Report 3 (of 6): Fishing
for Change
GILL
NETS
A
gill net is a special kind of fishing net comprising
a long length of fibre (cotton or nylon etc.) meshes.
It may be set on the sea bottom, surface or midwater
(figure 1) and is usually left overnight.
It
may be anchored or freefloating. To be effective,
a net should not be detectable to the fish. The
bottom of the net is generally weighted while the
top is supported by floats (figure 2). There are
also other ways of "rigging" the net
without weights or floats.
A
fish, swimming into the net, can only pass part
way through before becoming trapped. The twine
of the net should have enough elasticity to allow
the fish to swim through the mesh until it is firmly
caught. As the fish struggles to free itself, it
becomes "gilled" as the net twine slips
into the back of its gill making it impossible
for the fish to move either forward or backward.
According
to the desired size of fish, the mesh size is varied.
Fish with a smaller girth than that of the mesh
opening are able to swim through. A large mesh
size, e.g. 230mm to 300mm, can be used for larger
fish, such as sharks or tuna, and a small mesh
size, e.g. 153mm to 178mm, can be used for smaller
fish. The way the net is constructed and the depth
it is set also determines the size and species
of fish captured.
Gill
Net Operations
Setting
gill nets may involve using a marker buoy with
a rope (buoyline) and anchor attached to one end
of the net. These are are thrown into the sea from
the stern of the boat. As the net flows out into
the water, the floatline and sinkerline are arranged
so as to ensure that the net does not tangle.
When
the gill net is taken from the water, it is generally
the buoyline and anchor that are hauled in first.
The crew then haul in the net using the float and
sinkerlines, removing and collecting the fish which
are caught in the mesh.
Net
Braiding and Rigging
Braiding
the term for net making, may be done by machine
or by hand. Any size of mesh can be braided.
Rigging
is the process of attaching ropes, floats, weights
and other accessories to the net to make it ready
for fishing. Rigging is very important because
it determines the shape of the meshes. way the
netting is hung from the floatline and sinkerline
determines the shape of all meshes in the net.
The staples (loops of twine) that connect the netting
with the head rope should be exactly the same distance
apart so that all the meshes have the same shape.
Materials
required for making a gill net include ropes, twine,
floats, sinkers, buoys, anchor, netting needles,
knives, and mesh gauges. Two fixed posts, for example,
trees, are required to secure the head rope while
the braiding is carried out.
All
netting, twine and ropes are generally made of
synthetic fibres which tend to be more durable
than natural materials. However, floats and sinkers
are often made from local materials such as bamboo,
wood, bottles, or stones.
Floats
and Sinkers
The
purpose of the floats in a gill net is to ensure
the buoyancy of the floatline (head rope) is correct.
They must be strong enough to withstand heavy pressure
in deep waters and must not absorb water or become
entangled in the netting. Therefore, the shape,
size and materials of the floats is crucial. They
are usually attached directly to the floatline
or threaded onto it.
Sinkers
(weights) are fastened to the sinkerline (foot
rope) and must have sufficient weight to sink the
bottom part of the fishing net. They must also
be smooth to ensure that they do not become entangled
in the netting. The number of floats and sinkers
and the distance between them depends on the type
of fishing method being used, or whether the net
is a surface, midwater or bottom set net. The type
of material used in the gill net, the buoyancy
of the floats and the weight of the sinkers will
also affect the number of floats and sinkers required
for the gill net and the efficiency with which
a net will catch fish.
Buoys
Surface
buoys (generally called marker buoys) should have
enough buoyancy to prevent the nets from sinking
even with heavy catches and be large enough to
be seen from a distance.
Types
of Knots
Various
kinds of knots are used for joining ropes and lengths
of net together. The kind of knot used will depend
on the type of rope (material, width etc.); the
use of the knot (i.e. for attaching to the anchor,
buoy or other nets etc.); whether the knot should
slip; or whether the knot is permanent.
Netting
Needles
A
special kind of needle (figure 4) is used for making
nets by hand. It may be made of wood
,
bone, plastic or metal and comes in different sizes
to suit the size of the mesh. The use of netting
needles is essential for net making and repair.
