WO1989000004A1

WO1989000004A1 - Mollusc growing system and method

Info

Publication number: WO1989000004A1
Application number: PCT/AU1988/000197
Authority: WO
Inventors: Lawrence John Lardner
Original assignee: Lawrence John Lardner
Priority date: 1987-06-29
Filing date: 1988-06-22
Publication date: 1989-01-12

Abstract

An oyster growing system including a platform (1) supported buoyantly by tanks (2). Oyster racks are attached in a stack to the platform (1) which is lowered into the water by bleeding air from the tanks (2) and raised by pumping air into tanks (2). The platform (1) includes guides (7) which run along vertical poles (8). The oysters can be kept submerged for their entire growing period, for further growth, where conditions allow.

Description

"MOLLUSC GROWING SYSTEM AND METHOD" This invention relates to a system for the cultivation of molluscs in particular oysters. Background Art Oysters are grown in many parts of the world and generally in the same manner. Large racks are erected in relatively shallow water at a height between high and low tide depths. This systems has disadvantages in that the oysters are only grown in one level thus inefficiently using water depth. Furthermore, the oysters are easily stolen or eaten by birds at low tide. Another problem associated with this method of cultivation is loss through extremes of temperature, for example high summer daytime temperatures coinciding with low tide. The present invention provides an alternative method of cultivating molluscs with a view to ameliorating at least some of the disadvantages of the prior art. Summary of the Invention

Accordingly, in one broad form, the present invention may be said to provide a mollusc cultivating system comprising a mollusc support for securing growing molluscs in a three dimensional array, the support adapted for submersion in water; buoyancy means adapted to secure a said support and to be controllably raised or lowered relative to the water surface; and an anchor means so as to maintain the system substantially fixed in one location.

Preferably the mollusc support is a plurality of mutually attached racks stacked one atop the other. An alternative support is a number of parallel ropes strung out in a three-dimensional array.

Normally the apparatus is lowered to the water bed and in this case the negative buoyancy may be used as the anchor means. Some mollusc varieties feed best in the upper 1 metre or so of the water where their plankton food is plentiful and for such molluscs, or for other reasons where applicable (deep water cultivation), the flotation means can further include surface floats normally partially submerged. These surface floats maintain the racks at the desired depth irrespective of tidal movement. This height maintenance can also be effected by using pins or other stops in vertical poles sunk into the water bed. Such rigid poles can advantageously be used as anchor means, although moorings and flexible lines (rope, chain, cable) can also be used for this purpose. By way of further explanation of the utility of the invention preferred features not necessarily essential to the invention, will now be described.

A main advantage of the invention is that the cultivating system allows the growing oysters to be in the water and feeding most of the time. Oysters feed by filtering material from the water and thus in the conventional system, where they are out of the water for approximately half their life, grow much more slowly than oysters submerged for the majority of their life. Thus there is provided a plurality of stackable racks adapted to be secured one to the other and, while stacked one atop the other, to accept a layer of oysters in each rack. The stacking of the racks also provides security for the oysters against attack by marine predators such as bream. Also the stacked racks may be locked together to prevent theft of oysters.

The bottom rack of the stack fits atop a platform having inflatable buoyancy devices being either collapsible or rigid. The buoyancy devices can well be integral with the platform or attached thereto.

Further provided is a controllable compressed air source such as a petrol motor driven compressor, or tanked compressed air, which is carried in the oyster grower's punt and attachable by airline to the buoyancy devices. Introduction of the compressed air into the buoyancy devices will displace water and allow the stack of oyster racks to be raised. By release of the air from the buoyancy devices the racks can likewise be controllably lowered. There can also be provided surface buoyancy devices designed to float partially submerged at the water surface. The surface devices maintain the racks at the desired feeding depth.

Anchoring means can be provided in the form of a framework in which the stacked racks can vertically move. The framework is anchored in the desired location by driving vertical frame work members into the bottom. The preferred system also includes a specially adapted barge. A petrol driven air compressor and associated manifold with a plurality of air connections is carried in the barge. Individual air lines are permanently connected to their respective buoyancy tanks (or each line might feed a number of linked tanks) and include at their free ends other connections suitable for connection to the air manifold. The barge includes an area to carry a number of stacks of oyster racks already coupled together and a suitable crane so they can be lifted from the barge onto the platform before the buoyancy device is flooded and the racks submerged. Unloading of the racks is accomplished by the reverse procedure.

