APPARATUS FOR GROWING AND HARVESTING SHELLFISH, PARTICULARLY MUSSELS

Abstract: A mussel cultivation means particularly for use in mussel spat collection. A plurality of flexible linear support means on which mussels can grow are joined at intervals by rigid spacing means, typically plastic overmouldings. The invention also provides a vessel for harvesting mussels and a mussel collection system comprising both a harvesting vessel and mussel cultivation means.

Description: APPARATUS FOR GROWING AND HARVESTING SHELLFISH, PARTICULARLY MUSSELS The present invention relates to a shellfish culture track and a shellfish harvesting vessel for growing and harvesting shellfish, particularly mussels. At the present time, mussels are usually cultured on long lines. Mussels grow on a series of pegged ropes (mussel droppers) which hang underwater from head ropes (headlines) . The headlines are supported by purpose made floats and are typically 100m long. Usually, two headlines will be supported parallel to each other, one on either side of the floats. Mussel droppers are colonised by larval mussels (spat) in the sea at an appropriate time of year. A pegged rope is used instead of a plain rope in order to increase the surface area available for mussels to colonise and to prevent mussels sliding down the rope as the weight of mussels increases. Instead of a pegged rope, lengths of flat plastic sheet are used in some countries - this provides a larger surface area than a simple rope but lacks the pegs to prevent mussel slippage. Furthermore, when mussels are grown on a flat surface, they tend to displace each other from the surface as they grow. Mussel spats may be on-grown on mussel droppers until they have reached a commercially useful size or may be harvested whilst small and then cultivated further by another technique. Mussels are harvested by removing the mussel droppers from the sea onto a harvesting vessel and then stripping the droppers of mussels either by hand (a slow and labour-intensive process) or by a machine which uses brushes to displace the mussels. In recent years, there has been substantial growth in the demand for mussels and the mussel-farming industry has struggled to keep up with demand. It is therefore highly desirable to provide techniques for increasing production volume and reducing unit costs. There is also a market for young mussels which can then be on-grown by other techniques. Therefore, it would also be advantageous to provide a better method of producing young, small mussels. US Patent 3,017,857 to Munz discloses a oyster spat collection means consisting of a fabric net and a bolt adapted to reel up and cut that net. The use of this net for oyster cultivation and subsequent retrieval onto a vessel is limited by the mechanical rigidity in a net. Such a net would be difficult in practice to reel up and would be limited in its ability to form a solid support for mussel growth. The weight of mussels can be very substantial and so mechanical strength is important if yield is not to be compromised. US Patent 3,017,857 does consider the possibility of stiffening lateral members of the net with concrete or other materials which function as an aid to the growth of oysters. However, this document does not disclose the use of any mechanically rigid structure and concrete is at present solely to aid oyster growth and preferably the net disclosed therein is cemented only at the intersections of ropes thereby not achieving significant mechanical strength. Concrete is present in US 3,017,857 simply as it benefits oyster growth and so one skilled in the art would not think to use it for mussel cultivation as mussels do not require concrete or similar materials but will grow directly on plastic ropes. It is therefore an aim of the present invention to provide a mechanically strong structure for mussel spat collection using a construction which is inherently rigid and which is cheap and easy to manufacture. According to a first aspect of the present invention there is provided a mussel cultivation means comprising a plurality of non-intersecting flexible linear support means which are joined at intervals by a plurality of spacing means characterized in that the spacing means are rigid linear support means. Preferably, the mussel cultivation means has exactly two non-intersecting linear support means. Preferably also, the flexible linear support means are plastic mussel ropes. More preferably, the spacing means are plastic overmouldings . The spacing means may be connected to other spacing means by panels wherein each panel comprises a network of linear support means upon which mussels can grow but wherein the spacing between the linear support means determines the size to which mussels grow. Typically, the spacing means extend beyond the non- intersecting flexible linear support means thereby forming teeth which may be engaged. According to a second aspect of the present invention there is provided a mussel harvesting vessel comprising a boat fitted with the mussel harvesting means adapted to harvest mussels from mussel cultivation means, the said mussel cultivation means comprising a plurality of non- intersecting linear support means which are joined at intervals by