WO2008067612A1

WO2008067612A1 - Spat collection and growing medium

Info

Publication number: WO2008067612A1
Application number: PCT/AU2007/001890
Authority: WO
Inventors: Peter Kvietelaitis
Original assignee: Peter Kvietelaitis
Priority date: 2006-12-07
Filing date: 2007-12-07
Publication date: 2008-06-12
Also published as: EP2094077A1; AU2007329192A1

Abstract

A mollusc spat collection and growing medium (112) including a collection and growing mesh (130) having a longitudinal axis, said mesh (130) having a plurality of transversely spaced longitudinal strands (232) extending parallel to said adjacent longitudinal axis and having spacing means (234) for spacing adjacent longitudinal strands (232), wherein the transverse spacing of said adjacent longitudinal strands (232) is substantially unaffected by application of a longitudinal load, whereby in use any spat (136) collected or growing upon the medium (112) remain transversely spaced as said spat (136) grow, thereby optimizing growing conditions.

Description

SPAT COLLECTION AND GROWING MEDIUM FIELD OF THE INVENTION

The present invention relates to an apparatus and method for use in the aquaculture farming industry, and relates particularly, though not exclusively, to apparatus which can be suspended as collection and growing lines for aquatic farming of shellfish. The invention is described herein in relation to the farming of mussels, however the apparatus and method are also suitable for use with other types of shellfish and molluscs.

This application claims priority to Australian provisional application no. 2006906844 filed 7 December 2006 in the name of Peter Kvietelaitis, the contents of which are incorporated herein by this reference thereto. BACKGROUND OF THE INVENTION

With increased demand for high quality produce, the aquaculture farming industry has developed smarter and more reliable techniques for culturing and harvesting marine life. Mussels, like other marine life, were historically harvested from the wild. However, as stocks have diminished, new methods of farming mussels have evolved. "Mussel spat" means young mussel in the post larval stage, which is usually larger than 1/3mm. They are usually measured as being up to a certain length (eg in the Tasmanian Regulations (Australia) "mussel spat" means a mussel the shell of which is less than 40 millimetres in length). A common mussel farming method now in vogue utilises collection and growing lines, such as ropes, or the like, which are suspended below the surface of the water.

A collection line or lines may be suspended below the surface of the water in order to collect seed mussels or mussel spat, which will attach themselves to the lines. Post larval juvenile seed mussels or mussel spat collect on these lines and as they grow form dense clusters, in fact a density which is too large to allow the mussels to mature properly. At this point a mussel farmer may withdraw the collection lines from the water to perform density adjustment, by separating, de- clumping, grading and injecting the immature mussel spat into a mesh sleeve, sock, net or the like, which can sometimes surround a growing line. To perform these operations the spat must have reached sufficient size while growing on the collection line. Polypropylene ropes having a diameter of 12 to 16 millimetres are commonly used as a collection (or as a growing) line. They have positive buoyancy, which must be offset by addition of weights to ensure the line sinks and is suspended from a supporting line, rather than floating. This helps prevent entanglement of the collection (or growing) line around the supporting line in adverse weather conditions. Use of a rope of larger diameter is impractical due to the increased weight and volume for manual handling, increased cost and increased buoyancy which must be offset by further weights.

"Sleeving" or "socking" is the operation by which seed mussels or mussel spat are loaded at a particular density (Je, number per unit length) into a mesh sleeve or sock, which (usually) surrounds a central growing line, to be returned to the water for further maturation. A sock is a long mesh tube commonly knitted of cotton and often strengthened with a strand of polypropylene twine. Individual socks are about 40mm in diameter and may typically average 2.5 - 3.0 metres in length depending on local water depths when used with dropper line systems. The socking process facilitates mussel attachment to a growing line at a more appropriate density to assist the growth of mussels when they are re-introduced into the water. The sock initially supports the mussels so that they can attach to the growing line. As the mussels increase in size, they attach to and their weight is supported by the growing line. Over time, mussels grow and migrate radially outwardly from the growing line, and through the mesh sock which may degrade or disintegrate over time. A mature mussel can be several inches long.

The term 'collection line' is used to refer to a line used to initially collect the post larval juvenile spat but it is noted that a 'collection line' then supports these spat as they grow, hence functioning as a 'growing line'. The same or similar line may also be used in the post-socking stage as a 'growing line'. Hence the function of the collection or growing line should be taken in context of the stage of growth of the spat.

An alternative growing medium is use of a non-perishable polypropylene mesh tube or netting having diamond shaped mesh spaces. Mussel spat are loaded into the non-perishable mesh tube at a particular density (Je, number per unit length). This may remove the need for a separate rope growing line with socking mesh. The spat grow and migrate from internal positions (Ze, inside the tube) through the mesh spaces to external positions (Ze, outside the tube).

As mussels increase in size they migrate. The mussels closest to the growing line are attached to and rely on support from the growing line itself. The mussels disposed radially outwardly rely on attachment to other mussels for support. If a perishable cotton sock is utilised, mussels in the vicinity of the sock can initially also rely on this sock for support. After the sock disintegrates, mussels in that vicinity can only rely on support from those mussels beneath them (Ze, in a lower position on the growing line) or radially inward from them. It is at this point that the entire mussel crop is reliant on the foothold of those mussels (the supporting mussels) that have directly attached themselves to the growing line. The number of mussels that can safely attach themselves directly to a growing line is dependant on the surface area (Ze, diameter) of the growing line itself. As mentioned above, it is not practical to significantly increase growing line diameter above a certain level. It thus become evident that, as mussels grow and hence weight increases, if supporting mussels lose their foothold significant losses of crop can occur as large clusters of mussels fall away from the growing line. It is noted that the bonding (byssal attachment) of a mussel to a polypropylene rope has less strength than the bonding to another mussel. Hence failure occurs between foothold or supporting mussels and the rope (resulting in loss of all mussels) rather than between adjacent mussels.

Furthermore, as heavily laden mussel growing lines are immersed in water, the water itself serves to create a buoyancy effect supporting the mussels that are attached to the growing lines. However during the harvest the mussel growing lines are lifted out of the water, meaning this supporting buoyancy effect is lost. This loss of support means the full weight of the mussels needs to be self- supporting on the collection (or growing) line, and can result in a significant increase in the losses associated with mussels falling away from the lines at the time of harvesting, in addition to any losses suffered during the growing period. Losses associated with mussels peeling off or falling away from growing lines will hereinafter generally be referred to as the "slide off effect".

