Classifications

• • A—HUMAN NECESSITIES
  • A01—AGRICULTURE; FORESTRY; ANIMAL HUSBANDRY; HUNTING; TRAPPING; FISHING
  • A01K—ANIMAL HUSBANDRY; AVICULTURE; APICULTURE; PISCICULTURE; FISHING; REARING OR BREEDING ANIMALS, NOT OTHERWISE PROVIDED FOR; NEW BREEDS OF ANIMALS
  • A01K73/00—Drawn nets
  • A01K73/02—Trawling nets
  • A01K73/04—Devices for spreading or positioning, e.g. control thereof
• • A—HUMAN NECESSITIES
  • A01—AGRICULTURE; FORESTRY; ANIMAL HUSBANDRY; HUNTING; TRAPPING; FISHING
  • A01K—ANIMAL HUSBANDRY; AVICULTURE; APICULTURE; PISCICULTURE; FISHING; REARING OR BREEDING ANIMALS, NOT OTHERWISE PROVIDED FOR; NEW BREEDS OF ANIMALS
  • A01K73/00—Drawn nets
  • A01K73/02—Trawling nets

Definitions

• the invention relates to fishing tackle, especially the fish catch-bag, a so-calle cod-end, in a fishing trawl, and of the kind where the towing direction of the trawl runs diagonally through the net meshes, and wherein there is in ⁇ serted a special sorting part which, to a higher degree than the remaining part, is arranged to maintain the shape of the openings through which the fish which are required to be sorted out by said openings shall pass.
• the tech ⁇ nical preservation measures include standards for the mesh sizes of the nets, standards for how large a proportion of the haul may comprise incidental catch, and regulations concerning the minimum size of the fish and shellfish caught in the nets.
• the object of the standards regarding the mesh size is to avoid the landing of fish under a certain size. It is as ⁇ sumed that the mesh has a size-sorting effect, which solely involves the mesh size in relation to the size of the fish. Therefore, efforts are made to achieve a size-sorting which may also serve as a kind of species sorting by adjusting the mesh to whatever kind of fish it is desired to catch. Fish which are smaller than the permissible minimum size can escape from the net. It is important that the fish are not damaged by being sorted through the mesh.
• the hypo- thesis behind the rules for mesh size is that the larger the mesh of the net, the greater the number and the size of fish permitted to escape, thus remaining part of the fish population and utilizing their potential of growth. How ⁇ ever, the mesh size has proved to be a very unreliable ba ⁇ sis for the estimation of the sorting abilities of the fi ⁇ shing tackle, and herewith the user's possibilities of ful ⁇ filling the current regulations regarding minimum size and incidental catch.
• the stretch mesh size i.e. the inner dimensions of an ex ⁇ tended mesh
• the shape of the mesh can vary from quadratic to dia ⁇ mond-shaped to a narrow slot, where the length of the slot corresponds more or less to the so-called stretch mesh size.
• the shape of the mesh is determined by the towing forces which influence the mesh during use, and herewith by the net's construction and conditions of use, and it is precisely these circumstances that explain the poor selec ⁇ tivity and the high death-rate in the incidental catch.
• the death-rate is due to the fish in the trawl becoming so exhausted and suffering so much physical damage that they die either as a direct result of the damage, or later be ⁇ cause the damage they have suffered makes it difficult for them to get food. Their exhaustion increases with the time they spend in the trawl, and the damages are worsened with the difficulty of getting through the meshes and out of the net.
• the catch-bag With the normal trawl design, the catch-bag has a mesh opening which is down at approx. 10% of the mesh length, because the towing force in the longitudinal direction cau- ses the meshes to close. Consequently, there is no possibi ⁇ lity of escape for other than fish of very small dimen- sions.
• the object of the present invention is to achieve a very high degree of selectivity, e.g. when fishing with a trawl or seine-net.
• a second object is to ensure that the fish sorted-out are treated carefully during their passage in and out of the net, and thus have the possibility of survi- val and to form the basis for future catches.
• a third ob ⁇ ject is to produce fishing tackle where the size-sorting element can be delivered as a unit which can be incorpo ⁇ rated into the tackle produced by the local net maker in accordance with the requirements and wishes of the indivi- dual users, but where the unit is produced in such a manner that users, authorities and competitors can be assured that the equipment in use has the prescribed characteris ⁇ tics with regard to selectivity and the ability to retain lawful catches.
