GB2575438A - System and method for processing shellfish - Google Patents

Abstract

A method and system for removing tunicates (sea squirts) and other bycatch from a population of cultivated shellfish such as mussels involves providing a liquid flow medium to a bed of shellfish 5 within a vessel 1 via an inlet 16, perturbing or fluidising the bed of shellfish with a source of energy such as the flow of liquid so as to dissociate the tunicates from the shellfish and removing the shellfish and/or the tunicates. Enables efficient removal of saleable shellfish product whilst at the same time allowing immature shellfish to be safely recovered and re-used in cultivation. May be used as part of a de-roping and tubing method. The vessel may be fitted on a boat.

Description

System and Method for Processing Shellfish

FIELD OF THE INVENTION

The present invention relates to cultivation of shellfish such as mussels. More particularly, the invention concerns a method and apparatus for treating shellfish to remove bycatch and detritus such as sea squirts.

BACKGROUND OF THE INVENTION

Farmed or cultivated shellfish, such as mussels are increasingly commonplace. Due to limited available sites for cultivation and due to the long growing period of three to four years, yield is increasingly important.

The process of mussel cultivation typically starts with setting the ropes and collecting wild spats, followed by three years of growth on the ropes which are suspended from floats or rafts in a seawater in a tidal area. After the third year, typically, the mussels are harvested. This involves lifting the ropes, stripping and declumping of the mussels from the ropes. This includes sea squirts and other by-catch that may have populated the ropes or mussel population and any other detritus. The larger mussels are then separated out using a grading machine. The remaining catch of smaller mussels, sea squirts and other by-catch are typically returned to the water or disposed of.

One problem with current methods is that sea squirts take up space on ropes that could be populated by mussels, thus limiting growth of mussels or population of mussels. In addition, it is an established problem for the mussel cultivation industry that sea squirts’ parasitic cohabitation with mussels leads to reduced growth rate due to lack of nutrients and water and occasional loss of mussels from ropes. Thirdly, with the entanglement of sea squirts with byssus, small mussels and other detritus leads to loss of semi-mature mussels during harvest.

WO-A-1998/003753 describes a system for the harvesting of mussels from socked ropes in which the mussels are stripped by pulling the rope through an aperture the diameter of which causes the mussels bound to the rope to

-1 be stripped off. Adjacent tube members are supplied with an upward flow of water which serve to suck the mussels along with foreign matter into adjacent passageways and away for further handling. Whilst there is an up-flow of water treatment, this is for transportation of the mussels themselves and does not concern separation.

GB-A-2444564 describes a method of mussel cultivation on a culturing bed. According to this method, after harvesting of the mussels, they are subject to a washing step to separate mussels from debris and recycling the empty shells and seed mussels by placing them on a further culturing bed for a further cycle of cultivation. The washing step comprise a gentle washing system to allow gradual filtering and washing away of small grit and seed mussel followed by the harvested mussel.

CN 202197679U concerns a mussel harvesting and cleaning machine for mature mussels from shallow sea-floating raft cultivation. It provides a system for removing mussels from its growth structure (e.g. ropes) causing continuous deposition of harvested mussels into a cleaning drum, which is rotatable and fed with a flow of water. The drum has multiple holes of 3cm diameter which cause the debris to be flushed away. This does not concern, particularly, the problem of tunicate and other bycatch and does not utilise upward flowing water.

The present inventor has found a solution to the aforementioned shortcomings in mussel cultivation.

PROBLEM TO BE SOLVED BY THE INVENTION

There is a need for improvements in shellfish aquaculture, in particular mussel cultivation such rope-cultivation of mussels that allow improved yields and improved harvesting processes.

It is an object of the invention to provide an improved method of harvesting shellfish such as mussels, that is more efficient and enables higher yield cultivation;

-2It is a further object of the invention to provide a method and system for separating tunicate, other bycatch and detritus from cultivated shellfish populations.

SUMMARY OF THE INVENTION

In accordance with a first aspect of the invention, there is provided a method of removing tunicates and other bycatch from a population of cultivated shellfish, the method comprising: disposing into a vessel a population of cultivated shellfish to provide a bed of cultivated shellfish, which vessel is configured for separation of tunicates and other bycatch from a bed of shellfish in a liquid medium and which has a liquid medium flow inlet; passing a liquid medium through the bed of shellfish in the vessel via the liquid medium flow inlet; providing a source of energy to the bed of shellfish in the vessel to disturb or move or fluidise the shellfish in the bed of shellfish and dissociate the tunicate and other bycatch therefrom; and removing the shellfish and/or the tunicates and other bycatch from the vessel.

In a second aspect of the invention, there is provided a method for recovering immature shellfish from a harvestable population, the method comprising the steps of the above method of removing tunicates and other bycatch and further comprising removing the immature shellfish for re-cultivation.

In a third aspect of the invention, there is provided a method for thinning and re-tubing mussels in a rope-based mussel cultivation system, the method comprising after one or two years of growth, de-roping and de-clumping the population of cultivated mussels, removing any tunicates or bycatch according to the method above, removing the dissociated mussels, grading the dissociated mussels and re-tubing a grade of dissociated mussels by placing onto a cultivation rope in a tubing step.

In a fourth aspect of the invention, there is provided a system for the removal of tunicates and other bycatch from a population of cultivated shellfish the system comprising: a vessel of a size and configured to receive a population of cultivated shellfish and having a base for forming a bed of cultivated

-3 shellfish on, the vessel having at least one liquid medium flow inlet for providing inflow of a liquid medium to the vessel; and a perturbation energy means for providing to the vessel sufficient energy to disturb or move or fluidise shellfish in a bed of shellfish and dissociate the tunicates and other bycatch therefrom.

In a fifth aspect of the invention, there is provided a vessel for use in a system as defined above, the vessel being of a size and configured to receive a population of cultivated shellfish and having a base for forming a bed of cultivated shellfish on, the vessel having at least one liquid medium flow inlet for providing inflow of a liquid medium to the vessel.

In a sixth aspect of the invention, there is provided a boat fitted with a system or a vessel as defined above.