Issues relating to the slide off effect and apparatus and method for partially alleviating this problem are disclosed in PCT application No. PCT/AU2005/001238, published as WO 2005/025307A1 , in the name of Peter Kvietelaitis, the contents of which are incorporated herein by this reference thereto. Traditionally, the "slide off effect" is dealt with by the attachment of support structures to the growing line, which is usually a rope. In commercial mussel harvesting operations, there are two main forms of collection and growing lines. In a dropper line system, a plurality of collection or growing lines may be suspended below the water surface from a support structure, such as a buoy or another line. This support line may be attached at either end to buoys, or be otherwise supported. In a continuous line system, a single collection and growing line is supported to form loops suspended below the water surface, usually from a support line.

Due to the negative environmental consequences associated with using a large net as a supporting medium for collection and growing of mussels (as marine animals such as dolphins may become entangled in such nets), it is preferable to use the growing line method. In general, marine animals such as dolphins are freely able to swim between growing lines without becoming entangled therein, even where a relatively high density of growing lines are located. The growing line method also has the positive effect of reducing any interruption to growth and production, or slide off effects, that may be caused by the entanglement of marine animals in the net.

An advantage of using a growing line method is the ease with which the growing medium may be handled. For example, in a dropper line system each growing line may be detached from the supporting structure, harvested and dealt with independently of other lines. Reduced weight in handling a single line makes growing lines a preferred option. Growing lines may also be adjusted and/or rotated if desired under particular circumstances. In a continuous line or loop system, productivity gains in terms of mechanical continuous handling of a single line can be made, however this results in substantial increases in crop losses (Ze, decreased yield) due to the slide off effect. In some circumstances, crop loss will negate the productivity gain.

There is however an inherent problem with use of a rope as a growing line, or a rope having an associated sock or sleeve, whether a dropper line system or continuous line system, in that the supporting rope provides a limited surface area to which mussel spat may attach. Additional mussel spat must rely upon the mussels below or radially inward for support and result in the above mentioned slide off effect. Further, use of a rope may result in undesirable clumping, wherein mussels on the inside of the clump do not receive adequate water flow or nutrients and hence result in a size disparity with outer mussels. The time to crop maturation increases as most of the mussels must reach a minimum size before harvesting.

Immature or juvenile mussel spat typically collect on collection lines at a density that is too great to permit growth to maturity of the mussels. Hence, there is a need for a farmer to withdraw spat collection lines from the water for density adjustment by separating, de-clumping, grading as to size and injecting the immature mussel spat into a sock for further maturation on a growing line. This obtains optimal growth and mussels of relatively even size or maturity, which is highly desirable from a production and a marketing perspective. Purchasers expect to receive graded sizes and quality of mussels and the grading process is desirably carried out upon immature mussels, since density adjustment of the immature mussels will maximise growth and minimise production time. If the immature mussel are not graded as to size, the resultant crop will not be of even size. The de-clumping and grading of mussel spat is an onerous task, which cannot be carried out until the spat have grown to at least a size that permits meaningful grading.

It is desirable to provide a spat collection and growing medium which facilitates collection and growth of spat, at an appropriate density, while enabling any necessary density adjustment to be performed as early as possible such that optimal growing conditions are provided, while reducing the labour involved in socking mussel spat.

It is also desirable to provide a spat collection and growing medium that provides an optimal growing environment so as to enhance growth rates. It is further desirable to provide a spat collection and growing medium that increases yield and reduces "slide off effect". It is further desirable to provide a spat collection and growing medium of reduced weight, volume, cost and buoyancy when compared to prior art mediums, and of increased ease of handling. SUMMARY OF THE INVENTION A first aspect of the present invention provides an improved mollusc spat collection and growing medium including a collection and growing mesh having a longitudinal axis, said mesh having a plurality of transversely spaced longitudinal strands extending parallel to said adjacent longitudinal axis and having spacing means for spacing adjacent longitudinal strands, wherein the transverse spacing of said adjacent longitudinal strands is substantially unaffected by application of a longitudinal load, whereby in use any spat collected or growing upon the medium remain transversely spaced as said spat grow, thereby optimizing growing conditions.

In a preferred embodiment said spacing means includes a plurality of longitudinally spaced transversely extending strands intersecting said longitudinal strands, to form a plurality of mesh spaces.

Preferably said transversely extending strands are stiff and are permanently fixed to said longitudinal strands at each intersection between said transverse strands and said longitudinal strands. Preferably each of said plurality of mesh spaces is rectangular or each of said plurality of mesh spaces is square. Preferably the strands are plastic or polypropylene.

Preferably the collection and growing mesh is a tube and preferably the strands are a thread ply, tubular or a ribbon. Preferably the longitudinal strands remain substantially of constant length when longitudinally loaded and preferably said growing mesh is resilient. The medium may further including a longitudinal rope.

Preferably, the medium further including restraining means for restraining said growing mesh in a furled position, which may be a ring or an aquaculture support device or may be a sock for substantially enclosing said growing mesh in the furled position, said sock being a knitted sock or having a plurality of diamond shaped mesh spaces. Preferably each of said mesh spaces is a square of between 5 to 50mm x 5 to 50mm, preferably of between 10mm to 30mm x 10mm to 30mm, more preferably of 25mm x 25mm. When the medium is used for spat collection preferably the mesh spaces are 7mm x 7mm. A second aspect of the present invention provides for use of a mollusc spat collection and growing medium according to a first aspect of the invention in the collection or growing of molluscs.

A third aspect of the present invention provides for use of a mollusc spat collection and growing medium according to the first aspect of the invention in a method of farming molluscs, the method including the step of socking spat either internally or externally of the growing mesh.

A fourth aspect of the present invention provides a mollusc farming method including the steps of: providing a spat collection and growing medium according to the first aspect of the invention; allowing spat to collect upon said medium and grow into juvenile molluscs; stripping the juvenile molluscs from the medium; adjusting the density of said juvenile molluscs; and allowing the adjusted juvenile molluscs to grow to maturity. Preferably, density adjustment is performed by socking the stripped molluscs.

In one preferred embodiment the collection and growing mesh is provided as a tube, which is preferably of continuous mesh. The continuous mesh tube is preferably supplied in a flattened or belt form upon a roll, for continuous dispensing. The flattened belt may be expanded back to a tube, and the continuous length may be cut as may be required for a specific application.