• a construction is known whereby a sorting plate of firm ma ⁇ terial is inserted in or just in front of the trawl bag, this being able to absorb compressive stresses so that the sorting holes can retain their size, but it has proved that this stiff construction gives rise to handling problems. Moreover, the sorting ability is limited, the reason being that the sorting plate can be mounted only on a short part of the trawl bag.
• the ability of the net to sort the fish is further limited, in that it has been found that the extent of load relief varies so that the relieved net undulates and flaps, and this movement de- ters a large part of the undesired catch from seeking a way out through the mesh.
• the object of the present invention is thus to provide a solution to the problem of sorting to be found with the existing fishing tackles. It is also the object to show how a commonly known catch-bag can be made selective throughout the whole of its length, to present a sorting part for in ⁇ corporation into known bags and a net material for use in said sorting part.
• the catch-bag according to the invention is peculiar in that the sorting part is made up of one or more pieces of net which are arranged to retain the shape and the size of their meshes, and which are mounted in the catch-bag.
• the invention will be illustrated with a trawl as an examp- le, but what is described can be used with the same advan ⁇ tages on other fishing tackle which comprises a catch-bag.
• the catch-bag is the rearmost end of the trawl and consists of a longitudinally extended bag. Its diameter, length and mesh size will depend of the desired species of fish, bot- torn conditions, size of boat etc.
• a catch-bag can, for example, be 45 m in length and e.g. 10 m in circumference measured as stretched mesh at the leading end.
• the mesh in most of the bag with be stretched out, so that most of the bag's surface consists of tightly-closed net meshes, where the distance from knot to knot transversely to the trawl direc ⁇ tion is 10% or less of the mesh width.
• the closing of the mesh is held in balance by a force along the circumference of the bag, and which stems from the current of water which is pressed from the interior of the bag out through the net.
• One embodiment of the net is peculiar in that the dimension of the sorting net or nets is considerably greater in the trawl direction than in the transverse direction.
• a preferred embodiment is peculiar in that it has at least one sorting net which has the shape of an elongated rect- angle, and which extends mainly in the bag's longitudinal direction.
• sorting net has a curved shape around its longitudinal axis and appears as a rib on the outside of the catch-bag in the longitudinal di ⁇ rection.
• the breadth of the sorting net measured in the number of openings formed by its mesh along the circumference of the catch-bag is 5-35% of the total number of mesh openings.
• the sorting net be divided in ⁇ to several narrow nets in order to disturb the water cur- rent as little as possible. For example, in a shrimping net, one could insert 6 narrow, longitudinal sorting nets.
• the particularly preferred sorting net is divided into two, each of which is 7-15% of the total number of mesh ope- nings, and which extend substantially throught the whole length of the catch-bag. If the breadth of the sorting net is made considerably larger that the above-mentioned 35%, it has been found that the shape of the trawl is disturbed.
• a further development of this embodiment is peculiar in that the main net is reinforced in the area in front of the foremost part of the sorting net in order to lead the to ⁇ wing forces around the sorting net.
• the forces in the foremost part of the sorting net can be controlled in such a way that the sorting net can also be held distended in the foremost part, otherwise it will tend to fold together in the fore ⁇ most part until all of the pulling forces around the front of the foremost part have been distributed out in the main net.
• meshes with 95 mm stretched, inside mesh openings it is possible, for example, to achieve that the sorting net is fully open if it is ribbed on the extended bag at a distan ⁇ ce of approx. 70 mm.
• a preferred embodiment is thus peculiar in that the edge of the sorting net is ribbed securely to the main net or parts thereof in a known manner.
• the sorting net is ribbed or in another manner secured to a frame of extended net with a mesh size which determines what size opening the mesh of the window is to have. This is in turn determined by the kind of fish it is desired to catch and which legal re ⁇ quirements are valid.