a plurality of spacing means, the spacing means being rigid linear support means, characterized in that said mussel harvesting means comprises a mussel removal means, a winching means which is adapted to reel in and store said cultivation means and a mussel conveyor means which guides the mussel cultivation means through the mussel removal means using teeth which engage with teeth engaging members. Preferably, the mussel cultivation means comprises two mussel ropes joined at intervals by plastic overmoulded spacers . Typically, the spacers extend beyond the non-intersecting flexible linear support means. The said spacers being teeth which are engaged by teeth engaging members of the mussel conveyor means. Preferably, the mussel harvesting vessel is multiply hulled with the mussel conveyor means being adapted to guide mussel cultivation means between hulls. According to a third aspect of the present invention there is provided a mussel collection system comprising a mussel cultivation means according to a first aspect of the present invention and a mussel harvesting vessel according to a second aspect of the present invention. There are now described example embodiments of the present invention with reference to the following diagrams in which: Figure 1 shows a plan view of a mussel culture track according to the present invention; Figure 2 shows a cross section through the mussel culture track of Figure 1; Figure 3 shows a vertical cross-section through a long line and a mussel harvesting vessel; Figure 4 shows a plan view of a long line and a mussel harvesting vessel; and Figure 5 shows plan and transverse cross-sections through a mussel culture track with mesh panels according to a particular embodiment of the present invention. Figure 1 shows a plan view of a mussel culture track 1 according to the present invention. Two continuous mussel ropes 2, typically made from plastic, are held by rigid spacers 3, typically plastic overmouldings, at regular intervals. Figure 2 shows the same mussel culture track in cross-section. The rigid overmoulded spacers are mechanically strong. They function to hold the two ropes apart preventing fouling and to be readily winched in by the harvesting vessel described below. It is advantageous that they are formed from an inherently strong material rather than by a multiple stage material treatment process. Furthermore, plastic overmouldings can be manufactured cheaply on a large scale making an economically viable product. Figures 3 and 4 respectively show a cross-section through and a plan of a long line and a mussel harvesting vessel according to the present invention. Two headlines 4 are supported by floats 5. From these floats, the mussel culture tracks 1 hang, held by clips 6. The mussel culture tracks are continuous - one is attached to each of the two headlines which comprise a long line. The orientation of the mussel culture tracks in the water is maintained by weighted spacers 7. A twin-hulled mussel harvesting vessel 8 straddles the line of floats and is provided on either side with a reel and winch system 9 which can dispense, retrieve or store the mussel culture track, a system of rotating brushes 10 which acts to strip mussels from the mussel culture track and a conveyor system 11 which guides the track into the brush system and transfer/storage bins 12 to store the harvested mussels. By providing two mussel ropes on each mussel culture track and a rigid spacer, the invention represents a convenient way to increase the surface on which mussels can be successfully cultured. Merely increasing the surface area by providing an extended flat surface would not be effective. This invention recognises that when mussels grow on a flat surface, they only have one outward dimension available in which to grow. They therefore displace each other from the surface as their volume increases, leading to a poor yield. When mussels grow around a linear support, such as a rope, the mass of mussels can expand in two outward dimensions, providing more space. The present invention therefore achieves its effectiveness through providing a network of linear supports. A further advantage of the configuration described here is that the spacers prevent mussels sliding down the track. A still further advantage of the ladder shape of this mussel culture track is that it can be more conveniently reeled up onto the mussel harvesting barge than a simple rope or flat sheet. For example, rollers on the conveyor system may be provided with teeth which engage the spacers. In an alternative embodiment, as shown in Figure 5, mesh panels 13 are added to the mussel culture track 1. Typically, the mesh panels and spacers will be plastic overmoulded onto the mussel ropes. This configuration will ensure that mussels grow mainly to a size determined by the pore spacing. This embodiment can therefore provide small, young mussels for on-growing further by other techniques. Although the preferred shellfish for this invention is mussels, it is clear to one skilled in the art that the same apparatus will benefit cultivation of other types of shellfish. Further modifications and improvements may be incorporated without departing from the scope of the invention herein intended.