In another preferred embodiment, the collection and growing mesh is provided as a substantially planar sheet, which is preferably of continuous mesh. The continuous mesh is preferably supplied upon a roll, for continuous dispensing. The continuous length may be cut as may be required for a specification application. The tube or sheet can be furled as tightly or loosely as required. The term furl and its variants as used herein are used to indicate that, for example, a typically planar collection and growing mesh is positioned in an elongate, or tubular, form. Furling may be achieved in many ways including, but not limited to, rolling, scrunching, concertina or folding together, drawing, curling, twisting, bending, or coiling the collection and growing mesh. A tubular growing mesh can also be furled, constricted or compressed by distorting the circumference of the tube.

Furthermore, the collection and growing medium can include a number of mesh layers, which may be furled together or otherwise arranged. A collection and growing medium may be used for collecting spat.

Collected spat will then grow upon the medium until they are stripped from it. The collection and growing medium may also be used as a medium for growing spat, eg after the socking operation. Hence, a collection and growing medium may be used for collection, or growing, or both. Advantageously, a mollusc spat collection and growing medium according to the present invention allows for more uniform collection and growth of mussel spat into juvenile mussels. The uniform growth of mussel spat upon the collection and growing medium permits aquaculture farmers to sock spat much earlier in the season, with reduced grading requirements, significantly reduces the need to declump (i.e. separate one mussel from being attached to another mussel) and thereby reduces or eliminates the stress suffered by mussel spat during the density adjustment and socking operations. This results in improved size quality and product quality at harvest and shipping.

Spat which are located underneath or 'inside' a clump of mussel spat (e.g. attached to a rope) struggle to obtain the food required and have a poorer growth environment than the spat on the 'outside' of the clump of spat. The 'outside' spat typically have better growing conditions and higher food availability, resulting in larger sized mussels on the 'outside', at an earlier age, which are preventing the 'inside' spat from receiving nutrients and hence retarding their growth. This in turn results in the need to grade the spat according to size before adjusting density by socking.

In the prior art, the mussel spat collected upon a growing line need to be declumped, graded and then socked in order to adjust the density. The mussels must then reattach to a central growing line, before the mesh sock disintegrates. This causes stress to the spat, as well as using time and energy that could have been put into increased growth.

Once the larvae / spat grow to a certain size, density adjustment needs to be carried out in order to ensure a beneficial environment. Any spat below a certain size may be lost in the grading process and hence it is necessary to wait for the majority of the crop to be over this size before commencing. Hence, in the prior art, larger mussels were left to remain in sub-optimal conditions before grading and density adjustment could commence, as too many smaller mussels were below the minimum size and farmers must wait for them to grow, while these smaller mussels were left to remain in sub-optimal conditions with poor nutrient levels. The present invention ensures that due to the even size of a crop, density adjustment and any necessary grading can commence much earlier and hence the mussels are provided with optimum conditions for a longer period. This results in larger mussels, or a shorter growing cycle, and hence increased efficiencies.

The collection and growing medium mesh strands provide intersections and mesh spaces. As mussel larvae / spat attach to the strands and intersections, the mesh space ensures that attachment density in a given area is not too high - due to the open space where spat cannot attach, average density of spat is low. This ensures the spat all receive good water flow / circulation through the open spaces and hence high levels of nutrients, for optimal growth.

By having a furled or tubular collection and growing mesh, a 'tube' having a large "surface area" (which includes the open mesh spaces) is created - an area far larger than the surface area of a prior art growing rope. Hence, the mesh can carry the spat at a lower average density than a rope could. Furthermore, when used a collection medium, water circulates both 'inside' the 'tube' as well as through the open mesh spaces and 'outside' the 'tube'. This results in spat receiving similar nutrition, even when some clumping does occur. The mesh can be removed from the water and the spat density adjusted by socking, but grading of spat is minimised or elimated as 'inside' mussels have grown at approximately the same rate as 'outside' mussels. In prior art mediums using a rope as the growing line, in a given time period, if nutrients are supplied differentially to some spat e.g. 'outside' spat, spat growth will be uneven, with some spat growing much larger than others. Unfortunately, it is necessary to then wait additional time for the smaller spat to grow to minimum size before grading, density adjustment, and socking can take place, otherwise the small spat are lost during operations and the eventual harvest crop reduced in number. However, if in the same given time period, nutrients are supplied relatively evenly (as in the present invention), spat will grow evenly and the majority will be of sufficient size to be density adjusted and socked at the end of the period. Thus, density adjustment and socking can take place earlier than in the prior art, as no additional waiting for undersized spat to grow is required to avoid loss.

The ability to adjust the density of mussel spat (i.e. to sock spat) when the spat are at an average smaller size with each spat just large enough to sock provides quality improvement as the spat are enabled to grow in optimal density conditions for a longer period. This can also allow aquaculture farmers to take full advantage of the beneficial warmer water season.

The present invention stems partially from the realisation by the inventor that maintaining the transverse spacing of collected spat, even as the juvenile spat increase in size and weight to a sockable size, is important to ensure optimal low density conditions and optimal growth while the newly collected spat increase to minimum sockable size.

As weight supported by a collecting or growing line increases, the longitudinal load applies longitudinal forces. Where the longitudinal load is not carried by a longitudinal member, such as a rope, these forces tend to distort the load carrying members. Hence, as shown in Figures 5b and 5c, a longitudinal load applied to a prior art 'diamond' shaped mesh results in elongation of the diamond such that transverse spacing is not maintained, referred to hereinafter as "collapsing" or constricting of the mesh. As weight increases, the non- perishable mesh tube constricts and elongates due to its diamond mesh space geometry, becoming "rope like". This constriction also forces any remaining internally positioned spat or mussels to move to external positions. The rope like constricted mesh tube may have an external diameter of less than 10 millimetres. In contrast, as shown in Figures 5a and 5d, the longitudinal load does not distort the collection (and growing) medium according to the present invention.

