FISH GRADING DEVICE

Abstract: A fish grading device (1) is formed from an array of generally rectangular apertures (2), each of which is formed by two long tubes (3) and two short tubes (4) of plastics material mounted to a loop of fishing net (5). Each loop of fishing net (5) is formed by crimping the ends of the loop by means of a metal crimp (6). Each of the tubes (3, 4) can rotate freely about its longitudinal axis, so that a fish brushing against a tube (3, 4) will cause the tube to rotate, and will therefore avoid becoming snagged on the tube. When such a fish grading device (1) is included in a fishing net and the net is dragged through the water, small fish are able to swim through the rectangular apertures (2), whereas larger fish are not. Thus only fish of a desired minimum size are caught.

Description: FISH GRADING DEVICE The present invention relates to fish grading devices and relates particularly, but not exclusively, to fish grading devices for incorporation into fishing nets. Fish grading devices are known which consist of a fishing net having a mesh size such that fish above a certain size cannot swim through the net and are therefore retained in the net, while smaller fish can escape through the apertures in the net. Known fish grading devices of this type suffer from the disadvantage that fish can be injured by becoming snagged on the net while trying to pass through the apertures. Preferred embodiments of the present invention seek to overcome the above disadvantages of the prior art . According to an aspect of the present invention, there is provided a fish grading device comprising a framework of interconnected substantially rigid elongate members forming a plurality of loops, each said loop defining an aperture not exceeding predetermined dimensions, wherein each said loop is pivotable relative to the or each said loop adjacent thereto. By providing a plurality of loops formed by interconnected substantially rigid members such that each loop is pivotable relative to the or each loop adjacent thereto, this gives the advantage that fish are less likely to become snagged on the substantially rigid elongate members than on threads of a fishing net, but the fish grading device is still sufficiently flexible that it can be wound onto a reel or otherwise made compact for convenient handling or transport. In a preferred embodiment, each said substantially rigid elongate member can rotate about its longitudinal axis. This provides the advantage of minimising the risk that a fish will become snagged on one of the substantially rigid elongate members while trying to pass through one of the apertures of the device. Each said substantially rigid elongate member may be tubular. The substantially rigid elongate members may be interconnected by means of elongate flexible members. In the case of tubular substantially rigid elongate members being interconnected by elongate flexible members, this provides the advantage that the fish grading device is flexible when not under tension, but becomes rigid when under tension such that the apertures remain of substantially constant dimensions . The or each said elongate flexible member may be a string or thread. The or each said elongate flexible member may form a respective loop corresponding to each said loop of said interconnected substantially rigid elongate members. In a preferred embodiment, a plurality of said loops of elongate members are each formed from four said substantially rigid elongate members. Each of said loops of substantially rigid elongate members is preferably substantially rectangular. According to another aspect of the invention, there is provided a fishing net including a fish grading device as defined above. According to a further aspect of the present invention, there is provided a method of grading fish using a fish grading device as defined above. A preferred embodiment of the invention will now be described, by way of example only and not in any limitative sense, with reference to the accompanying drawings, in which :- Figure 1 is a schematic elevation view of part of a fish grading device embodying the present invention; Figure 2A is a perspective view of a first embodiment of fishing net incorporating the fish grading device of Figure 1; Figure 2B is an enlarged view of part of the fishing net of Figure 2A; and Figure 3 is a schematic elevation view of a second embodiment of fishing net incorporating the fish grading device of Figure 1. Referring to Figure 1, a fish grading device 1 is formed from an array of generally rectangular apertures 2, each of which is formed by two long tubes 3 and two short tubes 4 of plastics material mounted to a loop of fishing net 5. Each loop of fishing net 5 is formed by crimping the ends of the loop by means of a metal crimp 6. Each of the tubes 3 , 4 can rotate freely about its longitudinal axis, so that a fish brushing against a tube 3, 4 will cause the tube to rotate, and will therefore avoid becoming snagged on the tube . Tubes 3, 4 defining two adjacent apertures will have two loops of fishing line 5 passing therethrough, for example as shown at locations 7. When the fish grading device 1 is placed under tension, the dimensions of apertures 2 are prevented by tubes 3, 4 from being reduced, but when the device 1 is not under tension, it is relatively flexible, and can therefore be handled easily, for example would onto a reel on a fishing boat . Referring now to Figure 2A, a fishing net 10 for use in the commercial fishing sector is dragged by means of lines 11 by a boat (not shown) such that fish are drawn into mouth 12 of the net 10. The net 10 is provided with a number of panels formed by fish grading devices 1, three such panels being shown in Figure 2A, two of which are in the central location of the net 10, and one of which is at cod end 13 of the net (Figure 2B) . The operation of the net shown in Figures 2A and 2B will now be described. When the net 10 is dragged behind a boat, fish are drawn into the net 10, and only fish that are sufficiently small to pass through apertures 2 (Figure 1) can escape from the net. As a result, larger fish are retained in the net, while smaller fish can escape. As the net 10 is dragged behind the boat, the loops 5 of the fish grading device 1 are placed under tension, as a result of which the tubes 3, 4 are drawn closer together and the rigidity of the tubes prevents the dimensions of the apertures from reducing. At the same time, if a fish is trying to pass through one of the apertures 2 and is caused by other fish to be pressed against one of the tubes 3, 4, the tube 3, 4 can rotate about its longitudinal axis, which reduces the risk of a fish becoming injured by becoming snagged on the threads of the fishing net . Figure 3 shows a sweep net for use in the aquaculture industry in confining fish to a selected volume of water, for example within a sea cage or shore tank system of a fish farm. The sweep net 20 is formed by a net 21 suspended from float 22, and incorporating a fish grading device 1 as shown in Figure 1. It will be appreciated by persons skilled in the art that the above embodiments have been described by way of example only, and not in any limitative sense, and that various alterations and modifications are possible without departure from the scope of the invention as defined by the appended claims.

Claims: C AIMS 1. A fish grading device comprising a framework of interconnected substantially rigid elongate members forming a plurality of loops, each said loop defining an aperture not exceeding predetermined dimensions, wherein each said loop is pivotable relative to the or each said loop adjacent thereto. 2. A device according to claim 1, wherein each said substantially rigid elongate member can rotate about its longitudinal axis. 3. A device according to any one of the preceding claims, wherein each said substantially rigid elongate member is tubular. 4. A device according to any one of the preceding claims, wherein the substantially rigid elongate members are interconnected by means of elongate flexible members. 5. A device according to claim 4, wherein the or each said elongate flexible member is a string or thread. 6. A device according to claim 4 or 5, wherein the or each said elongate flexible member forms a respective loop corresponding to each said loop of said interconnected substantially rigid elongate members. 7. A device according to any one of the preceding claims, wherein a plurality of said loops of elongate members are each formed from four said substantially rigid elongate members. 8. A device according to claim 7, wherein each of said loops of substantially rigid elongate members is substantially rectangular . 9. A fish grading device substantially as hereinbefore described with reference to the accompanying drawings. 10. A fishing net including a fish grading device according to any one of the preceding claims . 11. A method of grading fish using a fish grading device according to any one of claims 1 to 9.

Inventors: JOHNSON IVOR GILBERT, JOHNSON, IVOR, GILBERT
Applicants: JOHNSON IVOR GILBERT, JOHNSON, IVOR, GILBERT
Application year: 2000
Main classification: A01K75
IPC codes: A01K61, A01K73, A01K75