ADVANTAGES OF THE INVENTION

The system and method and other aspects of the invention provide two key advantages to shellfish cultivation and, especially, mussel cultivation using ropes. Firstly, in the process of harvesting mature shellfish, it enables the efficient removal of saleable product whilst at the same time allowing immature shellfish to be safely recovered and re-used in cultivation, thus improving cultivation intensity and, secondly, it allows effective and efficient thinning of immature cultivated mussel populations ad removal of tunicate and other bycatch to enable more efficient mussel growth and improved yields.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure lisa flowchart illustrating an example of a rope-based mussel cultivation and harvesting process;

Figure 2 is a cross-sectional side view of a vessel according to one embodiment of the invention;

Figure 3 is a cross-sectional end view of the vessel of Figure 2;

Figure 4 is a perspective view of a vessel in cut-away according to another embodiment of the invention; and

-4Figure 5 is cross-sectional side view of a vessel according to another embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

The invention concerns a system and method for removing tunicates, such as sea squirts, and other bycatch and detritus from a population of cultivated shellfish, such as mussels. The shellfish may then be selected for further cultivation if they are immature or further processed for market. The invention in further aspects includes a method of thinning a population of cultivated shellfish and a method of cultivating shellfish incorporating the above methods.

According to the system and method, a vessel is provided, typically an oblong vessel having a base and four sides, which vessel is configured for separation of tunicates and other bycatch from a bed of shellfish in a liquid medium and which has a liquid medium flow inlet.

A population of cultivated shellfish is disposed into the vessel to form a bed of cultivated shellfish.

A liquid medium is passed through the bed of shellfish in the vessel via the liquid medium flow inlet.

A source of energy or perturbation energy means is provided to the bed of shellfish in the vessel to disturb or move or fluidise the shellfish in the bed of shellfish and dissociate the tunicates and other bycatch therefrom.

According to the method of the invention, the cleaned cultivated shellfish or separated tunicates or other bycatch and detritus may then be removed from the vessel.

The system may be installed and the method carried out on land, but it is preferably is carried out on water, such as in a floating factory on a pontoon or similar, but preferably on a boat, typically being used in commercial shellfish cultivation.

Preferably, according to the method of the invention, a liquid medium is provided by way of a carrier fluid through which the shellfish will pass

-5 in the vessel and preferably which will entrain tunicates and other bycatch and detritus to facilitate dissociation and separation from the population of cultivated shellfish.

The source of energy or perturbation energy means may be provided by any suitable means or combination of means that can cause perturbation of mussel bed or more preferably fluidisation. The source of energy or perturbation energy means may provide continuous or intermittent perturbation/fluidisation. More than one sources of energy or perturbation energy means may be used in sequence or in concert. Preferably, the sources of energy or perturbation energy means are controllable to enable varied energy input and thus different degrees of perturbation or fluidisation, and more preferably, this is controllable along a length of the vessel or shellfish flow path. Further, the energy provided may be configured to vary along a width of the vessel or shellfish flow path since the bed of shellfish at the sides of the vessel may be more likely to remain settled.

The source of energy or perturbation energy means may include one or a combination of liquid medium flows (e.g. pressurised liquid medium flows) or liquid medium jets, vibrational energy via vibration means beneath or in the vessel and optionally disposed within the bed of shellfish, one or more pressurised air streams configured within the vessel or to a lower portion of the vessel, actuating baffles configured in or toward a base of the vessel, and mechanical mixing members disposed in the vessel at a lower portion or common with the bed of shellfish.

Where the source of energy or perturbation energy means comprises vibrational energy via vibration means beneath or in the vessel and optionally disposed within the bed of shellfish, this may comprise a suspended or raised base onto which the bed of shellfish may be formed, which raised base may be a vibrational member and/or comprise vibrational members disposed thereon or beneath. The vibrational members should be configured to vibrate at a frequency and amplitude so as to cause perturbation and preferably fluidisation of the shellfish bed (or contribute thereto). Preferably, the degree of vibrational energy is

-6controllable so that the degree of perturbation can be controlled. Optionally, vibrational perturbation means are provided only along portions of a flow path of shellfish through the vessel and/or is controllable as between different fluidisation zones along a length of the vessel or flow path of the shellfish.

Where the source of energy or perturbation energy means comprises one or more pressurised air streams configured within the vessel or to a lower portion of the vessel, the pressurised air streams are configured to be directed into the vessel and through a liquid carrier medium in the vessel. Preferably, the pressurised air streams are provided toward the bottom of the vessel so as to pass through a bed of shellfish formed on a base thereof so as to impart energy to the bed to cause perturbation and preferably fluidisation thereof. More preferably, the pressurised air stream is provided at multiple points at or through the base (e.g. a suspended base) of the vessel. Preferably, the pressurised air is provided via a plurality of diffusion valves in or on the base. Preferably, the pressure of air flow in the air streams is controllable so that the degree of perturbation can be controlled. Optionally, pressurised air streams are provided only along portions of a flow path of shellfish through the vessel and/or is controllable as between different fluidisation zones along a length of the vessel or flow path of shellfish.

Where the source of energy or perturbation energy means comprises mechanical mixing members disposed in the vessel or actuating baffles configured in or toward a base of the vessel, it is preferred that these are provided in a manner to transfer energy to the shellfish bed to facilitate fluidisation, to facilitate dissociation of tunicates therefrom whilst minimizing physical damage to the shellfish. In one embodiment, the mixing members comprise a plurality of actuating elongate baffles disposed on a base of the across a flow path of shellfish which actuate back and fore along the intended flow bath. Alternatively, there are a plurality of multi-finned mixers rotatably mounted on a base of the vessel which physically transfer energy to the shellfish and via the liquid medium. Alternatively, a series of elongate paddle wheel mixer members are disposed along a length of the flow path of shellfish, each extending laterally across the vessel.

-7Optionally, the mixer members may be separated by mesh or cage elements or sunk into a raised base of the vessel so as to impart energy to the bed via a liquid medium rather than by direct mechanical contact thereby reducing the risk of physical damage to the cultivated shellfish.