In the present invention, longitudinal load is carried by the longitudinal strands of the medium and transverse spacing is largely unaffected by loads expected in mussel farming. The medium is geometrically stable in the longitudinal direction under longitudinal load. Preferably, the mesh has even, square mesh spaces and is woven or otherwise made of a stiff plastic such as polypropylene that will not degrade before the growing season is completed. Preferably the mesh has stiff transverse strands to assist geometric stability. Of course, a carcass reinforcement of longitudinal threads may be used to alter the geometry of a 'diamond' netting, with the load largely being carried by the reinforcing carcass, or a square mesh could be encased in a knitted sock, diamond mesh or other combination. Where a particular optimal spacing is required or desired for particular conditions or spat size, the degree of furling of the collection and growing medium can be adjusted by use of an appropriate restraining means. Suitable restraining means include a ring, an aquaculture support device or a sock. It is desirable to restrain a planar mesh in a furled position because it will provide an elongate growing line which is unlikely to become entangled with an adjacent growing line and which is unlikely, for example, to trap marine animals such as dolphins, even when a large number of growing lines are suspended in a particular area of water. Where the collection and growing medium is a tube, the tube may be provided at a particular required diameter, or may itself be furled as required using an appropriate restraining means. Where a sock is used as a restraining means it can serve to hold recently socked spat in position, as well as to constrict or compress the growing mesh in the furled position. By varying the sock used, the growing mesh may be compressed (restrained or furled) to a different degree, to suit the particular growing conditions, size or type of spat or other variable. Hence, rather than varying the size of mesh spaces in order to obtain a particular spat density, a given mesh space size of the furled mesh may be compressed by the sock. The sock may be a knitted cotton sock. Alternatively, a second mesh could be used as restraining means in a similar manner to a knitted cotton sock, the second mesh having diamond mesh spaces (or other mesh spaces). Where the second mesh has diamond, ellipse or other shape likely to 'collapse' or 'restrict' under longitudinal load, it will, similarly to a knitted sock, tend to restrain or restrict the furled collection and growing mesh as longitudinal load is applied to it. The longitudinal load could be a weight attached to the growing line, or could be simply that of the spat that becomes attached to the second mesh, as spat will take advantage of any available foothold. The square (or rectangular) mesh growing medium encased by such restraining means resists collapse caused by spat loading, due to its longitudinal strands, and although is compressed by the diamond mesh eg to hold recently socked spat onto the growing medium, it may also resist collapse caused by the restraining means due to its preferably stiff transverse strands. Hence, an elongate growing line may be created to provide the desired spat density. When socking spat, a knitted sock could then be used to encase the growing mesh and second mesh, to ensure that small spat that would otherwise fall through the second mesh are held against the growing mesh until they have attached thereto.

When the furled or tubular mesh is used as a growing medium or mesh onto which mussel spat are socked, water may circulate both 'inside' the 'tube' as well as through the open mesh spaces and 'outside' the 'tube', depending on how the mussel spat are socked.

If the spat are socked 'outside' the 'tube', ie externally of the growing mesh, and held in place by a sock, water may circulate 'inside' the 'tube'. If the spat are socked 'inside' the 'tube', ie, internally of the growing mesh, water is less likely to circulate 'inside' the 'tube'. The spat are optionally held in place by a sock.

Mussel byssal threads can attach to the mesh or extend through the mesh to attach to a mussel on the other side, whether to an internally positioned mussel, or an externally positioned mussel located at another point on the external circumference of the tube. Mussel byssal attachment to another mussel is generally stronger than to materials such as polypropylene. Hence, attachment of some 'external¹ mussels, through the mesh and to another mussel provides a stronger attachment or foothold and reduced slide off effect.

The socking of spat 'outside' or externally of the growing medium assists with obtaining even growing, shorter time periods due to the improved water circulation and reduced clumping. However, if it is desired to increase yield, ie, number of mussels, rather than improving growth rate or obtaining even sized mussels, the spat may be socked internally of the growing medium, ie, 'inside' the 'tube'. This trade off depends on local environmental and market conditions.

Socking spat internally of the growing medium will result in a secure core of spat bonded to each other and the growing medium. Spat grow and migrate radially through the medium to external positions, but the increased weight of mussels does not result in constriction of the growing mesh. Therefore, many of the spat remain in the centre to form a core, as they are not forced to an external position by constriction of the growing mesh, which is what occurs when diamond mesh is used. A strong central core structure or column of mussels attached to each other is obtained, with mussel byssal threads extending through the mesh, and attaching to other mussels. The central core of mussels is securely held internally by the medium and is not subject to slide off effect, while external or migrated mussels are attached to each other and the central core mussels rather than to a rope, with a stronger bond. They are not reliant on a supporting mussel having a foothold on a polypropylene rope. Furthermore, as a larger surface area is provided, the mussel density is still reduced when compared to a traditional rope system.

Where a very heavy load is applied to a collection and growing mesh with 'square' or 'rectangular' mesh spaces, a tubular mesh may contract from circular cross-section to an oval, or in extreme cases to a flat 'belt'. However, the lateral and vertical spacing of mesh spaces is substantially maintained and the circulation of water and nutrients through the mesh spaces and outside the 'tube' provides better growing conditions than a rope. Furthermore, the same number of mussels can be carried on the mesh at a far lower average density than a rope, even when contracted into a belt.

A spat collection and growing medium according to the present invention may have the advantages of providing an increased surface area for spat attachment and hence low density spat spacing, of resisting collapse and hence maintaining spacing and low density as a longitudinal load is applied, of providing improved water and nutrient circulation to the spat, of increasing yield and reducing slide off effect (through enabling stronger bonds, eg of mussels on opposite sides of the medium, and through increased area for mussel footholds) and of providing a light, strong, flexible and easy to handle medium that is easily stored and transported, even on a moving boat.

Importantly, density adjustment of collected spat may be performed earlier, due to the even crop size obtained by the low density conditions and the reduction of spat clumping. Hence, each spat, on average, is socked at a smaller size.

Another advantage of the present invention is that the weight and volume of a rope is far greater than for equivalent growing mesh. This results in easier handling, particularly upon a boat. Furthermore, use of weights to counter buoyancy of the medium is reduced, as the medium has less material than an equivalent rope and hence less weight is required to counter its buoyancy.

