SE542154C2

SE542154C2 - Shrimp trawl for selection of catch

Info

Publication number: SE542154C2
Application number: SE1850161A
Authority: SE
Inventors: Dag Amtsen
Original assignee: Ecco Reker Havfruen As
Priority date: 2015-07-17
Filing date: 2016-07-08
Publication date: 2020-03-03
Also published as: WO2017014641A1; IS9089A; DK179971B1; NO339612B1; DK201870090A1; NO20150932A1; SE1850161A1

Abstract

The present invention relates to a shrimp trawl for selection of catch, wherein the shrimp trawl comprises: a conical shaped net having an open end facing the tow direction of the shrimp trawl and a cod end for catch in a second narrower end;a grid (6) with a preferably rectangular shape corresponding to the inside of the shrimp trawl when it is slanted and which comprises longitudinally extending spokes, wherein the spokes are spaced apart and in which the grid is inclined rearward from its lower part to its upper part; a hole (5) in the shrimp trawl over the grid; a first guide net (1) which is positioned some distance in front of the grid and is sewn into or attached to the trawl and inclined downward and rearward from the upper portion of the shrimp trawl at the lower part of the grid (6); and is characterized by comprising the first guide net being tightened at its lower end with a resilient band (2) attached to the side wall of the trawl at the bottom, 0 to 20 cm in front of the grid and 10 to 30 cm above the bottom and the lower part of the grid; a first bottom net (4), having a larger mesh width than the trawl, inserted into an area in front of the grid (6), where the mesh has a direction substantially parallel to the longitudinal axis, a second guide net (7) positioned at the upper and rear end of the grid and inclined downward and backward toward the lower part of the shrimp trawl toward the cod end (9); and a second bottom net (8), having a larger mesh width than the trawl, mounted in an area from the bottom of the grid until the end of the guide net (7), wherein the mesh has a direction substantially parallel to the longitudinal axis of the trawl.

Description

SHRIMP TRAWL FOR SELECTION OF CATCH BACKGROUND A major problem within trawling for shrimp has for many years been bycatch of fish and small shrimps, which are not marketable. It is therefore alleged, correctly, that bycatch largely is dumped in the sea by fishermen. It is forbidden to release bycatch / shrimp spawn from Norwegian fishing boats. This should be brought for delivery on shore. As bycatch and shrimp spawn, etc. have no application. The bulk of this is destroyed.

The Fishing Department and researchers have pointed out this for long and many attempts have been made to do a selection of the catch during the trawling process, i.e. by trying out several modifications prawn trawls such as insertion of a grid that filters out unwanted organisms such as small shrimps / shrimp spawn an thus avoids ending up in the cod end. The cod end is the terminus of a trawl whereby catch finally is pulled up in the boat and further processed there.

After extensive destruction of bycatch small fish and shrimps / shrimp spawn are prevented from growing up to a form sustainable population. Directorates and regulatory authorities therefore set very low quotas for fishing to prevent this. This means again that fishing becomes less or very little profitable. It is in everyone's interest to find trawl methods / solutions that provide a sustainable and predictable fishery.

Researchers in Norway have been working for 20-30 years on various measures for selecting organisms that enter a trawl (as mentioned grid), but until today there is nothing that works satisfactorily.

Insertion of grids in trawls is mandatory for Norwegian trawlers doing shrimp fishing south of 62 degrees latitude. In Fig. 1 it is illustrated a standard selection grid used today.

Fig. 2 shows the principle for catch with sorting grid mounted in a shrimp trawl. The catch is led into the trawl towards the bottom thereof by means of a mounted guide net. Thereafter the catch is guided up along the grid where shrimp and small fish pass through and into the cod end. Fish larger than 19mm thickness passes over the grid and out through an opening in the upper part of the trawl and out into the open sea again. This system selects only fish and other organisms that have a thickness greater than 19 mm (19 mm is the requirement of maximum opening in the selection grid). Today it works in a way that everything that comes through the selection grid ends up in the cod end. When this is hoisted up into the boat, the catch is in principle injured or dead, according to the research community. This implies that bycatch cannot be released into the sea again in a living state, but must be taken to land for inspection / use, but mostly ends up being destroyed.

It is possible to solve the problem to some extent by using larger mesh widths in the cod end or modifications in connection with this. Fishermen are obviously not very interested in this because this method also selects some of the shrimps that could have been put on the market, in other words, this solution is not effective in practice.

