FPT – 321

FISHING GEAR TECHNOLOGY

DR.VIPUL GUPTAASSTT. PROFESSOR

FISH PROCESSING TECHNOLOGY

FISHING GEAR MATERIAL• Two types : 1. Natural

2. Synthetic• Efficiency of a fishing gear is dependent on materials used for its construction• Natural fibers get decomposed by cellulose digesting bacteria so life is less• Advantages of synthetic material

– Rot resistance– Durability– Stronger– Do not absorb water– No preservative required– Better productivity– Better catching efficiency

• Netting (as per ISO)Netting is a meshed structure of indefinite shape and size, composed of

one yarn or one or more systems of yarns joined or interlaced.• Fiber

Basic material for construction of fishing gear. It is a unit of matter of hair like dimensions whose length is atleast 200 times greater than its width.

• Most popularly used synthetic materials Polyamide, Polyester, Polyethylene, Polypropylene

Based on the source from which the fibers are obtained they are classified as 1. Natural fibers2. Synthetic fibers

NATURAL FIBERS

1. Vegetable fibers (obtained from plants) - cellulose base & are prone to rotting in water as they are attacked by cellulose digesting micro-organisms.

Seed fiber e.g. Cotton (cotton plant)

Bast fiber (soft fibers) e.g. Ramie (China grass), Hemp (Cannabis sativa), Linen

Leaf fiber (hard fibers) e.g. Manila (Abaca plant), Sisal (Agava sisalana)

Fruit fiber e.g. coir (husk of coconut plant)

2. Animal fibers (obtained from animals) – protein base

e.g. Wool, Hair and Silk. Out of these only silk is used in fishing gears.

SYNTHETIC FIBERS: These are man made fibers manufactured by chemical synthesis of

simple substances like phenol, benzene, acetylene, prussic acid etc.

Poly-condensation compounds

(Water is eliminated)

Poly-meric compounds

(water is not eliminated)

Poly-additive compounds(Monomers)

Mixed Polymer compounds

• Poly-amide (PA)• Nylon• Amilan• Perlon• Kapron

• Poly-ester (PES)• Terylene• Dacron

• Poly-vinyl Alcohol (PVAA)

• Poly-vinyl Chloride (PVC)

(First synthetic fiber used for fishing)

• Poly-ethylene (PE)

• Poly-propylene (PP)

• Poly-vinylidine Chloride (PVD)

(Mixed polymers are formed by

co-polymerization of mixture of vinylidine and vinyl alcohol)

Most popularly used synthetic materialsPolyamide, Polyester, Polyethylene and Polypropylene

1. Continuous filament –

(e.g. PA, PES, PP)

2. Staple fibers (e.g. PA, PES)

3. Mono filaments (e.g. PE)

4. Split fibers (e.g. PP)

BASIC FIBER FORMS Synthetic fibers may be produced in one or more of basic forms

Tests carried out for testing the fiber yarn1. Water test only PE and PP will float2. Visual inspection by experience like colour, texture3. Burning test by gas production / reaction taking place /

residue4. Solubility test in different of chemicals5. Melting point test especially to distinguish PE and PP

- Strongest

- indefinite length & run the entire length of yarn

- silky in texture

- thinner than natural silk

- Made by cutting filaments

- Short length (40 - 120 mm)

- Less visible

- larger diameter (0.1 – 1.0 mm or more)

- made from longitudinally split plastic tapes

Physical properties • Density• Breaking strength / load

• Tenacity• Tensile strength

• Breaking length• Elastic properties

• Extensibility• Extension at break • Elastic recovery

• Water absorption• Shrinkage• Abrasion resistance• Weather resistance• Sinking speed• Visibility• Melting point• Flammability• Towing resistance

Chemical properties

Effect of chemicals such as

• Acids

• Alkalis

• Oils

• Preservatives

Biological properties

Damage caused by the organisms like

• Fungi

• Fouler

• Bacteria etc.

It is essential to know the properties of different types of fibers prior to their selection for construction of fishing gears.