Further preferred aspects of the apparatus & method may be as defined in the dependent claims annexed hereto, which claims are hereby made part of the disclosure of this invention. BRIEF DESCRIPTION OF THE DRAWINGS

Other features and advantages of one or more preferred embodiments of the present invention will be readily apparent to one of ordinary skill in the art from the following written description with reference to and, used in conjunction with, the accompanying drawings, in which: Figure 1 is a side view of a molluscs culture growing arrangement according to a preferred embodiment of the invention showing growing lines suspended beneath the surface of the water in order to provide support for molluscs as they grow; and

Figure 2 is a perspective view of molluscs attached to each other and a support via byssal thread attachment; and

Figure 3 is a cross sectional view of a prior art growing line and sock; and Figure 4 is a cross sectional view of a growing line including a spat collection and growing medium according to a preferred embodiment of the present invention; and

Figures 5a and 5d are perspective views of a tubular spat collection and growing medium according to another preferred embodiment of the invention; and

Figures 5b and 5c are perspective views of a tubular prior art diamond mesh; and

Figures 6a and 6b are a perspective view and a cross sectional view of a growing line including a spat collection and growing medium according to another preferred embodiment of the invention; and

Figures 7a and 7b are a perspective view and a cross sectional view of a spat collection and growing medium according to another preferred embodiment of the invention; and

Figure 8 is a partial cross sectional view of a socking process using a spat collection and growing medium according to another preferred embodiment of the invention; and

Figure 9 is a partial cross sectional view of a socking process using a spat collection and growing medium according to another preferred embodiment of the invention; and Figures 10a and 10b are cross sectional views of a spat collection and growing medium socked using the process shown in Figure 8, after socking, and after allowing time for mollusc growth; and

Figure 11a and 11 b are cross sectional views of a spat collection and growing medium socked using the process shown in Figure 9, after socking, and after allowing time for mollusc growth; and

Figure 12 is a side view of a spat collection arrangement according to a preferred embodiment of invention; and

Figures 13a and 13b are cross sectional views of a prior art collection rope line, at spat collection stage, and showing growth of the spat prior to socking; and Figures 14a and 14b are cross sectional views of a collection and growing line including a spat collection medium according to a preferred embodiment of the invention, at spat collection stage, and showing growth of the spat prior to socking. DESCRIPTION OF PREFERRED EMBODIMENT Growing Molluscs - Overview

Shown in Figure 1 there is a mollusc growing arrangement 10 according to a preferred embodiment of the invention suitable, for example, for growing mussels. Mollusc growing arrangement 10 includes a plurality of growing lines 12 adapted to be vertically suspended below the surface of the water 14 to provide a series of collection and growing media for mollusc cultivation. Growing lines 12 are suspended from a substantially horizontal support line 16. Support line 16 is suspended beneath the water surface 14 between a pair of buoys 18. Two substantially vertical support lines 20, 22, each anchored to the seabed 24 at anchor points 26, 28, are attached to respective buoys 18 in order to maintain the overall mollusc growing arrangement 10 at a chosen location. Weights 13 are attached to the ends of lines 12. The lines 12 are each restrained in a furled position, using a restraining means. In the embodiment shown in Figure 4, the restraining means include a knitted mesh sock 142. Optionally a restraining ring 144 may be used, as shown in relation to the embodiment of Figure 12. Collecting Juvenile Mollusc Spat - Overview

Figure 12 shows a similar mollusc collection arrangement according to a preferred embodiment of the invention, suitable for the initial collection of mussel spat. In this embodiment, a restraining ring 144 is shown, for restraining lines 112 in a furled position. Alternatively, a restraining sock could be used. The restraining ring 144 may optionally serve as a weight which may reduce the need for a separate weight 113 attached to the end of the line 112. The collection and growing medium forming growing line 112 is placed in the water in the right season. Fertilised mussel eggs become swimming larvae and remain so for approximately three weeks. The larvae then change to shelled form of approximately 1/3 mm in length and develop a foot. The mussel spat 136 secrete a cement thread (byssal thread) from this foot to attach to a structure and secrete further threads until securely attached. Smaller mussels can still move around by moving the foot and slowly attaching further along - hence they can 'migrate' toward nutrient sources. This is more difficult for larger mussels. After a further period (for example, three weeks), the spat become visible and after various processes they are eventually harvested for consumption at about one year of age.

Figure 2 shows the way in which mussels 36 may attach to a support 35 or to each other via byssal threads 37.

Structure of the Spat Collection and Growing Medium

The structure of the spat collection and growing line 112 including the spat collection and growing medium is shown in Figures 6a and 6b, in which the furled collection and growing mesh 130 has been exposed or partially unfurled at one end. The mesh 130 has a longitudinal axis, parallel to which longitudinal strands

232 extend. Adjacent longitudinal strands 232 are transversely spaced apart by spacing means, being transversely extending strands 234. The longitudinal strands 232 and transversely extending strands 234 intersect at intersections 235 to form a plurality of mesh spaces 233. In alternative embodiments, other forms of spacing means could be used.

In the preferred embodiment shown, the longitudinal strands 232 and transversely extending strands 234 are fixed to each other at each intersection 235, each intersection 235 forming a corner of a square mesh space 233.

Longitudinal load applied to the spat collection and growing line 112, eg the weight of growing mussel spat, will be 'carried' by the longitudinal members

(Ze, longitudinal strands 232). Adjacent longitudinal strands 232 remain transversely spaced apart, which in turn ensures that spat attached to the strands also remains transversely spaced and hence in a low density arrangement.

Attempts have been made in the past to use a knitted sock as a collection or growing medium. However, a knitted sock is not in general strong enough to support the weight of mussels likely to grow upon a sock and therefore the sock may itself break when it is attempted to be brought out of the water for harvesting or any intermediate process. This is why, in general, a central growing rope is used, in order to provide strength to the growing line. Furthermore, and importantly in contrast to the present invention, a knitted sock contracts 'like a string bag'. A knitted sock or "diamond" pattern mesh, under longitudinal load, will collapse, that is will contract transversely and elongate longitudinally such that the area of the mesh spaces is reduced and hence the spat density increased, as the spat increase in size. This effect is shown in Figures 5b and 5c, in which Figure 5b has no load and Figure 5c is longitudinally loaded, thereby transversely contracting and longitudinally elongating. Similar effects occur with the knitted mesh socks, where the stretch nature of a knit causes distortion of the mesh under longitudinal loading. The diameter d1 of the unloaded mesh is reduced under load to the smaller diameter d2.