The researchers have for many years worked with an evolution of the standard grid (Fig. 3). This modification has been tried many times before, but has so many restrictions that it is considered unsatisfactory and is in principle of little use; As mentioned, the basis of the standard grid where the lower part has inserted a smaller grid with narrower gaps of approx. 9 mm (Figure 3 and 4). The idea is that the shrimp spawn "runs through" and slips past into the lower part of the trawl, and go out from there through a bottom net with large mesh width, which are inserted into the trawl along with a guiding net with a fine mesh, which runs from the division between the standard grid and the smaller grid directly back to sea again.

This system can work under ideal conditions as when it is a low volume of small shrimps or fish spawns. But nature can show itself from many sides and in practical fishing conditions are rarely ideal. What happens in real life is that this kind of grid clogs up after a while (packed with small shrimps, etc.) and then has no practical function any more. Several boats have tried it, with the conclusion that it functions poorly and is very inconvenient to handle at sea.

The present invention seeks to solve these problems by providing a shrimp trawl for selection of capture, where the shrimp trawl includes a conically shaped net having an open end facing the tow direction of the shrimp trawl and a cod end for capture in a second narrower end. The shrimp trawl further comprises a grid with a preferably rectangular shape corresponding to the inside of the shrimp trawl when it is slanted and which comprises longitudinally extending spokes, wherein the spokes are spaced apart and the grid is inclined rearward from the lower portion of the trawl to the upper portion so that the catch is guided over the grid by the flow of water that occurs when the trawl is pulled forward. The shrimp trawl also includes a hole in the shrimp trawl above the grid, so that the part of the catch which does not pass through the grid exits the trawl through the hole. The shrimp trawl further comprises a first guiding net which is positioned a short distance forward from the grid and inclined downward and rearward from the upper portion of the shrimp trawl towards the lower portion of the grid and thus guides the catch against the lower part of the grid.

The novelty of the invention is that the first guide net is tightened at its lower end with a rubber band attached to the trawl wall at the bottom of trawl, 0 to 20 cm in front of the grid and 10 to 30 cm above the bottom and the lower part of the bottom of the grid; that a first bottom net with a larger mesh width than the trawl is positioned in an area in front of the grid, where the mesh has a direction substantially parallel to the longitudinal axis of the trawl, so that the mesh maintains its square shape when the trawl is in use; that a second guide net positioned at the upper and rear end of the grid and inclined downward and backward against lower portion of the shrimp trawl toward the cod end; and that a second bottom net with a larger mesh width than the shrimp trawl is inserted into an area between the grid and where the second guide net reaches the bottom of the trawl, wherein the mesh has a direction substantially parallel to the longitudinal axis of the trawl, so that the mesh retains its square shape when the trawl is in use; An important element of this invention is that the different behavior of the various organisms is an important part of the reason why the setup works. It seems that adult shrimps increasingly push their way through obstacles, while other organisms and prawn spawns shy away from obstacles. Thus, it will only work with shrimp or organisms with similar behavior.

Brief Description of the Figures The present invention will now be described by way of example, with reference to the accompanying drawings, in which: Figure 1 shows a prior art grid.

Figure 2 shows prior art with guide net and grid as it is used in the industry.

Figure 3 shows a divided grid with a lower part having a smaller distance between the spokes to filter unwanted small shrimps and organisms.

Figure 4 shows a trawl setup with divided grid.

Figure 5 shows a trawl setup according to the invention.

Figure 6 shows how the lower part of the guiding nets 1 and 2 are held by a biased elastic to the side wall of the trawl.

Figure 7 shows a three-dimensional drawing of the present invention wherein the location of the bottom nets is evident.

Detailed description In the following the direction towards the boat that pulls the trawl, is designated as forward and the direction toward the cod end is rearward. Mesh width and direction of masks are only disclosed where they differ from the prior art. That is, the trawl, guide nets and cod end has mesh widths and orientations according to prior art. The same applies to the angles used in the setup guide nets and the grid in the trawl. An important point is that the meshes of the shrimp trawl nets has a direction in which the tension of the trawl when pulled by a boat travels along the diagonal of the mesh, which means that these are diamond-shaped and provides the whole trawl elasticity. To date regulations says that the mesh width in trawl and cod end should be a maximum of 36 mm and the distance between the spokes in the grid will be a maximum of 19 mm. The following describes the catch once through the trawl of the invention. When it comes to scaling, a large trawl primarily has a larger opening, while the rest are mostly the same. That is, the size of the trawl primarily affects how long the trawl is out and not the size of selection mechanism.