When pressurised and/or high flow-rate liquid medium flow or liquid medium jets are used as the source of energy or perturbation energy means for causing perturbation and preferably fluidisation of the bed of shellfish, multiple streams of liquid medium are provided into the vessel so as to project into the bed of shellfish, in a lower portion of the vessel, via the sides of vessel and/or (and more preferably) via a base on which a bed of shellfish may form so as to project into the bed of shellfish from below. The multiple streams or flows of liquid medium into the vessel are preferably at sufficient flow rate or flow velocity to cause fluidisation of a bed of shellfish formed on the base of the vessel. Preferably, the pressure and/or flow rate of liquid medium is controllable so that the degree of perturbation can be controlled. Optionally, the pressure and/or flow rate of the liquid medium is controllable as between different fluidisation zones along a length of the vessel or flow path of shellfish and/or through different apertures leading to the shellfish bed, so that different degrees of fluidisation may be provided at different parts of the process.

Preferably, the source of energy or perturbation energy means comprises a liquid medium flow into the bed of shellfish.

In the method of the invention, a liquid medium is passed through the bed of shellfish in the vessel via a liquid medium flow inlet thereby acting as a carrier fluid for the system. Preferably, where the source of energy or perturbation energy means is a flow (or multiple flows) of liquid medium, the source of energy or perturbation energy means provides the passing of liquid medium through the bed of shellfish and vice versa.

The liquid medium providing a carrier fluid and effecting the fluidisation is preferably pumped into the vessel by means of one or more liquid medium inlets (typically through in a lower portion of the vessel) via one or more liquid medium pumps.

-8Preferably, the liquid medium is water and may be sea-water. The sea-water may be provided to the vessel via a pipe or conduit drawing water from the sea.

Alternatively, the liquid medium, which may typically be seawater, may be recycled through the system and a holding tank provided for collecting water as it leaves the vessel and from which a pipe for drawing water (e.g. via a pump) may lead to an inlet to the vessel.

Optionally, the liquid medium, according to some embodiments, may be treated water, especially when applying the method and system at the point of harvest in order to remove tunicates and other bycatch from harvestable shellfish, such as mussels. The treated water may be treated, e.g. by UV treatment, and may be used for example for depuration of the shellfish, such as for removal of or reducing the concentration of microbiological contaminants, chemical contaminants or other natural toxins. According to this embodiment, the treated water may be UV treated water. The residence time for the purpose of depuration may be reduced compared with conventional depuration methodologies due to the perturbation and fluidization. Optionally residence time for this purpose (depuration) may be up to 6 hours, preferably up to 3 hours. Typically, it is at least 20 minutes, more preferably at least 1 hour.

The system and method of the present invention may be configured for either batch or continuous operation. For batch operation, there may be a static fluidised bed of cultivated shellfish from which tunicate and other bycatch and detritus may be dissociated by way of fluidisation preferably entrained in a through-flowing liquid medium to an outlet thereby separating the tunicate from the shellfish. The cleaned shellfish of the batch may then be removed from the vessel. Alternatively, for batch operation, the population of shellfish in a fluidised bed moves along a flow path from one end of the vessel to another. For continuous operation, there is preferably a fluidised bed to facilitate movement of a population of cultivated shellfish from one end of the vessel to another, typically driven by addition of further shellfish in an inlet and with an optional outlet arrangement at the other end.

-9Preferably, the method and system is for continuous processing (or continuous batch processing).

The method and system of the invention preferably allows a passage of a population of cultivated shellfish through the vessel from a shellfish population inlet, to a base where a bed of cultivated shellfish is formed and optionally to a shellfish outlet. Notwithstanding the actual dimensions or shape of a vessel, the relative directions of longitudinal and lateral should be generally considered as respectively referring to being general common with the flow path of cultivated shellfish and lateral to the flow path of cultivated shellfish.

The shellfish flow path referred to comprises the passage of shellfish through the system during operation and typically from a shellfish population inlet, which may be fed by a hopper, especially for continuous operation to a shellfish outlet (being typically the ‘downstream’ end of a shellfish fluidised bed). The shellfish in a fluidised bed on a base tend to progress toward an opposing end to the inlet (e.g. in a linear vessel) or the other end from the inlet (in any shaped vessel) driven by the further addition of shellfish through the inlet. Optionally, the vessel may be configured to define a shellfish flow path that is not linear (e g. may curve or bend) to allow a longer flow path in a given area. In this case, the longitudinal direction is typically considered the shellfish flow path direction at any given position. The flow path may pass multiple fluidisation zones by which it is meant zones with different fluidisation properties (or zones capable of having different fluidisation properties).

Preferably, the cleaned shellfish progress through a shellfish outlet.

The system and method of the invention are preferably configured to enable a pre-defined residence time to allow at least a significant proportion of tunicates (and/or other bycatch) to be removed or dissociated from the shellfish. The residence time of the system and method may be selected according to the desired throughput of shellfish in the system, the degree of perturbation, the desired proportion of tunicate removal and the size of the system (and correspondingly the size, e.g. volume and length, of the system may be selected accordingly). Preferably, the residence time may be at least 30 seconds, and

- 10 more usually at least 1 minute and may be up to 1 hour or more (e.g. up to 6 hours, especially where depuration is used). More preferably, the residence time is selected to be up to about 40 minutes, more preferably up to about 30 minutes and still more preferably up to about 20 minutes. In one embodiment, the residence time may be from 2 to 3 minutes and in another embodiment from 5 to 10 minutes. In a particularly preferred embodiment, the residence time is selected to remove at least 80% of the (weight) of tunicates (especially sea squirts) in the range 3 to 10 minutes.

As mentioned above, the liquid medium is preferably water (e.g. sea water) and hereinafter water will be referred to (although where the context allows, it is considered that other liquid mediums may be contemplated in the following discussion).

