Various bycatch issues in Indian demersal trawl fisheries

1. WEST BENGAL University OF ANIMAL AND FISHERY SCIENCES
FACULTY OF FISHERY SCIENCES
PRW – 421 & SEM- 421
THE ISSUE OF BYCATCH IN INDIAN’S DEMERSAL
TRAWL FISHERIES
SUBMITTED TO:
Prof. N. A. Talwar
DEPT. OF FEG
SUBMITTED BY :
Abdul Hannan Mondal
B. F. Sc. 4th Yr 2nd
Sem.
FS- F/2016/01

2. THE ISSUE OF BYCATCH IN
INDIAN’S DEMERSAL TRAWL
FISHERIES

3. Introduction
• Many fisheries are non-selective fishing gear
catching animals that they did not intend to. This
non-target extra catch is known as ‘by-catch’.
• Of these by-catch species, some have a commercial
value and are brought back to land by fishers to be
sold.
• However, a large proportion is unwanted and so is
discarded thrown back over the side of the boat.
• Nearly 20 percent of shark species are threatened
with extinction, primarily as a result of being caught
accidentally on long lines. By-catch also includes
young fish that could rebuild populations if they
were allowed to grow and breed.

4. • FAO estimates: 7.3 million tones of fish is discarded
every year.
• Not only fish:
Hundreds of thousands of sea turtles, seabirds and
marine mammals, including whales, dolphins and
porpoises , die as by-catch.
As many as 200,000 logger
head sea turtles and 50,000
leatherback sea turtles
are caught annually. Long
line fishing also kills hundreds
of thousands of seabirds when
they become entangled in drift nets or caught on
long line hooks when they dive for bait.

5. By catch is the portion of
the catch that is not
comprised of the fishery’s
target species . Species that
are caught accidentally
By-catch from a shrimp trawler

6. • The FAO defines discards as
the portion of the catch that is thrown back into the sea either
dead or alive . Like marine mammals , crustaceans , and seabirds
,sharks, birds, turtles, corals ,etc.

7. Results
 Waste of a natural resource without any economic returns.
 Major threat to the health of fish stocks .
 Threat to the future of the fishing industry .
 Capture and discarding juvenile lower catch opportunities for
those species in the future.
-Negative impact on the marine ecosystem &
biodiversity
-Decrease The sustainability of fisheries
By-catch also includes sponges and
rocks and may reduce the quality
of the shrimp catch

8. Solution
1. Use and development of species selective gear.
2. Monitoring and control of fishing gears
3. Motivating Technical conservation measures to improve
gear selectivity.
4. Use Electronic logbooks (assessing discard rates during
routine inspection by fishery inspectorate officers. )
5. The use of closed areas or protected areas to protect
juvenile and spawning fish.
6. Fisheries management &marketing strategies
7. State’s laws for prohibiting discards & over grading.
Sustainable development

9. fishermen have been using fishing methods designed to
reduce the capture of many of these animals, including :
• ground chain arrangements that reduce the amount of seabed
animals, rocks and debris taken,
• avoidance of fishing grounds where by-catch is known to be high,
including grounds where coral, sponges and rocks are present,
• using mesh sizes big enough to allow some small animals to
escape.
• using TEDs and BRDs.

10. TEDs
Used to exclude turtles and
other large animals from the
trawl

11. 'turtle excluder device' is any modification to a shrimp trawl
designed to reduce the capture of turtles. These devices are
sometimes called a 'trawl efficiency device' because they can also
prevent the capture of other large animals including sharks,
stingrays, jellyfish and some large fish.

12. JTED
• Juvenile and Trash Excluder Device
Filters small fish including trash fish from the catch but not the
larger shrimp.

14. RES Radial Escape Section
BRD features a guiding funnel to concentrate all animals into the
middle of the cod end. As fish exit the funnel, some swim forward
and through a panel of large square-meshes that extend radically
around the cod end.

15. Square Cod-end Mesh to Reduce By-catch
• Demersal trawls are used throughout the world and account for
almost a quarter of the global landed marine catch .
• Trawls retain large ratios of incidental (i.e. by catch) to targeted
catches.
• That is because of their active fishing mechanisms, the frequent
use of small diamond-shaped mesh
Trawling is a method of fishing
that involves pulling a fishing net
through the water behind one or
more boats.
The boats that are used for
trawling are called trawlers or
draggers .

16. square-mesh cod end
• square-mesh netting stays open for the duration of the tow,
unlike diamond-mesh netting that closes under the weight of the
catch. The selection of mesh size is very important and trial and
error is needed to find the mesh size that maximizes fish
exclusion.
Effects of Square and Diamond Mesh

17. • Can square-mesh cod-ends help reduce by-
catch?
• The mesh openings of a traditional diamond-mesh cod-end
collapse as it fills with catch and prevents the escape of small fish.
The mesh openings of a square-mesh cod-end retain their shape
as it fills with catch and are available for fish to escape.