Claims: CLAIMS 1. A mussel cultivation means comprising a plurality of non-intersecting flexible linear support means which are joined at intervals by a plurality of spacing means, characterised in that the spacing means are rigid linear support means. 2. A mussel cultivation means according to Claim 1 having exactly two non-intersecting flexible linear support means. 3. A mussel cultivation means according to Claim 1 or Claim 2 wherein the flexible linear support means are plastic mussel ropes. 4. A mussel cultivation means according to any preceding Claim wherein the spacing means are plastic overmouldings. 5. A mussel cultivation means according to any preceding Claim wherein the spacing means are connected to other spacing means by panels wherein each panel comprises a network of linear support means upon which mussels can grow but wherein the spacing between the linear support means determines the size to which mussels grow. 6. A mussel cultivation means according to any preceding Claim wherein the spacing means extend beyond the non-intersecting flexible linear support means, thereby forming teeth which may be engaged. 7. A mussel harvesting vessel comprising a boat fitted with a mussel harvesting means adapted to harvest mussels from mussel cultivation means, said mussel cultivation means comprising a plurality of non- intersecting flexible linear support means which are joined at intervals by a plurality of spacing means, the spacing means being rigid linear support means, characterised in that said mussel harvesting means comprises a mussel removal means, a winching means which is adapted to reel in and store said mussel cultivation means and a mussel conveyor means which guides the mussel cultivation means through the mussel removal means using teeth which engage with teeth engaging members. 8. A mussel harvesting vessel as claimed in Claim 7 wherein the mussel cultivation means comprises two mussel ropes joined at intervals by plastic overmoulded spacers. 9. A mussel harvesting vessel as claimed in Claim 7 or Claim 8, wherein the spacers extend beyond the non- intersecting flexible linear support means, said extended spacers being teeth which are engaged by teeth engaging members of the mussel conveyor means. 10. A mussel harvesting vessel as claimed in any of Claims 7 to 9, wherein the mussel harvesting vessel is multiply hulled, with the mussel conveyor means being adapted to guide mussel cultivation means between hulls. 11. A mussel collection system comprising a mussel cultivation means and a mussel harvesting vessel, the mussel cultivation means comprising a plurality of non-intersecting flexible linear support means which are joined at intervals by a plurality of spacing means, characterised in that the spacing means are rigid linear support means and in that the mussel harvesting vessel comprises a mussel removal means, a winching means which is adapted to reel in and store said mussel cultivation means and a mussel conveyor means which guides the mussel cultivation means through the mussel removal means using teeth which engage with teeth engaging members. 12. A mussel collection system as claimed in Claim 11 wherein the mussel cultivation means comprises two mussel ropes joined at intervals by plastic overmoulded spacers. 13. A mussel collection system as claimed in Claim 11 or Claim 12, wherein the spacing means extend beyond the non-intersecting flexible linear support means, said extended spacing means being teeth which are engaged by teeth engaging members of the mussel conveyor means. 14. A mussel collection system as claimed in any of Claims 11 to 13, wherein the mussel harvesting vessel is multiply hulled, with the mussel conveyor means being adapted to guide mussel cultivation means between hulls.

Inventors: MCLACHLAN JAMES, MCLACHLAN, JAMES
Applicants: MCLACHLAN JAMES, XPLORA PRODUCTS LIMITED, MCLACHLAN, JAMES
Application year: 2000
Main classification: A01K61
IPC codes: A01K61