The catch comes into the trawl as usual and counters a first guide net 1, as shown in fig. 2, 4, and 5. The lead net 1 slopes down from the upper portion of the trawl rearward toward the lower portion to a grid 6 and is sewn into or attached to the trawl wall. The guide net is at its lower end biased by an elastic band 2 as shown in fig. 6, attached to the trawl walls and runs in an approximately straight line from side to side in the trawl 0-30 cm in front of the grid 6 so that the lower end of the first guide net is horizontal at a distance 10 to 30 cm from the bottom and the lower part of the grid, and not as today where the lower end forms an arc that makes the catch mainly end up in the middle of the grid thus becoming less effective (as shown in fig. 1 and 3). If the catch builds up, the elastic of the first lead net 1 will stretch and release more catch over the grid. The primary task of the guide net 1 is to guide the catch down to the lower portion of the trawl and feed it in over the grid.

In the present inventions as shown in fig. 2, and 5, a first bottom net 4 with square mesh is inserted into the bottom of the trawl, directly in front of the grid. The masks have a direction which is 45 degrees with the meshes of the trawl. Or in other words: the mesh is approximately parallel to the longitudinal axis of the trawl. This means that the mesh of the bottom net is not deformed when the trawl is pulled, while the meshes of the rest of the trawl is deformed from a square shape into a diamond shape. This means in turn that it is much easier for organisms that are caught in the trawl to get out through the bottom net than the rest of the trawl. Experiences from experiments conducted by the applicant have shown that a mesh width of 45 mm in the first bottom net 4 gives optimum results for shrimp fishing in Kattegat and the North Sea at depths of 0 to 400 meters. The area of the first bottom net 4 covers virtually the entire width of the grid multiplied by a length of 0.5 to 10 meters, most preferably between 3 - 6 meters. It can be expected that adjustments to these amounts must be made using the invention in other regions, where it may be a different size distribution of shrimp or another species of shrimp.

The first guide net 1 of the present invention, as shown in fig. 5, has an extension 3 of 10 to 100 cm, more preferably 20 to 30 cm, which is hung over the grid after the elastic band, which is not attached to the sides. This will, because of the water flow in the trawling direction, lie on the lower part of the grid 6 as a minor obstacle. Because of this the catch will to some extent have a longer stay at the lower part of the grid.

Different species of fish and shrimp have different behavior and response patterns and it turns out that most of the small fish / spawns will go through the meshes of the first bottom net 4 and out to the open sea again, while the shrimp do not. The mesh width can be determined by what size you choose to select away, most preferably a mesh width of 38 -55mm. Since shrimp reacts differently to resistance compared to fish and spawns, most of the shrimp go through the grid.

Then the catch is filtered through the grid and bigger fish pass over the grid and through the opening 5 in the upper part of the trawl, which also is common in prior art.

In the present invention a second guide net 7 is mounted at the top of the grid and slopes downward and rearward toward the bottom of the trawl. The second guiding net 7 is to be mounted at an angle to the longitudinal axis of the trawl of between 20 and 50 degrees, preferably about 35 degrees or the same angle as the angle between the first guide net 1 and the longitudinal axis of the trawl. The second guide net 7 ends where the second bottom net 8 ends. Alternatively, as will be explained later a third guide net 14 may be attached to the end of the second guide net 7, in which case the second bottom net 8 ends at the end of the third guide net 14. The second guide net is from 5 -15 meters and the lower comers of the second guide net are attached to, or near, the two rear comers of the bottom net 8. Most of the shrimp and the remainder of spawns and small fish which have passed through the grid 6 will thus be directed down towards the bottom of the trawl where spawns and small fish swims through the second base net 8 and the shrimp swim into the cod end.

In the present invention there is inserted a second bottom net 8 with square meshes which, like the first bottom net 4 is mounted at an angle of 45 degrees with the meshes of the trawl. The second bottom net 8 is mounted in an area from the bottom of the grid until the end of the guide net 7, where it ends near the cod end 9 of the trawl which is 5 to 15 meters from the grid 6, as shown in Figure 5. Based on applicant's experience, it appears that small shrimps / spawn passes through the second bottom net 8 and into the open sea again. Best results were obtained with a mesh width of 45 mm, which is slightly larger than the trawl, but in practice quite much larger because the meshes of the second base net 8 is not deformed by the tension in the trawl. Large shrimps will proceed from the bottom of the second guide net 7 and into the cod end.