PROPERTIES OF FIBERS

Chemical properties

• It is the property of a material to withstand the effect of chemicals such as acids, alkalis, oils and preservatives which may damage the materials.

• Natural fibres have a poor resistance to acids.

Biological properties

• It is the quality of netting materials to withstand the damage caused by the organisms like Fungi, Fouler and Bacteria.

• Vegetable fibres are prone to quicker rotting whereas synthetic fibre have good resistance.

Density: Density is the mass per unit volume and is expressed as grams per

cubic centimeter (g/cm3). Fibres of low densities (<1.00 g/cm3) like PE and PP float in water and hence hold more weight. The sinking speed of the netting will increase with the increase in density of material. This property of the fibers is of significance in the construction of certain gears like the surrounding nets etc.. The density of cotton is more than many synthetic fibre materials, among the synthetic materials. PVD has the highest density of 1.70 followed by PES 1.38 and PA 1.14.

Breaking strength / breaking load Breaking strength is the maximum force applied to a specimen causing

it to rupture or break. It is expressed in kilogram-force (kgf). Special machines known as breaking strength testers or dynamometers are used for determining the breaking strength. It is expressed in terms of tenacity and tensile strength,

Tenacity: It is the breaking strength per unit denier measured as T (gm/ den)

Tensile strength: It is the breaking strength per unit area and is expressed as kg/mm2

For fishing net twines the wet strength is more relevant as they are used in water. The wet strength is determined by keeping the specimen in water for 12 hours and testing it immediately thereafter. Both PA and PVAA lose strength in wet condition whereas PES, PE and PP remain unaffected.

Breaking length: This is the calculated length of a specimen the mass of which is equal

to its breaking strength and is expressed in km. Breaking length (km) = Breaking load in kg

Weight in g/m The breaking length can be converted into tenacity

Breaking length (km) = 9 x Tenacity (gm/den)

Elastic properties: Elasticity is the property of a material by virtue of which it tends to

recover its original length and shape after removal of the stress-causing elongation. Extensibility and elastic recovery are part of the elastic properties. Extensibility: This is the property of a material to undergo extension or elongation under the influence of a force. Extension at break: This is the total extension at break. It is expressed as a percentage of initial length. Extension at break = Length at break - Initial length

Initial lengthPE, PP and PVAA have more extension at break followed by PA and

PES. The extension in wet condition increases in PA and PVAA whereas it remains unchanged in the case of other synthetic materials. Elastic recovery: The ability to recover elongation is called elasticity. PA has exceptionally high elastic property, i.e. 98%.

X 100

Water absorption This is the property of netting materials to absorb water when immersed

in water and is expressed as a percentage of dry weight. Materials, especially natural fibres like cotton absorbing more water, pose difficulty in handling. PE and PP do not absorb water at all whereas PA, PES and PVAA absorb a little water.

ShrinkageThis is the reduction in length of a material induced by wetting or any

other treatment like setting. Shrinkage is not a major problem in synthetic fibres.

Abrasion resistanceThis is the resistance of a material to the wear off of the whole or any

part of it when rubbed against a surface. The abrasion resistance of vegetable fibres is comparatively less. Staple fibres show lower resistance to abrasion than continuous filaments.

Weather resistanceThis is the property of netting materials to withstand the effect of

atmospheric conditions. It is a combined effect of light, rain, wind, industrial smoke and gases. Natural fibres are more weather resistant than the synthetic ones. The rate of deterioration due to weather conditions is measured by the decrease in breaking strength.

Sinking speed: This is the speed at which the material sinks through the water. It is

important for certain types of gears like purse seines.

Visibility: It is the quality of the netting materials to be seen in water during

operation. This property is of more relevance in certain gears like gill nets. Vegetable fibres gather dirt over them and become visible whereas tile synthetic fibres are less visible. Among them, monofilaments are invisible due to their transparent nature.

Melting point: This is the property of heat resistance of the material. The melting point

along with shrinkage need to be considered while dying the nets in hot dye bath. PA and PES are more heat resistant than other materials.