In comparison, and as shown in Figures 5a and 5d, a collection and growing medium 130 according to the present invention does not collapse under longitudinal load. It has longitudinal strands 232 and transversely extending strands 234 which intersect at intersections 235 to form a plurality of mesh spaces 233. The spacing between adjacent longitudinal strands 232 is substantially unaffected by application of a longitudinal load. Preferably, the transversely extending strands 234 are stiff and hence assist in resisting collapse under load. The longitudinal strands 232 and transversely extending strands 234 may be woven or simply cross, however by fixing the strands 232, 234 at each intersection 235 (rather than a non-fixed weave) the risk of mesh distortion under load is further reduced. The longitudinal strands 232 and transverse strands 234 of mesh 130 are of polypropylene and are fixed to each other at intersections 235 by plastic welding.

The collection or growing medium according to the present invention is advantageously a polypropylene plastic mesh having longitudinally and transversely extending strands forming square mesh spaces of a suitable size. Preferably each said of mesh spaces is a square of between 5 to 50mm x 5 to 50mm, preferably of between 10mm to 30mm x 10mm to 30mm, more preferably of 25mm x 25mm. In one preferred embodiment, the size is approximately 7mm x 7mm.

Preferably the growing mesh is a plastic mesh which is sturdy and has resilient properties that allow for sudden load change, e.g. during the process of retrieving the medium from the water, as well as having good tensile strength.

Figures 7a and 7b show a collection and growing line 112 which further includes a sock 142. The mesh sock 142 has a "diamond" mesh pattern and surrounds the planar mesh 130, acting as a restraining means to hold the planar mesh 130 in a furled position. The mesh sock 142 may collapse around the planar mesh 130 as load is added, but is resisted by the stiff transversely extending strands 234.

Alternatively, a fine meshed knitted sock could be used to hold the partly grown spat against the growing mesh, the spat being trapped between the opposing forces of restraining sock and the collapse-resistant growing mesh. This prevents spat from falling off the growing medium and being lost into the water. A diamond mesh of larger diameter could additionally be provided, and as the spat increase in weight and attach to both square growing mesh and diamond restraining mesh, the knitted sock may rot away but the growing mesh is still restrained by the diamond mesh as it elongates and constricts under the longitudinal load.

The collection and growing medium according to the present invention may be a planar sheet as shown in Figures 6a to 7b, or may be in a tubular form. From Spat Collection to Density Adjustment

As shown in Figure 12 and in the cross section views of Figures 14a and 14b, the collection line 112 includes a collection and growing medium being a planar collection and growing mesh 130, furled with restraining means 140 to form an elongate collection and growing line 112. The restraining means 140 is a mesh sock 142.

The collection line 112 including the collection medium (mesh) 130 may be used to collect spat 136. The juvenile spat 136 are collected upon collection line 112 and particularly on collection mesh 130 and then grow until they are large enough to be density adjusted and socked. The seed collector lines (collection line 112) allow good water and nutrient circulation, which ensures optimal spat growth and an evenly sized crop.

Figures 13a and 13b show the stage of initial collection of juvenile spat 136 onto a prior art collection rope 30, and the stage at which spat 136 are ready for density adjustment, noting the uneven sizes of the outside spat 136 and inside spat 136a. Unlike the spat 136 of Figures 14a and 14b, the spat of Figures 13a and 13b will require substantial declumping and size grading operations before they can be socked and returned to the water for further maturation. Figure 14a shows the stage of initial collection of juvenile spat 136 and

Figure 14b shows the stage at which spat 136 have evenly grown and are ready to be density adjusted, with minimal declumping or grading required. Each spat

136 has been able to attach to collection mesh 130 rather than relying upon foothold mussels and incidence of slide off effect is therefore low.

Juvenile mussels 136 have collected upon, attached to and grown upon the collection and growing mesh 130. Because the collection and growing mesh 130 has a much larger surface area than a prior art collection or growing rope 30 (such as that shown in Figures 13a and 13b), each of the spat 136 shown in Figure 14b is able to attach directly to the growing mesh 130, rather than attaching to each other as shown in Figure 13b. This assists in reducing the incidence of slide off of clumps of mussels, as each mussel in general supports only its own weight and not that of an attached clump of mussels.

Spat 136 collect and grow upon and are relatively evenly spaced upon the collection and growing medium (mesh 130) as they can attach only to longitudinal or transverse strands of the mesh and not to the vacant mesh spaces.

When the spat 136 grow to a suitable size, and/or the density of the spat 136 becomes too high for optimal growing conditions, the growing line 112 may be withdrawn from the water with relatively low risk of slide off effect, and the spat stripped from the furled collection medium. Spat will tend to migrate towards the best nutrient location, which is the outside of the furl, although additional nutrients are also available on the inside of the furl, unlike a prior art rope.

In the prior art, where juvenile mussels were collected on a collection rope, it was necessary to strip (remove) all mussels, declump them from each other and grade them for size, as the size of mussels on a prior art line varies considerably.

Mussels to the inside of a clump typically have had less access to food/nutrients and thereby have not grown as well as other mussels, causing size variation.

Using a collection and growing medium according to the present invention, mussel spat are collected at a lower average density, (due to the increased effective surface area of the mesh) thus they are less likely to form clumps in comparison to using a prior art collection and growing rope. A relatively even size of mussels is obtained (as mussels generally have similar access to nutrients) and therefore it becomes less likely that significant de-clumping or grading will be required when performing density adjustment and socking.

The present invention provides a significant reduction in required time and labour, in that declumping or grading of the mussels is minimised or eliminated. Further, the mussel spat have, on average, suffered significantly less shock and better growth in a shorter period is obtained as a result.

In prior art mediums using a rope as the collection or growing line, in a given time period, if nutrients are supplied differentially to some spat e.g. 'outside' spat, spat growth will be uneven, with some spat growing much larger than others. Unfortunately, it is necessary to then wait additional time for the smaller spat to grow to minimum size before grading, density adjustment, and socking can take place, otherwise the small spat are lost during operations and the eventual harvest crop reduced in number. However, if in the same given time period, nutrients are supplied relatively evenly (as in the present invention), spat will grow evenly and the majority will be of sufficient size to be density adjusted and socked at the end of the period. Thus, density adjustment and socking can take place earlier than in the prior art, as no additional waiting for undersized spat to grow is required to avoid loss. Furthermore, on average, each spat can be density adjusted, or socked, at a smaller size, being the minimum sockable size. As it is not necessary to grade the crop for size, these small spat are not vulnerable to the losses suffered among small spat in a typical grading operation.

As the spat removed from the collection and growing mesh typically will not require significant declumping or grading, they may quickly and easily be passed directly to the density adjustment and socking operation, preferably being positioned upon a growing mesh similar in nature to the collection mesh and assisted to adhere to the growing mesh by the restraining presence of a knitted sock.

