guide shrimp away from the escape
opening. However, most Australian and United States trawl shrimp fishers
have decided not to use these funnels, and there has been little change in
shrimp catches.
Netting escape cover: Most TED designs include a netting escape cover
over the escape opening. These are used in all bottom-excluding grids and
most top-excluding grids. They help to prevent shrimp from escaping.
Grid material: Grids are typically constructed of aluminium or stainless steel
rod or tubing. The latter is preferred in large grids because it provides
additional strength and less weight.
Grid shape: The shape of a grid usually fits into one of three categories;
rectangular, oval, or a hybrid rectangular and oval grid (”tombstone” grid).
Rectangular grids are the simplest to construct and provide a relative large
escape opening. A disadvantage of this shape is the risk of netting abrasion at
the corners of the grid. Oval grids better conform to the cylindrical shape of the
codend and the problem of net abrasion is reduced. Oval grids may also
increase the ability of an escape cover to seal tightly over the escape opening
and prevent shrimp loss. Tombstone grids can be used so that the square end
of the grid provides for a wide escape opening while the opposing rounded end
of the grid better conforms to the shape of the codend. In this way, the grid
provides a good compromise between rectangular and oval grids.
Floats: Typically, several floats are attached to TEDs to provide buoyancy
and stability. This is especially necessary for TEDs with large, heavy grids.
Floats are also useful when the gear is at the sea surface because they
provide an indication of the orientation of the grid prior to deployment.
46
47
No safety hazard
Hard TEDs have been criticized because they were thought to pose a safety
hazard to fishing crews, particularly in rough weather. However, these fears
have proved to be largely unfounded, if the TED is installed in the right place.
Figure 17. Examples of different grids
Hard TEDs
A schematic diagram of the “Super Shooter” TED, an example of a hard TED with
a rigid grid is represented in Figure 16. Originally developed for use in the Gulf of
Mexico and southwestern Atlantic shrimp fisheries, the Super Shooter also has
been tested in the Australian shrimp fishery. The grid has an oval shape and is
constructed from aluminium rod or pipe. The bars of the grid are bent near the
escape opening to facilitate the removal of weed that may foul the bars and
prevent the entry of shrimp into the codend. (Although a guiding panel is shown in
Figures 16 and 17, it is not used in current designs because of clogging. In the
United States of America a guiding panel is now prohibited because it restricts the
escape of larger turtles.) Large animals are then guided by the bars towards the
escape opening in the bottom of the codend. These animals then push aside a
cover located over the escape opening and are excluded from the trawl net. Small
animals exit the guiding panel, pass through the bars and into the codend. The
escape cover sits tightly against the escape opening and prevents the escape of
small animals.
Soft TEDs use a non-rigid inclined panel of netting to guide bycatch towards the
escape opening in the top of the trawl. Examples of this TED include the Morrison
TED (Figure 18), the Parker TED and the “blubber” chute. Soft TEDs have been
found to be less effective in excluding heavy sponges and other seabed animals
because these foul the netting. Soft TEDs have also been problematic in
maintaining turtle exclusion efficiency. The Parker TED is now the only soft TED
approved for use in the Gulf of Mexico and southwestern Atlantic shrimp fisheries.
The Parker TED does not use the slack, large-mesh webbing that is known to
cause turtle entanglements in previously approved soft TEDs. Instead, the Parker
TED consists of a single triangular panel, composed of webbing of two different
mesh sizes that forms a barrier for turtles inside a trawl and that angles toward an
escape opening in the top of the trawl. The Parker TED was tested in a variety of
trawl sizes and styles. During testing, the Parker TED successfully excluded
100 percent of the turtles introduced into the trawl, and is especially adaptable
under certain environmental conditions; shrimp loss was approximately 9 percent.
Soft TEDs
48
Figure 18. The Morrison TED, an example of a soft TED (after Eayrs, 2007)
49
- Very large escape opening may
allow large leatherback turtles
and other large animals to be
rapidly excluded
- Exclude some sea bed animals
(sponges, corals, etc.) and rocks
(downward-excluding TEDs only)
- May increase shrimp catch due
to longer towing time (less drag
and fewer hauls)
- May reduce sorting time
- May improve shrimp quality by
reducing contact with large
animals
- Reduce hazard to crews from
large, dangerous animals
-
the guiding panel or funnel by
large animals and debris could
lead to shrimp loss
- Fouling of escape opening by
large animals and debris could
lead to shrimp loss (a.k.a. TEDed)
- A little more difficult to handle
than a standard codend
- Rigid grid may be a safety hazard
to crew (depends on location in
codend)
Damage, fouling or clogging of
- Poor installation may affect trawl
performance
- Damage, fouling or clogging of
the guiding panel by large
animals and debris could lead to
shrimp loss
- Effectiveness depends on trawl
spread
- More difficult to repair than a
standard trawl
- Less effective than hard TEDs at
excluding heavy items such as
rocks and sponges
- Very large escape opening may
allow large leatherback turtles
and other large animals to be
rapidly excluded
- May increase shrimp catch due
to longer towing time (less drag
and fewer hauls)
- May reduce sorting time
- May improve shrimp quality by
reducing contact with large
animals
- Reduce hazard to crews from
large, dangerous animals
Hard TEDs
Soft TEDs
Advantages
Disadvantages
50
TED performance and efficiency are influenced by different combinations of
design and construction. An overview of factors influencing TED efficiency are
presented in Figure 19.
TED EFFICIENCY
escape
opening
escape
covers
f larg
o
e
n
a
o
i
n
s
im
u
l
a
c
x
ls
E
R
h
e
c
t
t
e
a
n
c
tio
p
n
m
i
o
r
f
h
th s
e
bar
spacing
grid
shape
grid size
guiding
pannel or
funnel
bent
bars
grid
material
grid
orientation
flotation
backwash
funnels
grid
angle
Figure 19. Factors influencing TED efficiency
In addition to reducing unwanted bycatch of fish, sea turtles, sponges and
jellyfish, TEDs provide direct operational benefits to trawl shrimp fisheries by:
(i)
reducing catch sorting times;
(ii) reducing damage to shrimp by sharks, stingrays and other large fish
species, thereby improving the value of the target catch; and
(iii) enhancing the safety of fishing crews by removing stingrays and sharks
from the catch.
Future research and development may well identify superior turtle avoidance
methods for trawl gear. There is consensus that contact with a TED and
subsequent exclusion does little harm to sea turtles, providing the TED is well
maintained and escape occurs quickly. However, what is not well understood is
whether there are long-term adverse effects from repeated exclusion of an
individual turtle over a short period. It is unclear to what extent escape from a trawl
may be delayed by a poorly designed or installed TED without causing severe