Flammability: It is the property of material to burn in flame. Natural fibres are highly

combustible whereas synthetic fibres have varying degrees of flammability. PA and PVAA melt faster while PES, PE and PP burn slower.

Towing resistance: It is the resistance offered by netting while being towed through the

water. This property is important in the design of gears like trawls and seine nets. Synthetic material have less towing resistance.

Chemical properties

It is the property of a material to withstand the effect of chemicals such as acids, alkalis, oils and preservatives which may damage the materials. Natural fibres have a poor resistance to acids.

Biological properties

It is the quality of netting materials to withstand the damage caused by the organisms like Fungi, Fouler and Bacteria. Vegetable fibres are prone to quicker rotting whereas synthetic fibre have good resistance.

CONSTRUCTION OF NETTING YARN• Netting yarn is the standardized universal term for all textile

material which is suitable for the manufacture of netting for fishing nets and which may be directly knitted into netting by machine or by hand, without having to undergo further process.

• There are three main types of netting yarns: (a) Twisted netting yarn (b) Braided netting yarn (c) Knotless netting yarn

of these, twisted netting yarn is more commonly used in fishing

CONSTRUCTION OF TWISTED NETTING YARN: The basic material for the construction of twisted netting

is single yarn. Single yarn is the simplest continuous thread composed of fibers. Two or more single yarns are twisted together to form netting twine or folded yarn. The netting yarns used in fishing undergo a further twisting operation, i.e. two or more folded yarns are twisted to form a cabled yarn or cabled netting twine. The twist given to the folded and cabled yarns are in opposite directions.

CONSTRUCTION OF CABLED NETTING YARN

CONSTRUCTION OF BRAIDED NETTING YARN: • Braiding is the process of interlacing three or more threads so

that they cross each other and are laid together in diagonal formation. Braiding is also called as plaiting.

• The braided yarn is in the form of a tube and consists of – Core, – Single yarns & – Strands

• The braiding machine consists of spindles, half of them moving in left direction and the other half in right direction. This enables the strands of one set of spindles to pass alternately over and under one or more of the strands of the other set of spindles.

• Core is the central part used to fill up the space inside the braided tube. It may be made out of a single yarn, folded yarn or mono filaments. The core increases the weight of yarn and, therefore, for fishing nets, braids without core are preferred. These are also softer and have better knot stability.

• The number of strands are determined by the number of spindles in the machine. Commonly 6, 8, 12 and 16 strands are used. The single yarns are either not twisted or twisted together to form strands. These strands are interlaced

CONSTRUCTION OF BRAIDED NETTING YARN

CONSTRUCTION OF KNOTLESS NETTING YARN: In knotless netting, single yarns are interlaced at the joints and the netting is made in only one working process. There are three types of knotless netting:

a. Japanese twisted knotless netting . b. Knotless Raschel netting c. Braided knotless netting

Merits of knotless netting yarn• Knotless netting is light and compact• It is easier to handle due to its less bulk.• Production costs are lower due to considerable saving of

material.• It offers less towing resistance.• It has high abrasion resistance.• It has more constant and accurate mesh size.• It is easier to clean and quick to dry as dirt does not

accumulate on the netting.

TWIST • The twist is the spiral disposition of the components of a single yarn, folded

yarn or netting yarn. • The amount of twist is the number of turns per unit of length, i.e. t/m (turns

per meter).• Depending on the amount of twist given, the twines are classified as

• Soft twist• Medium twist• Hard twist• Extra hard twist

• The amount of twist given to the twines is decided as per the requirements of specific fishing gears.

• For gill nets and seines, soft and medium twists are used• Hard twists are used in trawls.• Extra hard in lines and ropes.• In the twisting operations, the direction of twist in succeeding operation is

opposite to that of the preceding operation.• Depending on the direction of twist, they are classified as ‘S’ twist & ‘Z’ twist.• ‘S’ twist is when the spiral formed by the fibers or filaments incline in the

same direction as the central portion of the letter ‘S’.• When the spirals incline in the direction as the central portion of the letter ‘Z’

and the product is held vertically, it is called ‘Z’ twist.

