Method of cultivating shellfish

The invention relates to the cultivation of shellfish. A first type of shellfish capable of securing themselves to a cultch such as by producing byssus are seeded onto a culture rope together with a second type of shellfish which are not capable of securing themselves. The seeding process is carried out using a seeding machine, and the shellfish are retained against the culture rope by way of a seeding stocking. The seeding stocking, the culture rope, and all of the shellfish, are then transferred to a suitable environment for cultivation. The first type of shellfish produce byssus and thereby secure themselves to the culture rope. The second type of shellfish are also secured by way of the byssus produced by the first type of shellfish. The seeding stocking is then no longer required and degrades or is burst by both types of the shellfish.

TECHNICAL FIELD 
This invention relates to the cultivation of shell fish, particularly 
shellfish such as scallops, oysters or the like which do not naturally 
produce means for securing themselves indefinitely to a suitable 
cultivation support means, and also shellfish such as mussels which do 
naturally produce means for indefinitely securing themselves to a suitable 
cultivation support means. 
The term securement means as used herein should be interpreted as a means 
which is produced by a shellfish and is suitable for enabling the 
shellfish to be indefinitely and reliably secured to a cultivation support 
means for cultivation purposes. The term should not be interpreted to mean 
for example the cement gland of an oyster. 
The term retaining means as used herein should be interpreted as a means 
suitable for retaining shellfish to a cultivation support means for a 
limited amount of time, whereby the retaining means is capable of being 
burst by the growing shellfish or is capable of degrading over time such 
that it is at least substantially wasted by the time the shellfish are of 
a harvestable size. 
BACKGROUND ART 
Various methods for the cultivation of scallops, oysters and other like 
shellfish are known in the art; see for example the disclosures of New 
Zealand Patent Specifications 164532, 165145 and 207152. Broadly speaking, 
these methods may be divided into two distinct groups, namely, those in 
which the shellfish are distributed loosely in baskets, cages, mesh 
floored trays or the like, and those in which each shell fish is secured 
to a suitable cultivation support means such as, for example, a culture 
rope or tarred stick. In conventional scallop or oyster farming, where the 
second of these cultivation methods is used, artificial retaining devices, 
such as plastic or metal pins, monofilament nylon, metal rings or chemical 
adhesive must be used to secure the growing shellfish to the culture rope 
or the like. 
It will be appreciated that there are significant disadvantages inherent in 
each of the two above mentioned broadly stated methods of shellfish 
cultivation. Briefly, among the more obvious disadvantages is the high 
cost of equipment and/or labour in setting up and maintaining a shellfish 
farm which relies on any of these known methods of cultivation. For 
example, where the shellfish are loosely distributed in baskets or the 
like the capital outlay for equipment is high and the equipment requires 
on-going maintenance, further, the shellfish require frequent manual 
servicing in the form of respreading and removal of marine fouling 
organisms etc. While the capital cost of equipment may be lower for farms 
cultivating shellfish where the shellfish are secured to cultivation 
support means high labour costs are incurred in setting up the farming 
operation as each shellfish must be individually secured to the culture 
rope or the like. 
DISCLOSURE OF INVENTION 
Accordingly, in a first broad aspect of the present invention there is 
provided a method of cultivating shellfish, wherein the improvement 
comprises retaining a plurality of live juvenile shellfish on a 
cultivation support means by way of a retaining means, said plurality of 
shellfish comprising a first type of shellfish having the potential for 
producing securement means at a future date such that said first type of 
shellfish can become secured to said support means by said securement 
means, said plurality of shellfish also comprising a second type of 
shellfish not having the potential for producing securement means, wherein 
said second type of shellfish can become secured to said support means by 
way of said securement means when said securement means has been produced 
by said first type of shellfish. 
In a further embodiment of the invention there is provided a method 
according to the immediately preceding paragraph wherein said plurality of 
shellfish are placed in a suitable cultivation medium after said plurality 
of shellfish have been retained in said support means by said retaining 
means, and said plurality of shellfish are allowed to grow such that 
securement means is produced by said first type of shellfish wherein the 
securement means secures said first type of shellfish to said support 
means. 