• the window can be 6 mm plaited polyester yarn with an internal stretched mesh size of 95 mm.
• the window is meshed together with 2-4 mm plaited nylon with 74 mm mesh, 6 meshes wide on the longitudinal sides.
• a characteristic feature of the invention is that it per ⁇ mits the sorting window to be produced and controlled at the factory in the form of sorting nets connected in an in ⁇ tegrated manner with at least one longitudinal "frame", which ensures that the sorting net can be inserted in the catch-bag without the mesh of the sorting net changing shape.
• sorting nets are an important precondition for being able to base a fishery regulation on the appli ⁇ cation of sorting nets.
• the essential factor here will be to ensure that the sorting net cannot be mounted so that its mesh is stretched and herewith closed more than that which corresponds to the aproved found minimum size for the species of fish caught. As described above, this can be done by providing the sorting window with a frame of line or net which limits the extent to which the window can be stretched in the longitudinal direction. With yet a further embodiment, the stretching is limited by an edge of shorter half-mesh.
• Another embodiment is peculiar in that in the edge of the sorting net there is a built-in seal, e.g. in the form of a sealing wire which extends along the edge and through the knots, and which can thereby ensure that the sorting net is original.
• a hither- to-unknown form of fishery control which according to the present invention could be far more effective than that which exists.
• the sorting net maintains its guaranteed dimensions and possibly ap ⁇ proved lifetime by using lines or yarns which are coloured in such a way that it can be seen whether or not the origi ⁇ nal rib distance has been maintained or whether the net's lifetime has expired. For example, this can be achieved when the moving of a knot will expose a piece of yarn of another - possibly undyed - colour, or when a coating layer will have worn off at the expiry of the net lifetime.
• the present invention offers the important advantage that the opening in the sorting net can be adjusted in accordan- ce with what is to be fished. This can not be done if, for example, an attempt is made to use the so-called square- mesh net, but it is readily possible with the present sor ⁇ ting net where the bag's longitudinal direction runs dia ⁇ gonally through the mesh of the sorting net.
• the meshes of the sorting net When fishing for herring, the meshes of the sorting net will be mounted on the frame at a slightly shorter distance, so that the diagonal in the transverse direction of the mesh is the greater, corresponding to the cross-section of the herring which has greater height than width.
• the mesh openings are made square, corresponding to the cod's more round shape, and for flatfish the meshes of the sorting net will be mounted on the frame at a slightly greater distance, so that the openings in use become broader in the horizontal direction, corresponding to the flat cross-section of the fish.
• a sorting net with asymmetrical mesh e.g. by making the window from net knotted with a shorter over-yarn (from the shuttle) and longer under-yarn ( from the frame) .
• the mesh openings hereby becomes almost guttiform.
• Such a net is mounted in the catch-bag turned 90° in relation to the bag's longitudinal direction, so that when the bag moves horizontally through the water, the guttiform stands vertically in the sorting window.
• the sorting net's mesh is turned 90° as described above, in that it has been found hereby that the net meshes can better be held open in the desired shape.
• any pull force which extends from the bag's upper panel can be transmitted directly through the diagonally-extending yarn of the sorting window down to the lowermost panel.
• This is an ad ⁇ vantage compared with the case where a square-meshed window has been mounted, where the connection between the upper and the lower panels extends through yarn which stands at 90° in relation to the panels.
• the sorting net or nets can be stiffer than the main net, e.g. with regard to ben ⁇ ding.
• the sorting net or nets can be pre-stressed during the trawl.
• the sorting net or nets can in the main be tension-free, in that they are inserted in such a manner that in the main they do not transfer towing forces during the trawl.
• What is involved here are three different further develop ⁇ ments, each of which can contribute towards maintaining the shape of the sorting net.
• the net is made stiff by reinforcement, either of the yarn itself or by giving it a stiffer coating.