DESIGNATION OF NETTING YARNS or YARN-NUMBERING SYSTEM : The system indicating the size or thickness of the basic yarn is termed as yarn-numbering system. The yarn number or the count is essential in the purchase and selection of netting yarns.There are different methods of designating the yarn count or number.

1. Direct system 2. Indirect system.

DIRECT SYSTEM: The yarn number is expressed in terms of mass per unit length. There are two methods of numbering the yarn under direct system:DENIER SYSTEM : This is the most commonly used system for denoting the size of yarn. It is the weight in gram of 9000 m of a single yarn. The symbol used to designate denier is “Td', 'Den' or 'D'. The most commonly used nylon yarn for netting twines is 210 denier which means that 9000 m of a single yarn weighs 210 g.TEX SYSTEM: It is international numbering system recommended by ISO. It is the weight in gram of 1000 m of a single yarn. 'Tex' is the symbol used for this system.

In both the systems, as the count increases, the thickness of the yarn also increases.

INDIRECT SYSTEM

The yarn number is expressed in terms of length per unit mass. There are three types under indirect system.

Metric system: It is the length of a single yarn the weight of which is one kg. The symbol used is 'Nm'.

British system: This gives the number of hanks, each measuring 840 yards in a unit mass of one English pound (lb). It is represented by the symbol 'Ne'.

840 yards of a single yarn weigh 1 lb = 1 Ne

840 x 20 yards of a single yarn weigh 1 Ib = 20 Ne

Runnage system: This system is used in the purchase of finished twine and rope. It indicates the length per unit weight and the units are m/kg, yards/lb. and feet/lb.

Conversion formula of various systems

Since different systems are in use in different countries, a conversion formula to convert one system into another has been evolved, viz.

Tex = 590.5 = 1000 = 0.111 Td

Ne Nm

DESIGNATION OF NETING YARNS AND ROPESComplete designation of netting yarn in tex system The following aspects are to be given: (i) Tex value of a single yarn(ii) Number of single yarns in the first fold(iii) Number of folded yarns in the finished product(iv) R tex value of the finished product(v) Final twist direction of the finished productThe first three aspects are joined by a multiplication sign (x), while the fourth one is to be separated from the preceding part by a semicolon(;)Example: Cable yarn = 23 tex x 4 x 3 ; R 320 tex x Z

Folded yarn = 23 tex x 3 ; 75 tex ZThis means that the count number of the basic yarn is 23 tex, 4

such yarns are twisted to form a netting twine and 3 such netting twines are twisted to form the cabled twine. R is the resultant tex and is 320 and Z is the outer twist of the twine. Brief designation in tex systemThis gives only the resultant linear density with the direction of twist of the outer fold, e.g. R 320 tex Z. This is mainly used for braided netting yarn and netting yarns composed of dissimilar materials or yarns.

British count(i) British count of a single yarn(ii) Number of single yarns in folded yarn(iii) Number of folded yarns in cabled yarnThe above three are joined by strokes: 20 Ne/2/3 This is mainly used in specifying the cotton twines.Denier count(i) Denier count of a single yarn(ii) Number of single yarns in folded yarn(iii) Number of folded yarns in cabled yarnThe above three are joined by strokes: 210/2/3Code number This specifies the number of single yarns in a folded yarn and ex-pressed in numbers. This is only used occasionally to specify cotton and nylon twines.Example Code No. Corresponding cotton Corresponding nylon

specifications (British) specifications (Denier) 1/2 20/1/2 210/1/21 20/1/3 210/1/31½ 20/2/2 210/2/22 20/2/3 210/2/33 20/3/3 210/3/320 20/20/3 210/20/3

Diameter : This is given in millimeters (mm) and is used to specify the

following twines and ropes : 1. Monofilament twines2. Manila twines3. Sisal twines4. Steel wire ropes5. Fibre ropes

CircumferenceThis is often used in mm to specify the fibre ropes.