Although not frequently required the system can also include temperature sensing devices and a programmed control unit so that if the oysters are above the water level and their temperature is above a predetermined critical level, then the racks will be lowered, by buoyancy adjustment, into the water thus submerging the oysters to a predetermined depth. Further, the controller can raise the oysters out of the water if the temperature probe determines that the water temperature is below some predetermined value while the air temperature is warmer. Pressure or wave sensors can also be used to lower the racks below the influence of rough surface conditions. Clearly in this embodiment the buoyancy devices are permanently connected to a pressured air source.

The control unit of the above described embodiment will also lift the oysters out of the water for the minimum period necessary for healthy growth, regular service or as required by the oyster grower . The emergence of the oysters obviously does not have to coincide with tidal movements and can therefore be conducted during periods of minimal exposure to predators and theft, or in accordance with favourable weather conditions. The exact performance of the system and therefore its degree of complexity will be best judged after considering the environmental details of its intended location.

Further exemplary features of the invention will now be described with reference to a preferred embodiment shown in the drawings which include: Brief Description of the Drawings

Fig. 1 showing a perspective view of a device adapted to carry stacked oyster racks in accordance with the invention; Fig. 2 showing a schematic plan view of the device of Fig. 1; and

Fig. 3 showing an air manifold and compressor used in conjunction with the device of Fig. 1. Description of Preferred Embodiment The exemplary apparatus includes a platform 1 sixteen buoyancy tanks 2 attached to its underside. A bundle of eight air lines extends from respective pairs of linked buoyancy tanks 2 to a plate 4 which has respective air connections 5 rigidly attached thereto, there being one air connection 5 for each of the linked pairs of buoyancy tanks 2.

A framework 6 is attached to the upper side of the platform 1 and encloses a volume dimensioned to fit a predetermined number of stackable oyster racks (not shown). The framework 6 includes convenient clamping means (not shown) for holding the stack of oyster racks firmly on the platform 1.

Extending from the corners of the platform 1 are respective guides 7 which fit over respective guideposts 8. The guideposts 8 are driven into the water bed at the location where the oysters are to be grown. The platform is positioned with each of the guides 7 encircling its respective guidepoεt 8. The platform 1 is then free to move vertically up and down relative to the guideposts 8 while it is restrained from any lateral movement. By this manner a number of platforms 1 may be positioned in a given area so long as there is left sufficient room to move the oyster growers barge alongside each of the platforms 1. Although not employed in this embodiment, some of the buoyancy tanks 2 may have an end extending outwardly from the platform 1 so as to present a bow shaped leading point and a generally catamaran type hull allowing the device to be easily towed behind the oyster growers barge. Once the platform 1 has been positioned relative to each guideposts 8 it is firstly maintained buoyant by sealing off the air connectors 5 while the buoyancy tanks 2 are substantially full of air. A barge carrying already stacked oyster racks filled with young oysters is brought alongside the platform 1. A crane aboard the barge is used to load onto the platform 1 the stacked oyster racks which are then secured to the framework 6.

The air connectors 5 attached to the plate 4 can be uncapped and linked to an air manifold 10 held on the barge and itself connected to a portable air compressor 11. The air manifold has bleed valves 12 or similar so as to let air bleed at a controllable rate from the buoyancy tanks 2. Where necessary selected ones of the buoyancy tanks 2 can be bled at a modified rate so as to maintain equilibrium in the attitude of platform 1. The buoyancy tanks 2 are equipped with perforations along their bottom edge so as to allow the ingress of water, and the air lines extend to a point at the top of the respective tanks thereby providing the controlled flooding of the buoyancy tanks 2 in response to the bleeding of air through the air connectors 5 and the attached air manifold 10. Once the platform has been submerged the air manifold 10 is disconnected from the air connectors 5 which are recapped to prevent the escape of further air, thuu maintaining a slight negative buoyancy and minimum weight on post brackets as well as preventing ingress of debris into the bundled air lines 3. The plate 4 and air connectors 5 are then lowered into the water and positioned so as to be easily retrievable at a later time by use of a conventional boat hook or similar grappling device.