• All three arrangements can contribute to the maintaining of the shape of the sorting net, and also to preventing the flapping of the net in the current.
• Yet another embodiment is peculiar in that a known trawl with a cross-section like a reclining ellipse is equipped with an extended, rectangular sorting net at the sides, i.e. where the curvature of the ellipse is greatest.
• catch-bag consists of an upper part and a lower part, and which in use has the shape of a reclining ellipse wherein two joints extend in the towing direction at the point where the curve of the ellipse is greatest, is peculiar by having a sorting net in the underpart immediately below and along each of the joints. It has been found that with such a net one can practically avoid undesired catch. To this can be added that this embo ⁇ diment is particularly suitable for building into existing nets, because experience has shown that it does not in any way disturb the conditions of flow. It is not necessary to undertake renewed adjustments of the trawl after the sor ⁇ ting nets are mounted.
• a sorting net according to the invention can be specially impregnated, e.g. with acryl latex or rubber latex. It has been found that such an impregnation is particularly de ⁇ cisive in achieving a good result. Firstly, the impregna ⁇ tion contributes towards the damping of the movement of the net itself, but also the damping of the movement of the in- dividual meshes, and this is of great significance because otherwise the fish can be frightened away. Secondly, the impregnation contributes towards increased stiffness of the net mesh, and in this way a greater stability of shape is achieved - the net can better remember its shape. Thirdly, the fish slip easier through the net, and damages to the fish are hereby avoided to a higher degree.
• the net can for example be made of normally twisted or plaited yarn of nylon or poly- ester, which is subsequently impregnated with an agent which ensures firmness of the knots and increases the net's stiffness and elasticity.
• a preferred agent can be a curable latex, e.g. an acrylic latex which is hardened with a melamine formalin resin.
• the agent can also be a curable vinyl-pyridine resin which is hardened with a formaldehyde recorsinol resin.
• the agent can also be a two-component po- lyurethane rubber.
• Particularly preferable agents are weather-resistant rub ⁇ bers such as nitril rubber, which are bound to the net ma- terial by means of a vinyl pyridine latex.
• Impregnation can be carried out in several steps by apply ⁇ ing several layers.
• the hardening is carried out by heating to above 100°C for 1/2 to 5 hours while the net is stretched to the mesh shape which is required in the sorting part.
• the net is suspended in a mesh shape which is stretched to a greater cross measurement than that which is desired during use.
• the greater stiffness and elasticity is achieved by producing the sorting net of a material which in itself possesses these characteristics.
• the net can be made of monofilaments or of yarn with a core of a stiff material. It is important with these embo ⁇ diments that the stiffness of the sorting net can be chosen so that the catch-bag as a whole retains sufficient benda- bility to enable it to be handled in the normal manner du ⁇ ring handling on the boat.
• the sorting net according to the invention can have a mesh orientation so that one of the mesh diagonals extends substantially parallel with the longitudinal direc ⁇ tion of the catch-bag.
• the invention also relates to a method for the manufacture of a net according to the invention, and this method is pe ⁇ culiar in that:
• the panels of the catch-bag are stretched out as during the trawl, and the sorting window is secured in the opening so that it stands as determined under 1 ) and 2) when taken into use,
• the distribution of the pulling forces and the transverse forces (it should be noted that here the pulling forces are to be understood as the towing forces from the fishing vessel) , it is realized that the least detriment to the force distribution is in- curred by forming an elongated opening in the direction of the tow. It is further realized that such an opening can be made substantially tension-free, which in turn provides freedom for the building-in of a sorting net with the de ⁇ sired distension. Trials have shown that it is expedient for fish of a certain size to be desirable even to make the breadth of the sorting net considerably greater than the corresponding opening in the catch-bag during use, so that the sorting net's two long sides curve in towards each other and the sorting net sit like a bulge on the catch- bag.