ROPESA rope is defined as a cordage with circumference of 25 mm or more.Ropes are extensively used in the fishing gear construction and operation. They provide the frame work and linear strengthening components in the fabrication of fishing net such as gill nets, trammel nets, seines and trawl nets and constitute main line and buoy lines of large long lines. Fibre materials used are Polyamide (PA), Polyester (PES), Polypropylene (PP), Polyethylene (PE), Polyvinyl alcohol (PVAA), Manila, Sisal, Coir, Hemp and Steel wire.

CONSTRUCTION OF ROPES•Ropes generally consists of three or more strands, cabled or braided together, with or with out core with a finished diameter of not less than 4 mm (circumference 25 mm). Base on construction, ropes are grouped into laid and braided. In the laid rope, fibers are twisted into rope yarn and two or more rope yarns are twisted in the opposite direction to produce strands.

•Three or four strands are laid in the direction opposite to the twist of strands to produce the laid rope. 3 strand construction is the most commonly used & it is called hawser laid or plain laid rope. Depending on the no. of twists per unit length, hard, medium and soft laid ropes are available. A four strand construction is called shroud laid rope.

•Three or more laid ropes are combined by twisting in the opposite direction, to produce cable laid ropes. In the braided construction, strands are plaited together to produce different types of braided ropes.

• FIBRE ROPES: Fibre ropes are widely used for framing and strengthening of fishing gears and also as warps, bridles and sweeps in small scale trawling operation. Fibre ropes are vulnerable to stretch.

Steel wire ropes

Steel wire ropes are widely used as trawl warps, sweeps and bridles and as foot rope and head rope in large trawl nets, as purse wire in purse seines. Steel wire ropes have high breaking strength and resistance to sustain loading with low elongation, unlike fibre ropes. Steel wire ropes are however stiff and heavy.

Combination ropes

Combination ropes or combined rope with or without a central core is manufactured by twisting strands which are formed from a combination of natural or synthetic fibre yarns and steel wires. In this construction steel wires are completely covered by fibre yarns.

The steel wires provide high breaking strength and low extensibility while fibre component reduces stiffness and protects the steel wires from wear and tear. Polypropylene is the most widely used fibre material in combination ropes. Combination ropes are used in the construction of large bottom and mid water trawls and as sweeps and bridles.

FLOATS• The floats are essential components of fishing gears and are used

– to keep the fishing gear at the desired position (required depth), – obtaining proper shape during operation, – maintaining vertical opening in gears etc.

• Desired properties for the floats used in fishing• should be able to withstand the water pressure• should be highly buoyant• should not absorb water• must be light in weight• durable / long service life• should have means of attachment

• In trawls floats are used along the headline to keep the mouth of the net open vertically and maintain the fishing height

• In gillnets they are used along the headline to keep the wall of netting vertically and also to maintain the fishing position in the water column by means of buoy lines.

• In purse seines and seine nets they are used to keep the netting vertically, close to the sea surface.

• In long lines they are used to keep the lines in the desired depth of operation.

CLASSIFICATION OF FLOATS

• The floats can be differentiated based on – density (i.e. high or low density material), – material used for construction (i.e……..), – pressure they can withstand – surface floats or deep sea floats.

• Low density material floats

Wood : • Used in indigenous fishing especially for gill nets• Easily available • Relatively cheap• Absorb water on prolonged usage• Crack on drying

Cork :• Mostly used in surface gill nets• Easily available• Highly buoyant• Cannot stand rough handling• Absorb water on continuous operation• Not very strong

Low density material floats

Thermocole : (expanded polystyrene)• Mainly used for gill nets and seines• Very high buoyancy • Very light• Do not absorb water• Cannot withstand the pressure

Sponge plastic : (PVC)• Mainly used for gill nets and seines• Light• Do not rot• Do not absorb water• Pressure resistance is poor

Synthetic rubber :• Low water absorption• High buoyancy which is not lost by continuous operation• Easy storage• Possibility of moulding into any shape• Cannot withstand the pressure

High density material floatsGlass :

– They are made in the form of spheres which are covered by netting to facilitate fixing and protection. But this increases the resistance while towing.

– Do not absorb water– Can withstand the pressure up to 400 m.