When desired to do so the platform 1 is raised by bringing the oyster barge alongside the guideposts 8 and retrieving the plate 4 with its air connectors 5. The air connectors 5 are uncapped and connected to the air manifold 10 on the barge. The air compressor on the barge is then started and compressed air forced into the buoyancy tanks 2 through the bundled air lines 3. Bleeding of air from selected air lines through bleed valves 12 can be used in order to maintain a level attitude of the platform 1 as it begins to rise up the guideposts 8. hen the platform 1 has been brought to the surface the stacked oyster racks can be disconnected from the framework 6 and loaded onto the barge by use of its crane. Fresh racks with oysters can be then loaded on to the platform 1, or it might be left empty, before proceeding to another platform or returning to a suitable shed or wharf equipped to unload the oyster racks from the barge.

Under some circumstances the oysters might benefit from being raised clear of the water during their normal growing life while in the racks attached to the apparatus. For instance if mud worm is prevalent in a particular location, it might be found, by trial and error, that the effect of the mud worm can be greatly reduced by periodically raising the platform 1 to the surface and thus uncovering the growing oysters for some predetermined length of time.

Another problem sometimes encountered in growing preferred species of oysters, such as the Sydney Rock Oyster, is the infiltration of lower quality species, such as the Pacific Oyster, which can grow over and kill the commercial oyster. However the Pacific Oyster for example has a short life out of water and therefore can be eradicated by bringing the platform 1 to the surface for some days if the Pacific Oyster is known or thought to be intruding into the oyster growing area.

Other problems known to the experienced oyster grower such as Winter mortality and marine growth can also be ameliorated by appropriate use of this system. Under circumstances where for example a large number of platforms 1 are being used some distance from the unloading shed or wharf, as the case may be, it might be desired to tow the required number of platforms 1 already loaded with the stacked oysters to the growing area. The platforms 1 can then be disconnected from the "train" and attached to their respective guideposts 8 before being submerged in the normal manner. When harvesting the oysters the reverse procedure could be used.

Claims

CLAIMS :

1. A mollusc cultivating system comprising a mollusc support for securing growing molluscs in a three dimensional array, the support adapted for submersion in water; buoyancy means adapted to secure said support and to be controllably raised or lowered relative to the water surface; and an anchor means so as to maintain the system substantially fixed in one location.

2. A mollusc cultivating system as defined in claim 1 wherein the support is a plurality of racks securely stacked one atop the other and further including a rigid platform upon which the plurality of racks are adapted to be rigidly secured and below which is attached the buoyancy means.

3. A mollusc cultivating system as defined in claim 2 wherein the buoyancy means include a plurality of buoyancy tanks, or pairs of linked buoyancy tanks, each including a respective air line connection entering a respective tank and extending proximate a normally upper region thereof and through holes in a wall of the tank proximate a normally low region thereof so as to allow controlled flooding and evacuation of water from the buoyancy tanks by the forced ingress or controlled escape of air through the respective air lines.

4. A mollusc cultivating system as defined in claim 2 wherein the anchor means comprises a plurality of substantially vertical posts anchored relative to the water bed and a respective guide associated with each anchor post being rigidly connected relative to the buoyancy means and being slidable along the respective post.

5. A mollusc cultivating system as defined in Claim 4 wherein the posts include rigid supports defining the submerged height of the platform above the water bed.

6. A mollusc cultivating system as defined in claim 3 further including at free ends of the respective air lines a plurality of air connectors adapted to sealingly connect with corresponding connectors in an air manifold connected to a controlled pressured air supply.

7. A mollusc cultivating system as defined in claim 6 wherein the air manifold includes controllable air bleed devices and wherein the pressured air supply is a portable air compressor.

8. A method of cultivating molluscs by inserting young molluscs within a plurality of stacked racks, securing the racks to a platform including floodable buoyancy tanks, flooding the tanks so as to submerge the molluscs and anchoring the platform fixably in one location whereby the molluscs are retrieved by compressing air into the tanks so as to buoyantly raise the molluscs out of the water.

9. A method of cultivating molluscs as defined in claim

8 wherein the molluscs are buoyantly raised clear of the water at predetermined time intervals or at predetermined occasions corresponding to preselected circumstances.

10. A method of cultivating molluscs as defined in claim

9 wherein the predetermined circumstances include the occurrence of mud worm infestation, an alteration in water temperature or salinity, adverse wave action, marine growth, and/or the occurrence of unwanted species of molluscs.