• fig. 1 shows a trawl rigged as during the tow
• fig. 2 shows a catch-bag of known construction while being towed
• fig. 3 shows a bag with sorting window according to the
• fig. 4 shows different shapes of mesh in the sorting net
• fig. 5 shows a sorting window with a frame of finer mesh.
• the trawl 1 in fig. 1 comprises three main parts; the arms 2, the body 3 and the catch-bag 4.
• the arms are often made of net of a large mesh size, and they serve primarily to frighten and lead the fish towards the middle of the main net.
• the fish are led through the body of the trawl rearwards towards the catch-bag 4, which is that part which collects the catch and in the main determines what will be retained and what will be given the possibility of escape.
• FIG. 2 In fig. 2 is seen the situation in which a catch-bag of known construction is towed over the bottom, and the catch is mixed.
• 11 is the upper panel of the bag
• 12 is its lower panel
• 13 is the connection where the catch-bag is secured to the body 14 of the trawl.
• the meshes will be more or less closed, especially in the middle of the bag, due to the longitudinal towing force.
• the mesh is larger so that smaller fish are pressed out, but are dead or dying due to mechanical damages or ex ⁇ haustion.
• Fig. 3 shows the lower or rearmost end of a trawl with a catch-bag according to an embodiment of the invention.
• the bag 31 is connected to the existing main part 32, of which only a small part is shown, but this part is of conventio- nal construction.
• the bag 31 ends in the so- called lift 33, which comprises the rearmost two meters of the bag 31.
• a limiting strap 34 Around the rearmost end of the bag 31 there is mounted a limiting strap 34 at a distance of 47 cm from the bottom of the bag.
• a sorting net 35 is arranged at each side of the bag 31. The length of this sorting net 35 is
• the bag 31 consists of a plaited polyester 4-6 mm mesh 105 with an internal stretch dimension of 95 mm.
• the opening in the bag 31 is 100 meshes and at the lift 33 it is similarly 100 meshes.
• the sorting net 35 is 77 cm broad at 100% open mesh, and is ribbed on a 12 mm Danline with rib distance 70 mm corresponding to 100% open mesh.
• the sorting net 35 is plaited nylon which is impregnated four times with a hard- able acryl latex, and which is fixed dimensionally and in shape by heat treatment at 125 C C.
• the lift strap 38 lies in plastic rings 2.33 m from the bottom.
• the wear-coat is double-4-plaited polyester with an internal mesh of 210 mm.
• Fig. 4 shows different mesh shapes in the sorting net. They are all shown with vertical orienation as they will stand in the sorting window during use, and the tow direction is shown with arrows.
• 41 is a mesh which is mounted so that the two diagonals 42 and 43 are equal in length. This gives a quadratic opening corresponding to that suitable, for example, for the sorting of cod.
• 44 is a net which, when being mounted in frames or possibly directly in the trawl, has had the vertical diagonal 43 made longer than the horizontal 42, corresponding to a sorting net for e.g. herring.
• 45 shows a section of a sorting window which is made of a net in which every other thread is shortened down, so that the mesh is unsymmetrical. Moreover, this net is turned 90° in relation to the normal, so that the net's depth lies transversly to the bag's longitudinal direction.
• the trawl shown in fig. 3 has been compared with two other trawls of more or less the same size, but without the sor ⁇ ting net according to the invention.
• One of these trawls had a bag of approved 105 mm internally stretched mesh, while the other was a 36 mm herring bag.
• both nets provided a catch of approx. 3,000 fish in 15 2-hour tows. In both cases, the undesired catch was around 70%, and the remainder were cod of the permissible size above 34 cm.

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• Life Sciences & Earth Sciences (AREA)
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• Animal Husbandry (AREA)
• Biodiversity & Conservation Biology (AREA)

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Cited By (3)

Citations (3)

• 1993
  • 1993-09-03 DK DK100193A patent/DK170355B1/da not_active IP Right Cessation
• 1994
  • 1994-09-01 WO PCT/DK1994/000328 patent/WO1995006405A1/en active Application Filing
  • 1994-09-01 AU AU76087/94A patent/AU7608794A/en not_active Abandoned

Patent Citations (3)

Non-Patent Citations (1)

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