Aluminium :– They are made in two halves and are welded at the seam– Mainly used in trawls and some times in gill nets and seines– Can withstand the pressure up to 80 m.– More buoyant than glass floats

Steel :– They are made in two halves and are welded at the seam – These are not very popular– Buoyancy is reduced due to thick wall– Rust gets accumulated

High Density Plastic :– Useful in deep water trawls– Can be used up to a depth of 250 m.– No corrosion problem

GRP :– Not readily available– Costly– Highly buoyant– Can with stand pressure up to the depth of 400 m.

BUOYS• The buoy is a floating mark used for the different purposes like:

Navigation (marking channels and approaches) Marking fishing grounds Locating the fishing gear in operation For keeping the fishing gear at the required depth

• The buoy is attached to the fishing gear by the buoy line. • Empty water-tight tins, wooden barrels, bigger floats made of

glass, aluminium & plastic are commonly used as buoys.• Apart from these, special type of buoys are used in gill net and

long line fishing. They are light buoy, radio buoy & Dahn buoy.Dahn buoy: Dahn buoys are set when locations of good fish

concentration are found. • It consists of :-

(i) a pole with a ballast at the bottom, float in the middle and a flag, light and radar reflector at the upper end; (ii) a buoy or drum; and (iii) an anchor and anchor rope.

• Dahn buoy is used in set gill nets as well as in Danish seine.

Dahn Buoy

LIGHT BUOYS: These are battery-operated buoys used to locate tuna long line gear at night. They are attached at regular distances on the line. Light buoy consists of two water-tight chambers, the lower one containing dry battery and the upper one has a 3-5 watt bulb. The bulb remains above the water.

RADIO BUOYS: The range of radio buoys is about 50 km much more than the light buoys. They are also used to locate the tuna long line gear. It consists of a transistorized transmitter. One type gives continuous signals and the other one intermittent signals. The signals are picked up by the receiver in the vessel.

SINKERS• The sinkers are essential components of fishing gear. • They are used

• to keep the net in the desired position as in gill nets • to keep a trawl open vertically • to stretch the net downwards to increase the sinking

speed in a purse seine. • The materials used for sinkers are clay, cement, granite

stone, iron and lead. • Occasionally materials like copper alloy, brass, iron and

porcelain are also used. • The sinkers should have

• high sinking force or under water weight • high specific gravity • should be durable• easily available

• The specific gravity of Lead is 11.3 and Iron is 7.9.

ANCHORS• Anchor is a large and heavy instrument designed to hold or retain the

ship in any desired locality at sea by chaining it to the sea bottom and prevent her from drifting due to the action of wind, tide & current.

• It is also used to secure fishing gear in satisfactory position at sea.• Anchors are essential especially in case of engine failures or rudder

breakdown. • Anchors are helpful in sailing boats when wind is not favourable. • Stones, wood tied with stones, iron and cement concrete or steel are

used as materials for the anchors.Parts of anchor

An anchor consists of a ring which is used to attach the warp. There is a shank connecting the arms to the anchor ring. The terminal part of the shank connecting the arms is called the crown. Arms are the curved parts with flukes at their terminals. The triangular structures at the end of the arms which dig into the bottom are called the flukes. Sharp ends of the flukes are called bills or points.

A horizontal cross piece situated at the top of the shank helps to turn the anchor when it hits the bottom enabling the flukes to dig into the bottom and is called the stock. The anchor is handled in and out of the boat by means of a gravity band.