The water flow through the vessel preferably comprises one or multiple inlets provided in a lower portion of the vessel and preferably configured to flow through a bed of shellfish from below, e.g. through a base (e.g. a raised base) of the vessel. Preferably, there are multiple water flow inlet apertures formed in a base through which water, preferably pressurised water, may flow. The water will be retained within the vessel as it flows into the vessel until an equilibrium level is reached. An equilibrium level is reached when water flowing into the vessel is the same quantity as water flowing out of the vessel. Preferably, one or a plurality of water outlets are provided in the vessel, preferably at an upper portion thereof. Preferably, the water outlets are configured as overflow weirs over which water may flow when it approaches and reaches the equilibrium level. The overflow outlet weirs may be formed in any or all sides of the vessel, but preferably in one side (rather than one end) of the vessel. There may be one overflow outlet weirs or multiple overflow outlet weirs. Thus, the flow path of water is preferably generally upward from an inlet in a lower portion, preferably through the base (e g. a raised base) of the vessel and out through an overflow outlet weir. The liquid flow outlets are preferably configured (e.g. number of liquid flow outlets and size, e.g. width, of liquid flow outlets) for a particular flow rate of water to have sufficient depth of water flowing over the weir to carry the

- 11 tunicates (e.g. sea squirts) out of the vessel. Similarly, the liquid flow outlets have to be of sufficient size to cope with the quantity of liquid passing through the system. Typically, the weir’s may occupy, cumulatively, up to 50% of the perimeter of a vessel e.g. from 20 to 40% or from 50 to 75% of the length of a side of a vessel. In any case, it is preferred for a particular system that the free water surface (that is the equilibrium level during use) above the water exit weir during operation is at least 15 mm, more preferably at least 20 mm, e.g. from 20 to 30 mm.

The flow rate of water is preferably sufficient to entrain relatively low density (relative to the cultivated shellfish population) tunicate or other bycatch into the water flow and to an upper portion of the tank and optionally removed manually, or by a removal mechanism or to exit via the overflow outlet weir with the water flow. Preferably, the flow rate of the water flow is controllable to ensure an appropriate flow rate for removal of dissociated tunicate or bycatch. By varying the flow rate, the nature of the entrained bycatch or other items (e.g. spats or immature shellfish) may be controllably and selectively removed from the process. In particular, it is preferable that the flow rate can be varied along the length of the vessel (i.e. along a flow path of shellfish).

By spat, as used herein, it is meant a very young shellfish after settlement or attachment. In the case of mussels, spat may further, preferably, be defined as having a length of up to 20 mm. By immature shellfish, it is meant a young shellfish that is considered below marketable size, preferably in the case of mussels having been cultivated or settled for 18 months or less and/or having a length of 100 mm or less. Mature shellfish may be considered those of marketable size and further, in the case of mussels, may be defined as having been cultivated or settled for more than 18 months, e.g. more than 2 years, and have a length of greater than 100 mm, e.g. 110 mm or more, such as 150 mm or more.

In a preferred embodiment, in which the liquid medium is water and the source of energy comprises the passage of water flows into the vessel, the flow rate may be established according to the depth of bed at various points along the shellfish flow path to cause a degree of perturbation and preferably fluidization

- 12 at one or more positions along the shellfish flow path, and preferably all along the shellfish flow path. Thus, the flow rate of water through the bed is preferably selected to enable perturbation and preferably fluidisation and also to entrain tunicates and other bycatch into the water flow and thereby enable removal of tunicates In any case, it is preferable that a range of different or variable pressures or flow rates of water flow may be defined along the flow path of the shellfish bed (e.g. between different or successive fluidisation zones or sections).

In one embodiment, the flow rate of water through apertures in a base and thus through the bed may preferably be, especially for mussel fluidisation, at least 0.005 m/s, more preferably at least 0.01 m/s and still more preferably at least 0.02 m/s. Flow rates of up to 0.1 m/s may be suitable, but preferably are in the range from 0.02 to 0.05 m/s. Volumetric flow rate may be dependent upon the size of the vessel, but is preferably, for a typical system, at least 5 litres per second and up to 100 litres per second, e.g. up to 50 litres per second, more preferably from 7 to 20 litres, per second, e.g. up to 15 litres per second and preferably about 10 litres per second. This is particularly the case for preferred dimensions of vessel as are discussed below.

The vessel preferably comprises a raised base onto which the cultivated shellfish may be disposed and form a bed of shellfish. The raised base preferably comprises a plurality or array of apertures through which water may be fed by one or more reservoirs or which may be fed by a plurality of conduits or pipes (for each or a smaller array of apertures). In one embodiment, the raised base comprises a solid sheet with a plurality of apertures formed therein (e.g. stamped out) to define an array of apertures. The apertures may be consistently sized and spaced or may vary in size or space, e.g. larger or closer together closer to the sides, or larger or closer together in different fluidisation zones of the flow path. In a second embodiment, the raised base comprises a wire mesh providing an array of apertures, which wire may be of varied thickness in different parts of the base or may be consistent and wherein the mesh size may be consistent or vary at different parts of the base.

- 13 In one embodiment, the raised base defines a space beneath which may be occupied by pipework leading to a plurality of water flow apertures in the base or may define a reservoir or a plurality of discrete reservoirs feeding the plurality of water flow apertures in the base. Where one or more reservoirs are provided, water may be fed into the or each reservoir from an external water source (e.g. sea water from the sea, over the side of a boat on which the system is formed) via a pipe and via a pump for pumping the water through a water inlet in a lower portion of the reservoir. At least one water inlet may be provided into the or each reservoir. The water is typically pumped at high pressure or high flow rate (e.g. through a suitably large aperture inlet if feeding into one or more reservoirs) so that water may be forced out of the reservoir(s) via the apertures in the base and into the main body of the vessel at sufficient pressure to cause perturbation and preferably fluidisation of the bed of shellfish thereon.

The inlet apertures may be sized to provide a pre-defined pressure at a certain flow rate and preferably are sufficiently small that shellfish from the shellfish bed, even immature shellfish, may not pass. Optionally, apertures may be provided with a mesh to prevent ingress of detritus and spats.

The inlet apertures in the base may be for example up to 2 cm across and preferably at least 2 mm, more preferably up to 1.5 cm, more preferably in the range 5 to 10 mm across (e.g. in diameter in the case of circular apertures).