In a further embodiment of the invention there is provided a method in 
accordance with any one of the two immediately preceding paragraphs 
wherein said securement means is allowed to become secured to said second 
type of shellfish after said securement means has been produced by said 
first type of shellfish. 
In a further embodiment of the invention there is provided a method in 
accordance, with any one of the three immediately preceding paragraphs 
wherein said retaining means is allowed to become at least substantially 
wasted after said second type of shellfish becomes secured to said 
securement means. 
According to a further aspect of the invention there is provided a 
plurality of shellfish prepared in accordance with any one of the four 
immediately preceding paragraphs. 
In a preferred embodiment of the present invention juvenile mussels are 
combined with other juvenile shellfish such as scallops, oysters or the 
like which do not naturally produce means for securing themselves to a 
suitable cultivation means and/or rock oysters or other such shellfish 
which do naturally, at least initially, produce means for securing 
themselves but which can also be grown free of attachment. The mussels 
provide the means of securing the other shellfish to the cultivation 
support means. In this regard, mussels naturally secrete byssus, a mass of 
strong threads used by mussels for attaching themselves to a support 
surface. In addition to binding each mussel to the culture rope the 
secreted byssus also binds to the shellfish adjacent the mussel, thus 
providing the means for securing the other shellfish to the cultivation 
support means. It will be appreciated that the present invention provides 
significant advantages over the methods of the prior art in terms of both 
cost and simplicity.

BEST MODES FOR CARRYING OUT THE INVENTION 
As illustrated in the drawing, a seeding machine 1 comprises a hopper 2 
having a base which is substantially funnel shaped and which narrows down 
to an exit region terminating in a seeding tube 3. In preparation for 
operation of the seeding machine 1 a mesh-like seeding stocking 4 is 
stretched over and gathered about the seeding tube 3. 
To produce a seeded rope ready for stringing out in a shellfish farm an end 
of a culture rope 5 is inserted into the hopper 2 and passed through the 
seeding tube 3. An end of the seeding stocking 4 is then closed around the 
rope 5. 
A volume of live juvenile mussels and scallops are obtained, preferably in 
a ratio of at least three mussels per scallop, and are combined in such a 
manner that the juvenile scallops are substantially evenly dispersed 
within the mass of juvenile mussels. This substantially mixture of 
shellfish 6 is placed in the hopper 2. The shellfish 6 pass from the 
hopper 2 down the seeding tube 3 and surround the culture rope 5. The 
culture rope 5 is gradually pulled through the hopper 2 and seeding tube 
3, dragging with it the seeding stocking 4. The shellfish 6 fall down 
through the seeding tube 3 into the seeding stocking 4 to surround the 
culture rope 5, the seeding stocking 4 retaining the shellfish 6 against 
the culture rope 5. 
When the desired length of the culture rope 5 has been seeded with 
shellfish 6 the seeding stocking 4 is tied off and the remaining length of 
culture rope 5 removed from the seeding machine 1. The seeding stocking 4 
should be maintained in a tensioned condition during the seeding operation 
otherwise clumps of shellfish occur. 
Apparatus used to perform the seeding method of the present invention may 
be substantially similar to that used for seeding mussels alone although 
minor adaptions may be required. For example, particular control must be 
exercised over the mixing of the shellfish, therefore a further feed 
system or manual placement for the second shellfish type may be required. 
As indicated above an even distribution of the shellfish is desirable. The 
reason for this is that better production yields are obtained. If the 
shellfish are not combined before being introduced into the seeding 
machine 1 a two belt feed system may be used to deliver the shellfish to 
the seeding tube 3. Alternatively, if the seeding machine 1 forms part of 
a small scale operation comprising in the main a seeding table the two 
types of shellfish may be placed by hand, e.g. mussels by the left hand 
and scallops by the right hand. 