TYPES OF ANCHORSThere are five types of anchors currently in use in fishing gears:

Admirality: The admirality has very good holding power especially when a

chain is used as cable. It has two flukes & a stock at right angle. It is also known as fishermen's anchor. Since it takes a lot of space for stowage.Danforth:

This anchor is an American design having the advantage of stowage on the deck. It consists of two broad flukes set close together with a stock passing through the crown.CQR:

It is a stockless anchor used only in small vessels. It is also known as plough anchor. It has good holding power. The fluke has the shape of a plough set back to back and is held to the shank by a pin.Patent:

This is also a stockless anchor. The two arms can move about 45° on either side of shank. Tripping palm on tripping horn is fitted to the arm which help the flukes to dig into the ground. Patent anchor is easy to handle and to stow and is mainly used in large vessels.Grapnel:

This is a five-pronged stockless anchor and has very good holding power. However, stowage is the main problem

Fisherman’s / AdmiralityBill or Point a

CQR

Grapnel

Danforth Patent

HOOKS :• The fish hooks are used in line fishing. • Hooks are made of galvanized or aluminum coated

iron, brass, or stainless steel. They are manufactured in different shapes & sizes.

• The hooks are specified by different methods. The Norwegian method of numbering hooks is followed in India. In this method, the size of hook becomes smaller as the number increases.

• A simple fish hook generally consists of a head by which it is connected to the line, shank, bend, point and barb.

• Hooks without barbs / barb less hooks are used in tuna pole and line fishing.

• Double/ triple hooks are also used to reduce the chances of fish to escape as the fish is hooked at two different positions. They are used in troll lines.

Structure of a hook

Fish jigs

JIGS :Jigs or artificial baits are used for

attracting the fishes either by their shape, colour or by their reflection. The materials used are tin, lead, brass, whalebone, feathers, plastic fishes, etc.

The squid jigs have a single or double whorl of barb less hooks around suitably shaped and coloured plastic or metal body.

5. TRAPSIn this method, fish enters the trap voluntarily either for food or shelter but is prevented from coming out by means of certain arrangements.5.1 Hiding Places: Certain fishes like eels, octopus and crabs have the habit of hiding among branches of trees, bundles of twigs, hollow bamboo reeds, etc. Sometimes these are baited to lure the fish. They are then hauled up and the hiding fishes removed. Strictly these are not true traps.5.2 Barriers: Barriers like walls or dams made of stones, mud, netting or split bamboo pieces are used to trap the fish during tides. In water where there are no currents, fences are provided to guide the fish into pockets. These are then removed by means of other gears. In rivers where there are strong currents, the fishes are guided on to a slanting screen of gratings constructed in the river and ascending in the direction of the current. The fishes are caught when the water disappears through the screen. The migrating fishes are best caught in a watched catching chamber which is a large chamber open on three sides. These require constant watch so as to close the entrance as soon as the fish enters. This is normally done by pulling up the netting from the bottom thus trapping the fish.

5.3 Mechanical traps: These are similar to mouse traps where the victim itself releases a mechanism which prevents its escape. In gravity traps, weight is suspended which when released by the fish prevents its escape. The elastic power of a bent rod is made use of in bent rod traps. In torsion traps, the strength of twisted twine is used to close the trap.5.4 Tubular traps: There are long tubes without valves. They are narrow and the fish are held in the tubes by their fins or there are thorn-lined traps where the inside of the trap has been fastened with thorny twigs hindering the escape of fish.5.5 Basket traps: These traps mostly have small entrance and are made of wood, wire, netting, plastic, etc. Fyke nets are made of netting and are normally used in shallow water. These traps consist of cylindrical or cone-shaped bags mounted on rings and are provided with wings or leaders which guide the fish towards the opening of bags.5.6 Trap nets: These are large uncovered gears anchored or fixed on stakes, set or floating with various types of fish herding and retaining devices. Weirs are made of wood and pound nets are made of netting. The pound nets are mostly divided into chambers closed at the bottom by netting.

6. AERIAL TRAPS.6.1 Box traps: Salmon box traps are well known in the salmon fisheries of the northern Europe. The salmon jump over the obstacle and find themselves in a box trap which is provided with a roof at the other end so that they cannot escape.6.2 Raft traps: Raft either moored or drifting are considered to be obstacles by the mullets and they are caught in the raft while trying to escape from it. To prevent the escape of fish from the raft either the edges of the raft are bent upwards or their surface is covered with twigs6.3 Boat traps: Boat traps are used in several countries for catching jumping fish. The fishes while trying to jump over an obstacle find themselves in the boat which is held at an angle.6.4 Verandah nets: These are popular nets in Mediterranean, China, India and some parts of Africa. Verandah nets consist of two parts - a vertical barrier netting and a horizontal verandah for collecting fishes. These nets can be operated either as movable ones or as stationary.6.5 Scoop nets for jumping fish: flying fish are caught in scoop nets directly from the air or this is like fishing in the air. A display of torch lights is used to attract the fish towards the surface and they are caught in the scoop nets as they fly through the air.