The vessel preferably comprises a main chamber and a second chamber or discharge tank. The main chamber is preferably the chamber in which a fluidised bed of shellfish may be provided and through which water flows upward from a (preferably raised) base and out over overflow outlet weirs formed at an upper edge or side of the vessel. The flow path of shellfish preferably passes through the main chamber to a shellfish outlet which leads to a second chamber at which point tunicate is preferably dissociated from the shellfish and separated from the shellfish bed (and ideally removed from the vessel). The cleaned shellfish may pass through into the second chamber from which it may be removed, manually or via a solid transfer mechanism.

- 14 The shellfish outlet preferably is defined by an outlet weir. The outlet weir preferably is raised relative to the base of the main chamber. The outlet weir and the base may be moveable relative to one another (e.g. one or both of the weir and base may be adjustable in height) thereby varying the size of shellfish that are allowed to pass into the second chamber. Typically, smaller shellfish occupy an upper portion of the fluidised bed while larger shellfish may occupy the lower portion. The control of water flow rate/pressure may also facilitate control of size of shellfish that may pass into the second chamber. These features together may be considered a form of grading mechanism.

The shellfish outlet is preferably further defined by a lateral vane extending from above an equilibrium water level (to prevent flow of water and tunicates over the vane and into the second chamber) and extending into the vessel, dividing the first chamber and second chamber) toward the weir and defining an outlet aperture therewith.

The vessel and in particular the main chamber may according to a preferred embodiment comprise one or more baffles, e.g. laterally disposed, preferably in a lower to mid portion of the vessel on or above the base to facilitate mixing and movement of the shellfish in the fluidised bed and/or to increase residence time of shellfish in the fluidised bed. Optionally, the baffles are movable and/or may be vibrated (e.g. to provide further fluidisation energy). Optionally a series of transverse baffles (extending laterally across the flow path) and extending upward from the base may be provided to effectively increase the flow path and thus the residence time as well as to cause further perturbation and contact to facilitate removal of tunicates. For example, there may be provided two to ten baffles along the flow path of the vessel, such as from 3 to 8, or 4 to 6.

The vessel and, in particular, the main chamber may according to a preferred embodiment comprise one or more vanes preferably disposed in an upper portion of the main chamber of the vessel typically extending from above the equilibrium level of water (e.g. above the water overflow outlet weir position) into the body of the vessel, e.g. to a mid-depth within the vessel. These may be configured to inhibit passage of relatively low density materials, such as

- 15 dissociated tunicate along the length of the vessel and may optionally be disposed at an angle to direct such materials and water toward an overflow outlet weir (or to an alternative tunicate removal arrangement).

Optionally a series of transverse vanes (extending laterally across the flow path) and extending downward from a freeboard area into the bed of shellfish may be provided to effectively increase the flow path and thus the residence time as well as to cause further perturbation and contact to facilitate removal of tunicates. For example, there may be provided two to ten vanes along the flow path of the vessel, such as from 3 to 8, or 4 to 6.

In one embodiment, especially for use with oysters or scallops, there may be provided a plurality of rods or similar protrusions disposed in the freeboard portion of the vessel above the shellfish bed, which rods extend downward toward the bed. The rods may be spaced at distances of slightly less than the width of a marketable or mature oyster or scallop, e.g. from 5 to 20 cm separation (e.g. 8 to 12 cm), depending upon the species. The function of such rods is that where a scallop or oyster may become entrained in the water flow and flow upward toward the water outlet, it may be ‘tipped’ by collision with the rod from a generally flat or horizontal orientation to an upright (or end up) orientation, whereby it may fall out of entrainment by the water flow and return to the bed. By this means, loss of shellfish through the water outflow may be avoided.

The second chamber is typically not subject to a fluidising or perturbation energy and cleaned shellfish may settle in the second chamber. They may be removed manually or automatically. Optionally a solid transfer mechanism is provided to remove the shellfish from the second chamber, such as a paddled conveyor or Archimedean screw mechanism.

In one preferred embodiment, the vessel and, in particular, a main chamber, comprises multiple fluidisation zones or sections. Each fluidisation zone preferably comprises water flow inlets in a base (preferably raised) that are independently controllable in terms of flow rate and/or flow pressure (and where other perturbation energy means are provided, these may be independently controllable as between the fluidisation zones) whereby different degrees of

- 16 fluidisation of the bed of shellfish may be provided in each of the fluidisation zones. Associated with each fluidisation zone is preferably a water flow inlet arrangement, which preferably comprises a discrete reservoir beneath the base feeding an array of water flow apertures in the base and being served by at least one dedicated water inlet and dedicated pumping means. Thus, each reservoir may be independently controlled in terms of the pressure and flow rate of water into it and thus the pressure and flow rate of water into the respective fluidisation zone. This may allow selective dissociation of certain materials, such as tunicates, other bycatch and detritus from the shellfish bed according to, say, the pressure of water passing through the shellfish bed and may allow selective entrainment of certain materials into the water flow and separate from the bed of shellfish according to the relative density of that material, such as tunicate or category of tunicate, other bycatch, detritus such as loose byssus, and optionally immature shellfish or spats. Thus, such materials may be selectively entrained in different fluidisation zones of the system.

Preferably, associated with each fluidisation zone is an arrangement of vanes extending across the main body of the vessel protruding to above the typical equilibrium water level (and above an upstream overflow outlet weir level). The vane extends into the body of the main chamber to a mid-depth (e.g. extending through a freeboard section but not into or not substantially into a shellfish bed), serving to essentially separate an upper portion (or freeboard section) of one fluidisation zone from another, to inhibit the digression of entrained tunicate or other material from the water flow of one fluidisation zone to another. As such, there is preferably also provided water outlets, typically overflow outlet weirs but optionally other arrangements, for each fluidisation zone leading to the same place or to different locations for further treatment or disposal.

Thus, optionally according to the relative energy of fluidisation and water flow rate entrainment energy, tunicates and other bycatch, detritus and immature shellfish may be selectively dissociated and removed in successive fluidisation zones of the system and method leaving relatively mature shellfish to be passed, optionally by size selection into a second chamber and optional further

- 17 grading in a solid transfer mechanism out of the second chamber. Thus, spats and immature shellfish can be selectively removed from a population of cultivated shellfish and re-used in a re-cultivated system thus reducing the time to harvest and increasing the yield of a cultivation site.