Mesh
Gauge
For
hand made nets, a mesh gauge (or mesh stick) is
used to determine the mesh size and ensure uniformity.
This is usually made from a piece of hard smooth
wood which is either flat or rounded.
Selection
of Mesh Size A mesh is composed of four knots and four bars (figure
5). It must be the right size for the target
species of fish. Knowledge and experience of
fishing is essential for selecting the right
mesh size.
Double
Selvedging
After
the completion of net braiding, the head rope and
foot rope bottom are strengthened by a technique
called "double selvedging". Thicker twine
or mesh made of double twine is used, to ensure
that it is strong enough to withstand the forces
against it while at sea (figure 6).
How
to start Net Braiding
To
start net braiding (figure 7), a number of loops
need to be formed, using a clove hitch, on the
head rope which will be equivalent to the number
of meshes required. This is known as the setting
up row. When forming the setting up row the proportion
of twine used for the knots is slightly more than
the amount used in making the ordinary sheet bend.
A smaller mesh gauge is necessary for making the
initial row of loops.
Net
Mending
In
order to repair tears, needles with either single
or double twine should be used depending on the
kind of net pieces to be mended and these pieces
should be hung squarely so that the meshes are
even. The meshes and bars made during net mending
must be the same length as the original meshes
of the net.
When
the tear needs too much braiding to sew up the
sides, the repair can be made by replacing the
damaged portion of the net by a patch of netting
of the same mesh size. In order to avoid complicating
the work, the hole prepared should be square or
rectangular, without any bars, like the patch itself.
If bars are left in the hole, the patch has to
have the same number, in the same places, so that
they can be connected.
For
further information, please contact:
Clive
Radcliffe University of Lincolnshire and Humberside
61 Bargate Grimsby North East Lincolnshire DN34
5AA ENGLAND
Tel./Fax:
+00 44 (0) 172 348827
Acknowledgement
is given to the International Committee of the
Red Cross ICRC who provided the information for the project.
References:
Fisheries
Technologies for Developing Countries: (National
Academy Press) ISBN-0-309-03788-3
Mending
of Fishing Nets: L.Libert and A.Maucorps (FAO)
ISBN-0-85238-062-3
Rope,
Twine and Net Making: A.Sanctuary (Shire Publications
Ltd) ISBN-0-85263-502-8
Further
Reading
(T)Fishermans
Workbook (A)J Prado (D)ISBN 0852381638, ,1990 (Fishing
News Books) £14.99
(T)A
Livelihood from Fishing: Globalization and sustainable
fisheries policies (A)Alain Le Sann (B)Fish constitutes
a limited - and jeopardized - natural resource.
Yet, in order to meet expanding demand from consumers
and, consequently, industry, developed countries
import ever increasing volumes of fish. While decommissioned
vessels from Northern fleets are being transferred
to the South to alleviate pressure on depleted
European stocks, countries in the South are exporting
more and more sea products to the North. In these
conditions, how are the food requirements of impoverished
populations, for whom fish is a vital source of
protein, going to be met? The author argues that
solutions do exist, although they entail a number
of conditions: the sharing of resources, protection
of the environment, implementation of measures
for responsible fisheries, and integrated aquaculture.
In addition, in order to develop an integrated
form of aquaculture, the rights of fishworkers
must be reinforced, since government policies bent
on modernization and protection of natural resources
often lead to their marginalization. This book,
based on over ten years' involvement with fishworkers'
associations in the North and South, provides an
overview of fisheries and makes proposals for the
integration of social aspects in a new fishing
policy. It will be of interest to all those who
are keen to develop their environmental awareness
and are concerned about the welfare of fishworkers.
(D)ISBN 1853393983, 130pp,1998 (ITP) £8.95
To
order these books please write to: ITDG Development
Bookshop, 103-105 Southampton Row, London, WC1B
4HH, UK. Tel: +44 (0) 171 436 9761 Fax: +44 (0)
171 436 2013 or visit our website at ITDG
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