7. BAGNET: In bag nets, the fishes enter voluntarily and are caught by filtering. They are kept open vertically by a totally or partially framed mouth and horizontally by the current.7.1 Scoop net: These are small bag nets operated by hand and are moved through the water, i.e. the fishes are caught by the scooping action. They are variously shaped. Landing nets have almost round frame. Skimming nets are triangular nets. Push nets have triangular or semicircular frame pushed by hand or operated from boats.7.2 Scrape net: In these nets, fishes are caught by skimming. They are large framed bag nets operated with the help of a lever over the edge of a boat or on the bank of a river.7.3 Gape net without wings: They are large bag nets without wings set either on stakes in shallower waters or on anchors when operated from deeper waters. They are popularly used in rivers where currents are strong. They may or may not have frames and are stretched between a series of stakes. They are also called stow nets. 7.4 Gape net with wings: These are bag nets with wings which are either fixed on stakes or on anchors. In some cases, one end of these nets is connected to the bank and the other to a large otter board to keep the mouth open instead of using a frame. Wings act as a guiding device directing the fish into the bag net.

8. DRAGGED GEARThis group includes active gears which are towed through

water and manner of their capture is by filtration. The nets are towed either near the bottom or in the pelagic region for an unlimited time. Included in this category are trawls and dredges.8.1 Dredges: These are dragged along the bottom to collect mollusks such as mussels, oysters, scallops, clams, etc. The gear consists of a conical-shaped net with a rigid frame in front. They are of varying weight and size and are operated from shore or from boat.8.2 Sweep trawls: Sheets of webbing made of single or triple walls are towed over the bottom.8.3 Bottom trawls: Conical-shaped nets are towed over the bottom. The mouth of the net is kept open by means of either beam, otter boards or two boats pulling apart.8.4 Midwater trawls: This is a trawl net operated in the pelagic region either from a single or two boats.

9. SEINE NETS

The manner of capture is to surround an area of water with a

long net with or without a bag at the centre. Two long ropes are

tied to the ends of the net which help in herding the fish as well

as their hauling. The gear is towed over the area with both ends

fixed to a point on the shore or on a vessel.

9.1 Double stick nets: These are winged bags of netting held

between two sticks. They are more popular with river fishermen.

They are held in river currents; then encircled and there upon

the catch is lifted out from water.

9.2 Genuine seine nets: This category includes beach seines

and boat seines. Beach seines are operated from the shore and

are generally used in shallow waters. They may or may not

have bag in the centre. These are gears for bulk fishery. Boat

seines are operated from the boat.

10. SURROUNDING NETSThese nets surround the fish not only from the sides but also from the bottom. Included in this category are Lampara nets, ring nets and purse seines.10.1 Lampara nets: This gear is shaped like a dust pan. The central bent portion is in the form of a spoon and there are two lateral wings. There is no purse line underneath. After encircling the shoal, the foot rope is pulled preventing the escape of fish. Mesh size varies in different parts of net. The ground rope is shorted than the head rope.10.2 Purse seines: These are surrounding gears provided with a purse line at the bottom which when pulled through the purse rings close the bottom of the gear thus preventing the escape of fish. It can be operated from a single or from two boats. Mostly, a single boat makes use of a skiff for its operation.10.3 Ring nets: They are shaped like a purse seine but unlike purse seines the netting has different mesh sizes and ground rope is shorted than the head rope. It is a hybrid type between Lampara & purse seine. It is used for small schools of fish in shallow waters up to 40 m depth and are generally operated by a single small boat or low powered vessel. They are lighter to handle, cheaper to build and faster in operation. These are not popularly operated in India.