The vessel, system and method are preferably configured to provide that the bed (i.e. a bed portion of the vessel) may take up from 30 to 70%, preferably 40 to 60% and more preferably about 50% of the height from base (e.g. raised base) to equilibrium level or water outlet level (e.g. weir level), the remainder being defined as a freeboard portion of the depth (or height) of the vessel. Where there is, typically, a raised base, this is preferably 0.2 to 0.4 x the height of the vessel as a whole, more preferably 0.25 to 0.35 x, e.g. about 30% of the height.

A bed portion of the vessel, and thus the bed of shellfish, may be configured according to one embodiment of the system and method to taper outwards from the base (e.g. raised base) upwards. That is, the width of the bed (across the flow path) at base level may be less than the width of the bed at the top of the bed. It may taper at a constant or a variable angle, preferably constant. By this arrangement, flow rate at the bottom of the bed may be controlled to be greater than higher in the bed thus enabling a fluidizing flow rate throughout the bed. The tapered bed may be achieved by, for example, a vessel being shaped to taper out from base upward or, by way of an alternative example, by angled inserts that may be disposed inside the vessel, at the side walls to define a slope from the base to the side wall. By this second means, different taper angles may be achieved by providing different angled inserts.

The vessel, which is preferably provided on a boat, typically a commercial shellfish cultivation boat, may be of any suitable size according to the size of boat and the quantity of shellfish to be processed.

In one embodiment, the vessel (and preferably the main chamber) has a length of at least 0.8 m, e.g. from about 0.8 m to about 5 m, but is preferably from about 1 m to 3 m in length (i.e. from inlet to outlet), e.g. up to 2 m and preferably about 1.5 m long. Preferably, it has a width of at least 0.25 m, more

- 18 preferably 0.3 m e.g. up to 3 m, more preferably up to 2 m, and still more preferably up to 1.5 m. Preferably the width is up to 1 m, e.g. from 400 to 800 cm, such as about 500 cm. The depth of the main chamber may be at least 0.5 m, more preferably at least 0.75 m and may be e.g. up to 1.5 m, more preferably up to

l. 25m, e.g. about 1 m. Where a second chamber is provided, it may be for example from about 0.3 m or from 0.5 m up to about 1 m, such as up to about 0.75

m.

In a preferred embodiment, the vessel has a depth of about 1 m, of which about 30 cm is the reservoir beneath a raised base, about 30 cm is for the shellfish bed and about 30 cm is freeboard with about 10 cm from weir level to the rim of the vessel.

Optionally the vessel has a top cover.

The system according to a preferred embodiment, comprises a control unit for controlling the flow of water and any perturbation energy means, including specific controls for optional fluidization zones within the vessel. The control unit may also control input of shellfish via a hopper and removal via a solid transport mechanism.

The system and method may be used for any type of cultivated shellfish, preferably molluscs, such as mussels, oysters, clams, cockles, pipis or scallops as well as whelks, periwinkles, abalones and conches. It finds particular utility in relation to cultivated mussels, particularly rope or line cultivated mussels.

The tunicate and bycatch to be removed is commonly sea squirt or Ascidiacea. Other bycatch may include microalgae and macroalgae.

Thus, in a preferred embodiment, the methods and systems of embodiments of the present invention may be used in a method of thinning a cultivated population of mussels and a method of cultivating mussels.

According to a method of thinning a cultivated population of mussels, a cultivated mussel population having been in a cultivation system for one to two years’ growth is raised, stripped from a rope, de-clumped and provided to a vessel as defined above and subjected to a method of removing tunicates. In the course of the method, the cleaned mussels are recovered and re-tubed with a

-19 permanent or biodegradable mesh onto a rope and re-set in cultivation for further growth.

In another embodiment, the system and method may be directed to ensuring biosecurity whereby collected specimens (e.g. spat or immature/juvenile shellfish) from one area of water (e.g. one area of seabed) may be subject to the method to remove local co-habiting species (e.g. tunicates and other bycatch) from the collected population at the location of collection prior to transport.

The invention will now be described in more detail, without limitation, with reference to the accompanying Figures.

In Figure 1, an example of a cultivation process in which the methods of the present invention may be adopted is illustrated. The central process in Figure 1 is the cultivation process, which is carried out at sea. This illustrates the setting of ropes and spat collection as the first two steps. Spat collection on set ropes takes place in a suitably tidal location and involves simply leaving the ropes to collect spats in the tide. Once populated, the cultivation requires around three years’ growth. Optionally, there is a thinning step, shown in the ‘Thinning box’ to the left in Figure 1. This comprises stripping cultivated mussels from the rope and declumping. Currently, these are then graded to capture mussels of the appropriate size for re-tubing and placing back in the same or a different cultivation location. Any bycatch and any less mature mussels or spats that do not make the grade are typically disposed of. According to embodiments of the present invention, after stripping and declumping and prior to grading, there may be further a step of removing tunicate and bycatch from the mussels comprising the method described hereinbefore. By carrying out this step, smaller mussels and spats may be recovered before or during the grading process as well as mussels of a suitable size of beginning the second year of cultivation. Further, the process for thinning is much more efficient. In another embodiment, after stripping and declumping during the harvesting process, there may be a further step of removing tunicate and bycatch from the mussels comprising the method described hereinbefore, again before grading. Again, this has the

-20 advantage that as well as enabling grading of saleable mussels, immature mussels may be separated from the tunicate and other bycatch and fed back into the cultivation system by re-tubing and re-setting on ropes, e.g. for a further one or two years cultivation.

After harvesting, the mussels that make the grade for market are transported to a factory where they are washed (optionally) and graded and then processed and packaged for sale.

The thinning and harvesting exercises are typically on boat activities.

