WO1998036638A1

WO1998036638A1 - Size-sorting trawl and method of using same

Info

Publication number: WO1998036638A1
Application number: PCT/DK1997/000082
Authority: WO
Inventors: Pade Thomsen
Original assignee: Pade Thomsen
Priority date: 1997-02-21
Filing date: 1997-02-21
Publication date: 1998-08-27
Also published as: AU2021597A

Abstract

In a size-sorting trawl, of which only a part (1) between the entrance part (not shown) and the collecting bag (not shown) is shown, a grille (6) allows free passage towards the collecting bag of small fishes (3), whereas medium-sized fishes (4) and large fishes (5) are urged to pass below the grille (6). In an embodiment (not shown), there is an unobstructed escape opening at the lower edge of the grille (6), allowing both large (5) and medium-sized (4) fishes to escape, whilst in the embodiment shown, only the medium-sized fishes (4) are allowed to escape, as the large fishes (5) are unable to penetrate a sorting net (13) below the grille (6), guiding them into the space (8) behind the grille (6). In both cases, substantially all the small fishes are caught in the collecting bag (not shown).

Description

SIZE-SORTING TRAWL AND METHOD OF USING SAME

TECHNICAL FIELD

The present invention relates to a size-sorting trawl of the kind comprising a) a generally bag-shaped trawl net adapted to be hauled through the water with its entrance opening for- wardmost, b) a first sorting member secured in said net behind said entrance opening and comprising a number of openings the size of which corresponds to the maximum size of fishes of a first, relatively smaller type to be sorted from fishes of a second, relatively larger type, and c) a first, at least one passage adjacent said sorting member and having a size sufficient to allow fishes of said second, relatively larger type to pass there- through.

BACKGROUND ART

The international application PCT/NO92/00071 (SELFI AS) describes a size-sorting trawl exhibiting the features set forth above. In this previously known trawl, the rear side of the first sorting member, constituted by a grille, is open to the surrounding sea, while the passage at the lower end of the sorting member, that extends from the top of the trawl net and at an angle rearwardly and downwardly between the sides of the net, leads to the rearward part of the trawl including the collection bag. With this known arrangement, small fishes will be able to escape through the grille, while larger fishes will pass through the passage to the rearward part of the trawl, finally ending up in the collecting bag.

DISCLOSURE OF THE INVENTION

It is the object of the present invention to modify the principles of the prior-art trawl referred to above in such a manner, that it is possible to catch the small fishes while letting the larger fishes escape, and this object is achieved with a size-sorting trawl of the kind referred to above, characterized in d) that said first sorting member extends across a substantial part of the cross-section of said net, and e) that said first, at least one passage is formed immediately adjacent said first sorting member and adapted to allow fishes of said second, relatively larger type to pass.

With this arrangement, the small fishes will pass through the first sorting member, which may be a grille, into the rearward part of the trawl, ending up in the collec- ting bag, while the larger fishes will pass below the sorting member and through the passage in the net formed below it. Depending on further arrangements set forth in the claims and described in the detailed part of the present description, the relatively larger fishes may be allowed to escape into the surrounding sea or divided into two categories, of which fishes of the larger category are constrained to move into the rearward part of the trawl so as to end up in the collection bag, while fishes of the smaller category constituting medium-sized fishes are allowed to escape into the surrounding sea.

The present invention also relates to a method of fishing, using a size-sorting trawl exhibiting features according to the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following detailed part of the present description, the invention will be explained in more detail with reference to the exemplary embodiments of a size-sorting trawl according to the invention shown in the drawings, in which Figure 1 shows a first embodiment of an intermediate part of a trawl, illustrating its operation, Figure 2 shows a grille used in the intermediate part shown in Figure 1 as viewed along the arrow II in Figure

1, Figure 3 shows a second embodiment comprising second sorting means,

Figure 4 shows a third embodiment, that may be integrated with either of the previously mentioned embodiments, comprising means for influencing the behaviour of some of the fishes encontered, and

Figures 5 and 6 show a fourth embodiment, in which both sorting members are grilles.

It should be noted that the drawings in a purely diagram- matic manner show solely those parts of a particular exemplary embodiment of a trawl necessary for the understanding of the invention, and that persons skilled in this field will know how to apply the principles of the invention to a trawl used in practical operation. DESCRIPTION OF THE PREFERRED EMBODIMENTS

Figure 1 shows an intermediate part 1 of a fishing trawl adapted to be hauled through the sea in the direction shown by an arrow 2, i.e. toward the left in the drawing. The intermediate part 1 is in the normal manner placed between an entrance part (not shown) and a collecting bag (likewise not shown) .

The fishes having been intercepted by the entrance part can be divided into three categories, viz.

- small fishes 3,

- medium-sized fishes 4, and

- large fishes 5.

The space within the intermediate part 1 is divided by a grille 6 into a forward space 7 and a rearward space 8, said grille 6 in this embodiment sloping steeply rearward- ly and downwardly from the top to the bottom of the inter- mediate part 1.

In the bottom of the intermediate part 1 and immediately in front of the lower part of the grille 6, an escape passage 9 communicates the forward space 7 with the sur- rounding sea.