In practice, it is envisaged that identical collection and growing mediums may be used for both the collection and initial growing of spat, and the growing and further maturation of density adjusted spat. Of course, these mussel spat may also be socked in a traditional socking arrangement with a growing rope and sock, as is known in the prior art. Socking and Growing Spat to Maturity

Prior art growing ropes are similar to prior art collection ropes. Figure 3 shows a cross sectional view of a prior art growing rope 30 onto which mussels 36 have been socked using mesh sock 32. The mussels 36 have started to attach to the rope 30 and to each other via byssal threads 37.

A mesh sock is usually of about 40 millimetres diameter and is knitted for ease of manufacture. The sock can be knitted into a variety of patterns, including "square" and "diamond" shapes.

A tube of 40 millimetre diameter made of industry standard materials such as cotton, as are generally used for this purpose, does not have sufficient strength to support (for example) a two to four metre length of mature mussels growing thereupon. If so used, as mussel weight increases, the mesh sock elongates, or stretches such that the "tube" is more akin to a rope. The sock perishes or rots and crop loss becomes likely. Preferably, a central rope is provided for the mussels to attach to, and provides the strength of the growing line. However, there is a high incidence of slide off effect when ropes are used.

In the aforementioned application PCT/AU2005/001238 there is shown attached to growing lines and positioned at spaced-apart locations thereon a plurality of aquaculture support devices which reduce the incidence of slide off effect. The aquaculture support devices are embodied as support structures which are adapted to provide additional support for mussels to attach to, as they grow. In the harvesting operation, when aquaculture devices have been attached to growing lines and placed in the water environment mussels are not only able to attach themselves to other mussels, growing ropes and mesh sock, but can also attach themselves to aquaculture support devices for additional support. Aquaculture support devices provide platform-like supports for mussels that radiate from the vertically suspended growing lines. This platform-like attachment of mussels helps to reduce losses associated with the slide off effect.

However, such devices are inconvenient for handling purposes and, while they can increase crop yield, cannot improve crop quality or promote even growth.

Figure 4 shows a growing line 112 according to a preferred embodiment of the invention, on which spat 136 have been socked. The growing line 112 includes planar collection medium or mesh 130, which has been furled into an elongate line 112.

The growing line 112 of Figures 6a to 7b may be used for spat collection or for growing spat. As shown in Figures 8 and 9, to prepare line 112 in order to use a spat collection and growing medium according to the present invention in the socking operation, a planar sheet 130 of growing mesh may be dispensed from a roll 350, fed past guide 360 and through the centre of cartridge 370. Cartridge 370 is loaded with sock 142, which is dispensed onto line 112 as the furled mesh 130 is drawn through the cartridge. Spat 136 are loaded onto line 112 via funnel 375. In Figure 8, the spat 136 are loaded 'outside' the furled mesh 130 and are held in place by sock 142, which also acts as a restraining means to maintain the mesh 130 in a furled position. In Figure 9, the spat 136 are loaded 'inside' the furled mesh 130, and any spat 136 that escape to 'outside' the furled mesh 130 will be held in place by sock 142, which again acts as a restraining means. Figure 10a is a cross section view taken from Figure 8, and Figure 11 a is a cross sectional view taken from Figure 9.

In Figure 10a, the socked spat 136 have been loaded onto the 'outside' of the furled growing medium or mesh 130 and the sock 142 holds the spat 136 in place as well as acting as a restraining means. The mesh 130 has provided a far larger surface area when compared to a rope and thus the spat 136 grow in a lower density environment than if socked onto a rope. Water and nutrients may circulate through the centre of the growing line as well as through the mesh spaces.

In Figure 10b, the sock 142 has disintegrated, the spat 136 have matured to larger size and are of relatively even sizes. Furthermore, slide off effect is reduced because of the increased surface area, as more spat 136 are able to attach to the mesh 130 rather than having to rely upon a single foothold mussel carrying a large number of other spat.

Therefore, socking spat 'outside' the furl provides for even growth and increased yield.

Referring now to Figure 4, slide off effect is also reduced because the spat 136 may attach to each other (a stronger bond than to artificial growing lines) through the mesh spaces. Byssal threads 137 extend through the mesh 130 to attach to spat 136 located on the other side of the mesh. As the bond to another mussel is less likely to fail than a bond to an artificial growing line, this arrangement results in higher yield - spat are interlocked with the mesh 130.

In Figure 11a, the socked spat 136 have been loaded onto the 'inside' of the furled growing medium or mesh 130 and the sock 142 primarily acts as a restraining means, depending on the size of the spat and size of the mesh spaces of mesh 130. Again, the mesh 130 has provided a far larger surface area when compared to a rope and thus the spat 136 grow in a lower density environment than if socked onto a rope. Water and nutrients may circulate through the mesh spaces. In this arrangement, a dense spat column with good strength is formed 'inside' the furl.

In Figure 11 b, the sock 142 has disintegrated, the spat 136 have matured to larger size although not necessarily of even sizes. Some of the spat have migrated to 'outside' positions, but many remain 'inside'. The spat 136 in the dense spat column trapped inside the furled mesh 130 therefore will not suffer from slide off effect. Slide off effect on 'outside' spat is also reduced because of the increased surface area, as more spat 136 are able to attach to the mesh 130 rather than having to rely upon a single foothold mussel carrying a large number of other spat. Referring again to Figure 4, slide off effect is also reduced because the spat 136 may attach to each other (a stronger bond than to artificial growing lines) through the mesh spaces. Byssal threads 137 extend through the mesh 130 to attach to spat 136 located on the other side of the mesh. As the bond to another mussel is less likely to fail than a bond to an artificial growing line, this arrangement results in higher yield - spat are interlocked with the mesh 130.

Therefore, socking spat 'inside' the furl provides for increased yield. Advantages and alternatives

Where a decomposable knitted sock has been used when spat are socked onto a growing medium and put back into the water, it is useful to still provide alternative restraining means such as non-decomposable rings, or even aquaculture support devices. These non-decomposable restraining means may also serve as weights for the growing lines. The reason it is useful to restrain the growing mesh in a furled position is that unfurling of the mesh nets will cause interference with adjacent growing lines placed upon a long line (e.g. a horizontal support line.) This then limits the number of collection mediums that may be placed on that long line as entanglement or damage can be caused to neighbouring growing lines by the unfurling of an adjacent growing line. It is also useful to use restraining means such as a sock to adjust the degree of furling of the growing mesh.