In either case, the method of removing tunicate, such as sea squirts, and other bycatch from the population of mussels involves providing a vessel for the purpose which has a base for forming a bed of mussels on (ideally a raised or suspended base), disposing the population of mussels into the vessel, ideally in a continuous process, such as by way of a hopper at one end of the vessel. Sea water is pumped into the vessel, ideally from below the bed via inlets in the raised base. This causes perturbation and movement of the mussels in the bed and should preferably lead to fluidisation, whereby the mussels are in constant state of perturbation or movement. The pressure of the water combined with the movement of mussels against one another cause dissociation of the sea squirts and other bycatch as well as detritus such as byssus. These materials are less dense than the mussel population and become entrained in the water flow within the vessel so becoming physically separated from the mussel population. The sea squirts and other bycatch and detritus may then be removed from the vessel via a water outlet or overflow weir and disposed of. Vanes may be provided to guide them. The mussels in the fluidised bed are continually caused to move toward as second end of the vessel where they pass a weir or similar barrier to a second chamber or discharge tank. The movement toward the second end is caused by continuous addition of harvested mussels into the vessel at the first end. Here, cleaned mussels may be collected. Optionally, a solid transfer system, such as an Archimedes screw arrangement transports the cleaned mussels out of the vessel. This may also act as a grading mechanism.

-21 Specific embodiments of a vessel used in this method are illustrated in Figures 2 to 5.

In Figure 2 and 3, there are shown respectively cross-sectional side and end views of a vessel 1 in operation. The vessel 1 has a raised or suspended base 3 onto which a bed of mussels 5 forms from an introduction of a population of mussels 7 through a mussel population inlet 9, e.g. continuously via a hopper (not shown). Inlet baffle 10 ensures that the population of mussels is controlled to enter at one end of the vessel and push the bed of mussels 5 along. The bed of mussels 5 is fluidised by flow of water at a pre-defined pressure or flow rate into the bed of mussels 5 from below through an array of apertures 11 formed in the raised base 3. A high pressure and/or high flow rate of water caused to pass through the apertures 11 from a reservoir 13 between the raised base 3 and the vessel base 15. This reservoir 13 is fed via water inlet 16 from a pipe (not shown) drawing sea-water from over the side of the boat (not shown) or from a water tank (not shown) via a pump (not shown). The reservoir 13 is therefore during operation a reservoir providing continuous flows of sea water through apertures 11 into the bed of mussels 5 to cause perturbation and preferably fluidisation. The pump is preferably a variable speed pump so that the flow rate and pressure of fluid into the reservoir 13 and thus through the bed of mussels 5 can be controlled.

The water flowing into the vessel 1 flows generally upwards through the apertures 11 through the bed of mussels 5 causing perturbation and fluidisation of the bed of mussels 5 and dissociation of sea squirts and other bycatch and detritus, which due to the relatively low density thereof becomes entrained in the water flow and exits the vessel with the water outflow 19 via an overflow weir 17 once the water has reached an equilibrium level 21 within the vessel 1.

The fluidised bed of mussels 5 moves along the base 3 within a main chamber 23 to a mussel outlet 25 allowing clean mussels 27 to flow into a second chamber or discharge tank 29. Clean mussels 27 settle in this tank 29. They may then be removed manually or via a solid transport system, such as an Archimedes screw arrangement.

-22 The flow of clean mussels 27 into the second chamber 29 via mussel outlet 25 may be controlled via movable outlet weir 31. This may be raised and lowered to allow smaller mussels out (when the weir is raised, since smaller mussels tend to occupy the upper portions of the fluidised mussel bed 5) or to allow larger mussels out (when the weir is lowered). Outlet vane or baffle 33 extending from an upper portion of the vessel 1 down into the water prevents lower density sea squirts and other bycatch from entering the second chamber 29.

Figure 4 illustrates another embodiment of the vessel 1 (the second chamber not illustrated here). In Figure 4, which is illustrated prior to the water level reaching its equilibrium level, the general flow direction of water is shown by the thin arrows, whilst the general flow direction of mussels is shown by the thick arrows. The population of mussels may enter the vessel 1 via mussel inlet 9 controlled by inlet baffle 10. The mussels form a bed 5 on the raised base 3 and are fluidised by a flow of water through apertures in the raised base 3. The mussels move along a length of the vessel 1, the passage controlled by flow control baffle 35, and then through mussel outlet 25 between outlet weir 31 and outlet vane 33 to deposit clean mussels in a second chamber. As the water level rises to its equilibrium, the water will exit the vessel via overflow weir 17 bringing entrained relatively low density material, including sea squirts and dissociated byssus, with it and thus separating this material from the clean mussel population. In this embodiment, water is pumped through water inlets 16 into reservoir 13 from a sea-water source via a pump (not shown).

In Figure 5, a side cross-sectional view of a further embodiment shows an extended vessel 1 having a main chamber 23 with multiple fluidisation compartments or sections 37. Each fluidisation compartment 37 is characterized by a discrete reservoir compartment 39 (each separated by a reservoir partition 40) and a water flow outlet portion 41. As with other embodiments, the vessel 1, comprises a mussel population inlet 9 controlled by inlet baffle 10 to allow a population of mussels to flow into the vessel and form a mussel bed 5 on a raised base 3. Downstream thereof, the fluidised mussels pass flow control baffle 35 and cleaned mussels 27 flow out through mussel outlet 25, between adjustable outlet

-23 weir 31 and outlet vane 33 into second chamber 29. Fluidisation of the mussel bed 5 is provided by water flow through apertures 11 from each of three discreet reservoir compartments 39. Each reservoir compartment 39 is fed by dedicated water inlet 16 providing seawater via pumps that are individually controllable allowing different water pressures to be present in each discrete reservoir compartment 39 and thus different water pressure to flow through apertures 11 in each fluidisation section 37. Thus, the degree of perturbation of fluidisation along the length of the mussel bed 5 may be controlled. Typically the flow rate will be increased along the length of the main chamber 23.

In each fluidisation section 37, water flows from discreet reservoir compartment 39 into the main chamber 23 causing fluidisation of the mussel bed 5, enabling dissociation of sea squirts and other bycatch, which given their relatively low density become entrained in the water flow in that section 37 and are drawn with the water flow over section overflow weirs 17. Each section 37 further comprises a vane 43 to prevent sea squirts and other bycatch or detritus from moving along the length of vessel 1.

Thus a controllable flow of cleaned mussels is delivered to the second chamber 29.

Optionally, the first two section overflow weirs 17 may be effective in removing, say, sea squirts and bycatch (first weir) and detritus such as byssus (second weir) and the third fluidisation section is controlled, with increased water pressure, to selectively remove spats and immature mussels through third overflow weir 45 where they may be collected for use in re-tubing and placing on a re-set cultivation rope or line.