As shown in Figure 2, the grille 6 consists of a frame

10 carrying a number of rods 11, the spacing 12 of the grille 6 being such, that the small fishes 3 can pass freely through the grille 6, whilst the medium-sized fishes 4 and the large fishes 5 cannot get through, and will - presumably in part by instinct, in part for purely mechanical reasons - proceed downwardly along the rods

11 of the grille 6 and escape into the sea through the escape passage 9.

In this manner, the catch (not shown) collected in the collecting bag will consist substantially exclusively of small fishes 3, that may be or may not belong to the category "industrial fish", normally caught for industrial purposes, such as making fish meal and fish oil.

It may be considered desirable to catch also some of the large fishes 5, while it is less desirable to catch the medium-sized fishes 4, as it is preferable to allow the latter to escape and grow to full size, so as to belong to the category of large fishes 5 (possibly to be caught next year) .

Figure 3 shows an embodiment, with which it is possible to catch both the small fishes 3 and the large fishes 5, at the same time allowing the medium-sized fishes 4 to escape into the sea. This is achieved by means of a second sorting member in the form of a relatively coarse sorting net 13 with a mesh size allowing the medium-sized fishes 4 to escape, while the large fishes 5 are guided through an opening 14 in the bottom of the intermediate part 1 below the rearward space 8 into the latter, so as to finally end up in the collecting bag (not shown) .

This means, of course, that the catch collected in the collecting bag will now most probably consist of a relatively great number of small fishes 3 and a relatively small number of large fishes 5. Because of the great difference in size, however, the final sorting of these two categories should present no difficulties.

The embodiment shown in Figure 4 is based upon that shown in Figure 1, but differs from the latter in comprising an urging net 15 of extremely fine mesh extending from a point well in front of the grille 6 on the bottom of the intermediate part 1 lying below the forward space 7 and at an angle upwardly and rearwardly towards the grille 6. In operation, the urging net 15 will urge small fishes 3 in the upward direction, thus reducing the number of small fishes 3 that would otherwise escape through the escape passage 9. The medium-sized fishes 4 and the large fishes 5 will also be urged upwards, but the grille 6 will force them to swim downwards past the rearward end of the urging net 15 and through the escape passage 9.

The spacing 12 between the rods 11 in the grille, as well as the mesh size of the sorting net 13 will, obviously, be adjusted so as to suit the various sizes of the fishes expected to be encountered when using the trawl comprising the intermediate part 1. As an example it may be mentioned that during said practical trials, a spacing 12 in the grille 6 of 25 mm proved suitable, likewise a mesh size of 200 mm for the sorting net 13. To maintain the sorting net 13 in a configuration, in which it will have the desired effect, it can advantageously be attached to a framework (not shown) consisting e.g. of one or more pieces of relatively stiff rubber hose, such as used in hydraulic equipment.

In Figure 3 , the passage 14 is shown as lying immediately behind the grille 6. It does, however, lie within the scope of the invention to place the passage 14 at some distance from the grille 6. If so, the sorting net 13 or an equivalent grille would have to be lengthened correspondingly . The material for the intermediate part 1 as well as for the sorting net 13 and the urging net 15 may be the same as is normally used in marine environments, such as polyethylene, nylon, polyester or the like. The grille 6 is preferably made from a suitable metal, such as stainless steel, with a smooth surface finish to avoid damage to the various fishes coming into contact with it.

As indicated above, it is also possible within the scope of the present invention to use a grille instead of the sorting net 13. Figures 5 and 6 show such a grille 13 * , the front end of which is attached, such as by a hinged connection, to the lowermost end of the frame of the grille 6¹, the latter ending downwardly some distance short of the lowermost end of the frame so as to leave an escape passage 9 ' allowing fishes to pass unhindered from a forward enclosure 16 below the urging net 15 to a rearward enclosure 17 formed by the grille 13 ' and a part 1 ' of the trawl net 1 having been cut free at the lower end of the frame of the grille 6', to which the bottom of the forward part of the net 1 is secured, the forward end of the part l¹ being secured to the lowermost end of the grille 6¹ itself, i.e. at the top of the passage 9 ' . The rearward end of the part 1 ' is held in a manner not shown at some distance above the rear end of the grille 13 ' , thus forming a passage 14 ' , the edge having been created by cutting the part 1 ' free from the net 1 in this location being secured to the rearward end of the grille 13 ' .

With the embodiment of Figures 5 and 6 in operation, the medium-sized fishes 4 and the large fishes 5 will pass downwardly past the front edge of the urging net 15 into the forward enclosure 16, from which they pass unhindered through the passage 9 ' into the rearward enclosure 17 , from which the medium-sized fishes escape into the sea through the grille 13'. The spacing of the latter is, however, too small to allow the large fishes 5 to escape, so that they will pass through the passage 14 ' into the rearward space 8 and be caught in the collecting bag as decribed above with reference to Figure 3.