18. Square-mesh cod-ends
• Advantages:
1. Small fish by-catch may escape
2. May reduce sorting times
3. May increase towing time (less drag and fewer hauls)
4. May increase shrimp catch due to longer towing time
5. Less reliant on behavior and swimming ability to exclude small fish and
animals.
• Disadvantages:
1. Shape of fish affects escape rates, so some species are more likely to
escape than others
2. Relatively difficult to construct. particularly a combined diamond- and
square-mesh cod end .
3. Square-meshes may distort if not correctly attached to a diamond-
mesh netting
4. More difficult to repair than traditional diamond-mesh.

19. • What is a square-mesh window and how might
it reduce by-catch?
• A square-mesh window is usually a panel of square mesh netting
located in the top panel of the cod end or trawl body.
• As fish pass through the trawl they orientate direction toward the
device and swim through the square escape openings.

20.  Another way to reduce by-catch
Dan Watson devised a system based on a series of escape rings
for fish – which can be fitted to a fisherman's trawler net won a
prestigious international award for creating a "humane" net to
make fishing more sustainable by preventing small fish.

21. Fishing net with emergency exits
• The net is designed to make commercial fishing more sustainable by
reducing the number of non-target and juvenile fish picked up by
trawlers, Watson explained to the BBC that about 20 rings are needed
per net, costing a total of around $800 .Rs. ~ 48000
• Advancing science, reducing by-catch :
In conservation, finding the balance between research and action is an
ever-present challenge; the price of a mistake could be species
extinction, the inefficient use of limited conservation funds, or
unnecessary constraints on resource use.

22. Contribution of trawl
landing at important trawl
landing

23. Fisheye
• It is designed to allow strong swimming fish to escape from the
trawl.

24. square-mesh window
It is simply a panel of large meshes hung on the bar so they
remain open during the tow .This is in contrast to diamond
meshes which tend to close under tension.

26. • A key to the successful involvement of fishermen is to explore
how they may benefit from reducing by-catch.
These benefits may include:
1. improved trawling and processing efficiency.
2. better product quality and marketing
opportunities, and
3. protecting the marine environment
and extending the life of the fishery.
4. The catch on the right includes large
animals because a TED was not fitted
to the trawl. The catch on the left is
the result of using a TED.

27. What are the population-level effects on by-
catch species?
As a result of the challenges associated
with estimating demographic parameters
for sea turtles, seabirds, and marine
mammals, we know relatively little about
where or for which species the effects of
by-catch pose the greatest threat to
population viability This knowledge gap
poses important dilemmas for natural
resource managers. Without a clear indication of whether an
observed level of by-catch is unsustainable, it may be difficult to
spur adequate conservation action where it is needed. Alternatively,
where wildlife conservation is an important management priority,
uncertainty about the population impacts of by-catch could lead to
unnecessary conservation actions.

28. • How can by-catch of threatened species be
reduced?
The study of by-catch mitigation efforts can be divided into 4
related categories: species ecology and behavior, by-catch
mitigation techniques and technologies, the social and legal
framework that surround efforts to reduce by-catch, and post-
implementation monitoring. A better understanding of the
behavior and ecology of the species involved may help reduce
by-catch encounters. South wood et al. (2008) review auditory,
chemical, and light-based methods for reducing sea turtle by-
catch in long line fisheries, focusing on the detection abilities of
pelagic fishes and sea turtles. Based on existing knowledge, they
argue that visual (and, to a lesser degree, chemical) cues are the
most effective venue for future research.

29.  Which fisheries and gear types result in the
highest by-catch of marine mega fauna?
• By-catch research has mostly targeted industrial fisheries, overlooking the
potential effects of small-scale artisanal fisheries on threatened species.
While understandable from a logistic point of view (i.e. it is much easier to
study a few large ships than many small boats), this restricted focus will no
longer suffice. A growing body of evidence documents high by-catch of
threatened species by artisanal fisheries.
 Which threatened species are taken as by-
catch?
• The diversity of species affected by by-catch is still largely unknown in
many parts of the world . Many of these knowledge gaps can be
attributed to a lack of taxonomic expertise and research funding, as is
the case for many developing nations where basic lists of species that
occur or are caught by fishers are incomplete. Other factors, such as
conservation status and policy-related mandates also play a role in
shaping the imbalance of our knowledge across.

30. Conclusion
The impacts of trawling on the marine ecosystem, though
relatively well researched in temperate waters and reported
to hamper the marine ecosystem, remains poorly studied in
the tropical waters. In countries like India, the absence of
benchmark data on the quantity and quality of by-catch and
lack of information on the biology and ecosystem roles of by-
catch species coupled with methodological limitations such as
absence of control sites or sites protected from trawling,
handicap defining strategies and policies aimed at reducing
by-catch. However, for ensuring sustainability of oceanic
resources. we need to have a precautionary approach which
envisages reducing by-catch rather than efforts to fully utilize
the by-catch.

31. References
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