The invention has been described with reference to a preferred embodiment. However, it will be appreciated that variations and modifications can be effected by a person of ordinary skill in the art without departing from the scope of the invention.

Claims (27)

1. A method of removing tunicates and other bycatch from a population of cultivated shellfish, the method comprising:

disposing into a vessel a population of cultivated shellfish to provide a bed of cultivated shellfish, which vessel is configured for separation of tunicates and other bycatch from a bed of shellfish in a liquid medium and which has a liquid medium flow inlet;

passing a liquid medium through the bed of shellfish in the vessel via the liquid medium flow inlet;

providing a source of energy to the bed of shellfish in the vessel to disturb or move or fluidise the shellfish in the bed of shellfish and dissociate the tunicates and other bycatch therefrom; and removing the shellfish and/or the tunicates and other bycatch from the vessel.

2. A method as claimed in claim 1, wherein the source of energy comprises one or more flows of liquid medium directed into the bed of shellfish at a flow rate sufficient to impart energy to the bed of shellfish so as to disturb or move or fluidise the shellfish in the bed and/or dissociate the tunicates and other bycatch therefrom.

3. A method as claimed in claim 2, wherein the liquid medium is provided to the vessel at a lower portion of the vessel and directed into a shellfish bed arranged therein from below.

4. A method as claimed in claim 2 or claim 3, wherein the liquid medium is pumped into the vessel and into the shellfish bed at one or more locations by one or more pumps.

5. A method as claimed in any one of the preceding claims, wherein the liquid medium is water, preferably sea water.

6. A method as claimed in any one of the preceding claims, wherein the bed of shellfish are provided in a main chamber of the vessel and wherein fluidisation of the shellfish enables the shellfish to be moved along a length of a shellfish flow path in the vessel and into a second chamber or discharge tank, optionally separated from the main chamber by a barrier and wherein the shellfish are removed from the second chamber.

7. A method as claimed in any one of the preceding claims, wherein the dissociated tunicates are removed from the vessel.

8. A method as claimed in any one of the previous claims, which is a batch process.

9. A method as claimed in any one of claims 1 to 7, which is a continuous process.

10. A method as claimed in any one of the preceding claims, wherein the tunicates or bycatch comprises sea squirts.

11. A method as claimed in any one of the preceding claims, wherein the shellfish are cultivated mussels.

12. A method as claimed in claim 15, wherein the cultivated mussels are ropecultivated mussels.

13. A method as claimed in any one of claims 1 to 12, wherein the source of energy comprises a vibrating member disposed in relation to the bed of shellfish in the vessel to disturb or move or fluidise the shellfish in the bed of shellfish and dissociate the tunicate and other bycatch therefrom.

14. A method for recovering immature shellfish from a harvestable population, the method comprising the steps of any one of claims 1 to 13 and further comprising removing the immature shellfish for re-cultivation.

15. A method for thinning and re-tubing of mussels in a rope-based mussel cultivation system, the method comprising after one or two years of growth, deroping and de-clumping the population of cultivated mussels, removing any tunicate or bycatch according to the method of any one of claims 1 to 13, removing the dissociated mussels, grading the dissociated mussels and re-tubing a grade of dissociated mussels by placing onto a cultivation rope in a tubing step.

16. A system for the removal of tunicates and other bycatch from a population of cultivated shellfish the system comprising:

a vessel of a size and configured to receive a population of cultivated shellfish and having a base for forming a bed of cultivated shellfish on, the vessel having at least one liquid medium flow inlet for providing inflow of a liquid medium to the vessel; and a perturbation energy means for providing to the vessel sufficient energy to disturb or move or fluidise shellfish in a bed of shellfish and dissociate the tunicate and other bycatch therefrom.

17. A system as claimed in claim 16, wherein the vessel comprises at least one liquid medium flow inlet in a lower portion thereof and the perturbation energy means comprises at least one pump configured to pump the liquid medium into the at least one flow inlet at a sufficient flow rate and/or pressure to disturb or move or fluidise shellfish in a bed of shellfish and dissociate the tunicates and other bycatch therefrom.

18. A system as claimed in claim 17, wherein the at least one liquid medium flow inlet is provided in a lower portion of the vessel and configured to direct a liquid medium into a shellfish bed arranged in the vessel from below.

19. A system as claimed in claim 16 or claim 17, wherein the base is a raised or suspended base.

20. A system as claimed in claim 19, wherein the vessel comprises, below the raised or suspended base, a sump or reservoir fed by one or more flow inlets and being configured to feed a plurality of liquid medium flows through the base via a plurality of inlet apertures in the base.

21. A system as claimed in any one of claims 16 to 20, wherein the vessel comprises a main chamber comprising the base onto which may be formed a bed of cultivated shellfish and a second chamber or discharge tank associated with the main chamber into which may be received shellfish from the main chamber that are free of dissociated tunicates and other bycatch.

22. A system as claimed in claim 21, wherein the second chamber or discharge tank and the main chamber are separated by weir and/or baffle.

23. A system as claimed in claim 21 or claim 22, wherein a grading mechanism is provided in association with the second chamber or discharge tank and/or between the second chamber or discharge tank and the main chamber, wherein the second chamber or discharge tank is preferably provided with a solids transfer device selected from a paddled conveyor or Archimedean screw.

24. A system as claimed in any one of claims 16 to 23, wherein the vessel is provided with one or a plurality of weirs, vanes or baffles to control movement of shellfish and/or to facilitate separation of tunicate and other bycatch.

25. A system as claimed in any one of claims 16 to 24, wherein the perturbation energy means comprises a vibrating member which comprises or is associated with the base.

26. A vessel for use in a system as defined in any one of claims 16 to 25, the vessel being of a size and configured to receive a population of cultivated shellfish and having a base for forming a bed of cultivated shellfish on, the vessel having at

5 least one liquid medium flow inlet for providing inflow of a liquid medium to the vessel.

27. A boat fitted with a system as defined in any of claims 16 to 25 or fitted with a vessel as defined in claim 26.