Dimensions of equipment used in practical trials (Vide Figures 3 and 4) :

Net 1:

Width: 1300 mm Height: 1500 mm Mesh size: 50 mm Material: PET

Grille 6:

Width: 1300 mm

Height: 2000 mm

Slot width: 25 mm

Material: Stainless steel

Angle with long, direction of trawl: 65°

Passage 9:

Length (in direction of movement) : 0-300 mm

Width: 1300 mm

Passage 14 :

Length (in direction of movement) : 0-30 mm

Width: 1000 mm Net 13:

Width: 2100 mm (as cut from stock) Depth: 500 mm (measured from trawl bottom)

Length: 4000 mm Mesh size: 200 mm Material: PET Reinforcement : 038x2000 mm hydraulic rubber hose

Net 15:

Width: 1300 mm

Height (rear edge) 1000 mm (measured from trawl bottom along grille 6)

Oblique length: 2000 mm Mesh size: 22 mm Material: Nylon

In the above part of the description referring to the embodiments shown in the drawing, the various parts are described as having certain orientations and/or shapes. It should be noted, however, that many changes and modifications are possible within the scope of the invention as defined by the claims.

Thus, the grille 6 can be placed at right angles to the trawl net 1 instead of obliquely as shown. Further, the passages 9 and 14 may be situated in the sides or the top of the trawl net 1. LIST OF PARTS

1 intermediate part

2 arrow 3 small fishes

4 medium-sized fishes

5 large fishes 6,6* grille

7 forward space 8 rearward space

9,9' escape passage

10 frame

11 rods

12 spacing 13 sorting net

13 ' sorting grille

14 opening 14 ' passage

15 urging net 16 forward enclosure

17 rearward enclosure

Claims

1. Size-sorting trawl of the kind comprising a) a generally bag-shaped trawl net (1) adapted to be hauled through the water with its entrance opening forwardmost, b) a first sorting member (6,6') secured in said net behind said entrance opening and comprising a number of openings (12) the size of which corresponds to the maximum size of fishes of a first, relatively smaller type (3) to be sorted from fishes of a second, relatively larger type (4,5), and c) a first, at least one passage (9,9") adjacent said sorting member (6) and having a size sufficient to allow fishes of said second, relatively larger type (4,5) to pass therethrough, characterized in d) that said first sorting member (6,6') extends across a substantial part of the cross-section of said net (1) , and e) that said first, at least one passage (9,9') is formed immediately adjacent said first sorting member (6,6') and adapted to allow fishes of said second, relatively larger type (4,5) to pass.

2. Trawl according to claim 1, characterized in that said at least one passage (9) is an opening in said net (1) in front of said first sorting member (6) .

3. Trawl according to claim 1, characterized by a second sorting member (13, 13') having openings, the size of which corresponds to a maximum size of some of the fishes of said, relatively larger second type (4,5); said second sorting member (13, 13') be placed so as to allow fishes (4) of a size up to said maximum size to pass into the surrounding sea, and to constrain the fishes (5) of a size above said maximum to move within said trawl net (1) behind said first sorting member (6, 6').

4. Trawl according to any one or any of the claims 1-

3, characterized by an urging net (15) of substantially finer mesh than said trawl net (1) extending from a point at a distance in front of and in the same side of said trawl net (1) as said first, at least one passage (9, 9') to a point close to said first sorting member (6, 6') and at a distance from said first, at least one passage (9, 9' ) .

5. Trawl according to any one or any of the claims 1-

4, characterized in that said first sorting member (6, 6') is a grille constituting a number of parallel rods (11) spaced from each other and from the parallel sides of the frame of said grille so as to form said openings (12) .

6. Trawl according to any one or any of the claims 3-

5, characterized in that said second sorting member (13) is a piece of net.

7. Trawl according to any one or any of the claims 3- 5, characterized in that said second sorting member is a grille (13'), the rods of which extend substantially parallel to the direction of movement of the trawl.

8. Trawl according to claim 7, characterized in a) that said first sorting member (6') is placed in a frame partly covered by it so as in the remaining part of the frame to form said first, at least one passage (9 ' ) , b) that the edge of said frame on the side of said passage (9') facing away from said first sorting member (6') is secured to the forward edge of said grille (13 ΓÇó) as well as to a forward free edge in said net (1) formed by cutting a first transverse slit in the net, c) that the rearward edge formed by cutting said first transverse slit is secured to the edge of said first sorting member (6') adjacent said passage, and d) that the rearward edge of said grille (13 ΓÇó ) is secured to a rearward free edge in said net (1) formed by cutting a second transverse slit in the net (1) , the corresponding forward free edge being placed at a distance from said rearward free edge so as to form a passage (14') leading into a rearward space (8) .

9. Trawl according to any one or any of the claims 1- 8, characterized in that said first sorting member (6, 6') extends at an angle with the longitudinal direction of said trawl net (1) , having its rearwardmost end or side adjacent said first, at least one passage (9, 9').

10. Trawl according to any one or any of the claims 1- 9, characterized in that in operation, said first, at least one passage (9, 9') is in the bottom part of said trawl net (1) .

11. Method of fishing using a size-sorting trawl of the kind set forth in the preamble of claim 1, characterized by the use of a size-sorting trawl exhibiting the features set forth in the characterizing clause of claim 1, possibly also one or more of the features set forth in claims 2-10.