- Square mesh codends can help reduce bycatch compared to traditional diamond mesh codends. Square mesh retains its shape as the codend fills, leaving openings for small fish to escape. Studies show square mesh codends of 55-60mm reduced bycatch by 22-33% and juveniles by up to 95% compared to 100mm diamond mesh. - Another bycatch reduction method is using a square mesh window in the top of the codend or trawl body. As fish pass through the trawl they orient towards the device and can escape through the square openings. - Bycatch reduction devices like Dan Watson's design of escape rings fitted along trawl nets can also make trawling more sustainable by allowing non

1. Square Cod-end Mesh to
Reduce By-catch

2. Introduction
 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

3.  Trawling is a method of fishing that involves pulling
a fishing net through the water behind one or more
boats….
 Trawl fisheries sector account more than 50% of
the marine fisheries production of India.
 The boats that are used for trawling are
called trawlers or draggers
 The net that is used for trawling is called a trawl
 In Karnataka, bottom trawling was first introduced by
the Japanese trawler M.S. Maru in 1961. (Kurup et al., 1987)
Trawling

5. An Overview

6.  The use of the term “L V F” varies from country to
country
 One category of LVF are those not used for direct
human consumption, which may be either landed
and discarded at the sea itself.
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L V F

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TRASH FISH

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Discards are that portion of the total catch which is dumped
or thrown overboard at sea.” (FAO).
What is a discard ?
•Discards are generally considered a waste of fish resources and inconsistent with
responsible fisheries.

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10.  The estimated landing of low value bycatch (LVB) in trawl
fisheries, increased from 14 % in 2008 to 25 % in 2011
At Mangalore:
 An estimated 25,067 t of LVB valued at Rs. 25 crores was landed by multiday
trawlers (MDF) at Mangalore Fisheries Harbour.
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CMFRI, 2011
Landing of LVB
The high demand for trash fish has been the major reason for
increased landing.
A. P. Dineshbabu (30 Jan 2014)

11. A global problem
 The FAO has recently estimated that nearly 7 million
tonnes of fish by-catch is discarded globally by
commercial fishermen every year.
 This is equivalent to about 8% of the global catch
from marine capture fisheries.
 Industrial shrimp trawling in the capture of by-catch and
accounts for about 27% of all global discards.

12. Estimations of Low value/Trash fish production in
Asia-Pacific (tonnes)
Country Low
value/trash
fish
% of total
catch
Dominant gear Year of
estimation
Bangladesh 71 000 17% Gill nets (48%)
Non-mechanised
set bags (42%)
2001-2002
China 5 316 000 38% Trawl 2001
India 271 000 10-20% Trawl 2003
Viet Nam 933 183 36% Trawl 2001
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FAO 2005

13.  Although the overall design of a trawl influences
the type and quantity of catch that enters the gear,
 Selection is largely determined by
 (i) the lateral mesh openings in the cod end, and
 (ii) the probability that these are encountered
 Towards achieving desired selection in otter trawls
is to regulate a suitable mesh size in the codends.

14. Performance of square-
mesh codends
 The performance of square-mesh codends was examined as a discard
and by-catch reduction device for the Shark, scallop etc. trawl fishery.
 Of the three different-sized square-mesh codends (50, 55, 60 mm) tested
against the standard 100-mm diamond-mesh codends,
 The 50-mm square-mesh codends performed poorly with relatively high
retention of small (<85 mm shell height) scallops,
 Whereas the 55- and 60-mm square-mesh codends retained 22–33% less
smaller scallops than did the diamond-mesh codends.

15.  Overall, a mean of 5% loss in commercial-sized scallops across all
three square-mesh codends and significant by-catch reductions of up
to 95% were achieved compared with the diamond mesh.
 Catch rate of prawns by the square-mesh codend was less than 2% of
that of the standard prawn net.
 The performance of the 60-mm square-mesh codend presents a good
basis for its use in commercial trials in the Shark Bay scallop trawl
fishery.
 A move to square-mesh codends could result in a significant
reduction of small scallops and by-catch and may potentially increase
the catches of commercial-sized scallops as a result in improvements in
water flow and net efficiency.

16. Effects of Square and
Diamond Mesh

18. Asia-Pacific Fishery Commission
 The demand for targeted resources has paved way for
indiscriminate bottom trawling along the coast with an
ultimate result of massive wastage of low value, high
volume by-catch including a wide spectrum of non-edible
benthic biota.
 The small cod end mesh of bottom trawlers has also
exploited juveniles and sub-adults of commercial species
in large quantities.

19. Global response to reduce
bycatch
 In response to concerns over the capture of turtles and
other bycatch in shrimp trawls, fishermen in many
countries have taken steps to modify the trawl net and use
bycatch reduction devices.

20. Can square-mesh codends
help reduce bycatch?
The mesh openings of a traditional diamond-mesh codend collapse as it fills with
catch and prevents the escape of small fish.
The mesh openings of a square-mesh codend retain their shape as it fills with catch
and are available for fish to escape.

22. What is a square-mesh
window and how might it
reduce bycatch?
A square-mesh window is usually a panel of square mesh netting located in the top panel of
the codend or trawl body.
As fish pass through the trawl they orientate directionally toward the device and swim through
the square escape openings.

23. 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
Designed by: Dan Watson
Thursday 8 Nov 2 01 2
Source: www.guardian.co.uk/environment/2012/nov/08/humane-fishing-net-dyson-award
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Another way to reduce bycatch

24. 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
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26. Close Season
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Fishing Holiday

27. Karnataka 1986
Marine Fisheries Regulation Act

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