In another embodiment shown in figure 7, a third guide net 14 is attached to the rear and bottom end of the second guide net 7 and runs parallel with an extended second bottom net 8 towards, but not into, the cod end 9 of the trawl. In this embodiment the second bottom net is up to 15 meters long. The effect of this net is to further improve the selection of shrimp sizes, and can be particular advantageous in regions with large quantities of small shrimps. It is also conceivable that the second and third guide net both have the same angle with respect to the centerline of the trawl and thus constitutes one guide net with a low angle with respect to the centerline of the trawl.

As described here, we have tested a shrimp trawl that selects away most of unwanted catch and especially spawns from the shrimp that is kept for processing and sales. The present shrimp trawl meet government requests for resource and environmental management at sea and the applicant wishes to emphasize that worldwide a large number of spawn and small fish no longer need to be dumped or destructed. 3. July 2015 the coastguard vessel Aalesund undertook an inspection of the catch which was obtained with the present invention and noted that 100% of the shrimp below 60 mm were selected back into the open ocean again.

Moreover, it appears that the present invention selects away 70-80 % of small fish and spawn that would otherwise have ended up in the cod end.

What is described in the above is only examples and is not intended to limit the invention. Many more variations with regard to scaling and mesh widths and design of the grid is possible, and is only limited by the independent claim.

Claims

1. Shrimp trawl for selection of catch, wherein the shrimp trawl comprises: a conical shaped net having an open end facing the tow direction of the shrimp trawl and a cod end (9) for catch in a second narrower end; a grid (6) with a preferably rectangular shape corresponding to the inside of the shrimp trawl when it is slanted and which comprises longitudinally extending spokes, wherein the spokes are spaced apart and in which the grid is inclined rearward from its lower part to its upper part; a hole (5) in the shrimp trawl over the grid (6); a first guide net (1) which is positioned some distance in front of the grid (6) and is sewn into or attached to the trawl and inclined downward and rearward from the upper portion of the shrimp trawl at the lower part of the grid (6); and is characterized by comprising the first guide net being tightened at its lower end with a resilient band (2) attached to the side wall of the trawl at the bottom, 0 to 20 cm in front of the grid and 10 to 30 cm above the bottom and the lower part of the grid; a first bottom net (4), having a larger mesh width than the trawl, inserted into an area in front of the grid (6), where the mesh has a direction substantially parallel to the longitudinal axis, a second guide net (7) positioned at the upper and rear end of the grid and inclined downward and backward toward the lower part of the shrimp trawl toward the cod end (9); and a second bottom net (8), having a larger mesh width than the trawl, mounted in an area from the bottom of the grid until the end of the guide net (7), wherein the mesh has a direction substantially parallel to the longitudinal axis of the trawl;

2. Shrimp trawl according to claim 1 wherein the first guide net (1) has an extension (3) that hangs over the grid (6) and delays further movement of the catch along the grid (6).

3. The shrimp trawl according to claim 1 wherein the angle between the second guide net (7) and the longitudinal axis of the trawl is between 20 and 50 degrees, preferably 35 degrees.

4. Shrimp trawl according to claim 1 where the angle between the second guide net (7) and the longitudinal axis of the trawl is the same as the angle between the first guiding net (1) and the longitudinal axis of the trawl.

5. Shrimp trawl according to claim 1 wherein the lower comers of the second guide net (7) are secured to the rearmost two comers of the second bottom net (8).

6. Shrimp trawl according to claim 1 wherein The first bottom net (4) substantially extends over the entire width of the grid in an area of the grid (6) and 0.5 to 5 meters forward from the grid (6), more preferably from the grid (6) and 1-2 meters forward from the grid (6), and where the mesh width of the first bottom net (4) is from 20 to 60 mm, preferably about 45 mm; second bottom net (8) substantially extending over the entire width of the grid in an area from the grid where the second guide net (7) is ending near the bottom of the trawl and 2 to 10 meters, more preferably 3 to 6 meters all the way up to the grid (6), and the mesh width of the second bottom net (8) is from 20 to 60 mm, preferably about 45 mm.

7. Shrimp trawl according to any one of the previous claims wherein a third guide net (14) is mounted to the lower end of the second guide net (7) and runs parallel with an extended second bottom net (8) towards, but not into, the cod end (9).