Alternative embodiments of the invention may include a central rope for additional strength, surrounded by furled square mesh collection and growing medium according to an embodiment of the invention, surrounded by restraining means being a diamond mesh. The diamond mesh acts as restraining means to hold the collection and growing medium in the furled position, such that it provides the correct spacing to obtain optimal (low) density of spat collection and prevents entanglement with adjacent growing lines.

The overall structure provides an elongate line with good strength, appropriate area for optimal (low) density spat collection and for good circulation of water and nutrients to the spat. While some spat may collect on the rope, they are unlikely to clump as better positions on the collection and growing medium are available with better nutrient availability. Use of a rope is optional - while it does provide additional weight bearing strength, it also requires additional handling and storage volume on a boat.

Further variations having additional mesh layers (or other restraining means) are also envisaged.

The preferred embodiments of the present invention address the issue of the size range typical of collected wild mussel spat. Use of the invention provides a more uniformly sized and economically produced mussel for commercial sale, as well as reducing the labour involved in obtaining and promoting healthy mussel growth.

The spat collection and growing medium according to the present invention is advantageously used both for initial spat collection and growth, and as a substitute for a rope-type line after the density adjustment socking operation. Similar to the post larval spat collected on a collection medium, the density adjusted spat will also benefit from the increased water and nutrient flow provided by the growing medium, resulting in even growth through to harvest, or will benefit from the increased yield obtained through very low losses from slide off effect.

Use of the present invention has advantages in that socked spat may be distributed upon a larger effective surface area and hence at a lower density when compared with using a rope as the growing medium. Improved water and nutrient circulation is obtained, as water and nutrients circulate through mesh spaces and inside mesh tubes/furls, as well as outside the tube/furl. As spat grow and increase in weight, the growing mesh according to the present invention resists collapse. A given mesh can be restrained or furled to the degree required to obtain optimal spat density. For example, a mesh having large mesh spaces may be restrained or more tightly furled than a mesh with small mesh spaces, such that the two meshes will result in similar density of spat. The ability to adjust the mesh in order to obtain a particular spat density is useful where spat has been graded for size, and each growing line has a different size of spat socked upon it.

Claims

CLAIMS:

1. A mollusc spat collection and growing medium including a collection and growing mesh having a longitudinal axis, said mesh having a plurality of transversely spaced longitudinal strands extending parallel to said adjacent longitudinal axis and having spacing means for spacing adjacent longitudinal strands, wherein the transverse spacing of said adjacent longitudinal strands is substantially unaffected by application of a longitudinal load, whereby in use any spat collected or growing upon the medium remain transversely spaced as said spat grow, thereby optimizing growing conditions.

2. A mollusc spat collection and growing medium according to claim 1 wherein said spacing means includes a plurality of longitudinally spaced transversely extending strands intersecting said longitudinal strands, to form a plurality of mesh spaces.

3. A mollusc spat collection and growing medium according to claim 2 wherein said transversely extending strands are stiff and are permanently fixed to said longitudinal strands at each intersection between said transverse strands and said longitudinal strands.

4. A mollusc spat collection and growing medium according to any one of the preceding claims 2 to 3 wherein each of said plurality of mesh spaces is rectangular or each of said plurality of mesh spaces is square.

5. A mollusc spat collection and growing medium according to any one of the preceding claims wherein the strands are plastic or polypropylene.

6. A mollusc spat collection and growing medium according to any one of the preceding claims wherein the collection and growing mesh is a tube.

7. A mollusc spat collection and growing medium according to any one of the preceding claims wherein the strands are a thread ply, tubular or a ribbon.

8. A mollusc spat collection and growing medium according to any one of the preceding claims wherein the longitudinal strands remain substantially of constant length when longitudinally loaded.

9. A mollusc spat collection and growing medium according to any one of the preceding claims wherein said growing mesh is resilient.

10. A mollusc spat collection and growing medium according to any one of the preceding claims further including a longitudinal rope.

11. A mollusc spat collection and growing medium according to any one of the preceding claims further including restraining means for restraining said growing mesh in a furled position.

12. A mollusc spat collection and growing medium according to claim 11 wherein said restraining means is a ring or an aquaculture support device.

13. A mollusc spat collection and growing medium according to claim 11 wherein said restraining means is a sock for substantially enclosing said growing mesh in the furled position, said sock being a knitted sock or having a plurality of diamond shaped mesh spaces.

14. A mollusc spat collection and growing medium according to any one of the preceding claims wherein the collection and growing mesh is provided as a continuous length on a roll.

15. A mollusc spat collection and growing medium according any one of the preceding claims wherein each said of mesh spaces is a square of between 5 to 50mm x 5 to 50mm, preferably of between 10mm to 30mm x 10mm to 30mm, more preferably of 25mm x 25mm.

16. Use of a mollusc spat collection and growing medium according to any one of the preceding claims in the collection or growing of molluscs.

17. Use of a mollusc spat collection and growing medium according to any one of the preceding claims in a method of farming molluscs, the method including the step of socking spat either internally or externally of said growing mesh.

18. A mollusc farming method including the steps of: providing a spat collection and growing medium according to any one of the preceding claims; allowing spat to collect upon said medium and grow into juvenile molluscs; adjusting the density of said juvenile molluscs; and allowing the adjusted juvenile molluscs to grow to maturity.

19. A mollusc farming method according to claim 18 including the further steps of: stripping the juvenile molluscs from said medium; and performing density adjustment by socking the stripped juvenile molluscs.

20. A mollusc farming method according to claim 19 wherein the spat are socked on said collection and growing medium, or on a second collection and growing medium.

21. A mollusc spat collection and growing medium substantially as hereinbefore described, with reference to any one of the embodiments shown in the accompanying Figures 1 , 4, 5a, 5d, 6a to 12, 14a to 14b.

22. Use of a mollusc spat collection and growing medium substantially as hereinbefore described, with reference to any one of the embodiments shown in the accompanying Figures 1 , 4, 5a, 5d, 6a to 12, 14a to 14b.

23. A mollusc farming method substantially as hereinbefore described, with reference to any one of the embodiments shown in the accompanying Figures 1 , 4, 5a, 5d, 6a to 12, 14a to 14b.