Each seeded rope can then be hung out on conventional long line rafts or 
other similar structures in a suitable environment for the shellfish to 
grow to a harvestable size. During the growth period, which can be between 
ten and twentyfour months, the seeding stocking 4 is burst by the growing 
shellfish or gradually degrades and disintegrates. During this time the 
mussels secrete byssus to secure themselves in place. During this process 
it has been found that the mussels bond both themselves and the scallops 
to the culture rope 5. Typically, the seeding stocking 4 is made from 
cotton or polyester/cotton mix, however, it will be appreciated that any 
other suitable material which either degrades fully, or at least 
sufficiently to allow the growing shellfish to burst through may be used. 
Other means for retaining the shellfish about the culture rope while the 
mussels secretes sufficient byssus to bind themselves and the scallops to 
the rope include "Spanish Lace", i.e. a strip of woven material such as 
cotton, rayon, polyester, nylon or mixes of these. 
A suitable rope 5 would be between 10-15 mm diameter having a trim or 
fluffy medium on its surface so that the mussels can grip securely. Other 
acceptable rope types include plain black rope having a soft, medium or 
hard surface layer, and knitted rope. 
As mentioned above, it has been found that in the case of scallops it is 
sufficient to use as little as three mussels per scallop. It will be 
appreciated that the above method is also applicable to other kinds of 
shellfish, and that the required number of mussels to bind the particular 
desired shellfish will depend on the size and shape of the shellfish in 
question. Other factors of influence will be the time of year, water 
temperature, location--i.e. rough or smooth water in the cultivation area, 
tidal currents, and the particular species of mussel used to provide the 
attachment medium. 
Although the above described embodiment uses a culture rope 5 to provide 
the cultivation support means it will be appreciated that lengths of 
tarred stick, bamboo poles, palm stakes, rows of poles (bouchots), cut 
down trawl netting, trim from polypropylene sacks, or any other such 
durable support material may be used in its place. 
Shellfish such as juvenile oysters (spat) which do not have the potential 
to produce byssus or an equivalent securement means are often able to 
temporarily attach themselves to a culture rope by way of their cement 
gland. Attachment to a culture rope in this manner is not reliable as the 
oysters may leave the rope at any time. In calm water conditions it is 
possible for an oyster to remain attached by way of its cement gland for 
up to two years, however the attachment does not provide a reliable way of 
retaining oysters while they develop. 
In a further embodiment of the invention a culture rope is placed in a 
suitable location such that non-byssus producing juvenile oysters attach 
themselves to the rope by way of the cement glands. The non-byssus 
producing shellfish could be sourced from a hatchery or could be obtained 
naturally or artificially from the wild. The culture rope is then seeded 
with byssus producing shellfish such as mussels using a seeding machine as 
described previously. The mussels are thus seeded onto the culture rope 
over the juvenile oysters and both are retained in position by a seeding 
stocking as also described previously. The seeded culture rope is then 
placed in a suitable cultivation area while the juvenile oysters and 
mussels develop. As the mussels develop they produce byssus and thereby 
secure themselves to the culture rope. The oysters are also secured by the 
byssus which is produced by the mussels. The mussels and the oysters are 
thus able to remain associated with the culture rope without the seeding 
stocking. The seeding stocking then degrades or is burst such that it is 
at least substantially wasted at the time of harvest. 
It should be appreciated that this further embodiment of the invention is 
not limited to use with only mussels and oysters. For example, the mussels 
can be substituted by any shellfish capable of producing a securement 
means similar to byssus. Similarly, juvenile scallops may be used in 
preference to the juvenile oysters. 
Examples of shellfish which are able to temporarily attach themselves to a 
culture rope include rock oysters such as Crassostrea gigas, Crassostrea 
virginica and Crassostrea commercialis. Further examples include flat or 
dredge oysters such as Tiostrea lutaria (also called Tiostrea chilensis), 
ostrea angasi and austrea edulis. 
Additional advantages of the present invention will become apparent to 
those skilled in the art after considering the principles in particular 
form as discussed and illustrated. 
Accordingly, it will be appreciated that changes may be made to the above 
described embodiment of the invention without departing from the 
principles taught herein. 
Finally, it will be understood that this invention is not limited to the 
particular embodiments described or indicated but is intended to cover all 
alterations, additions, or modifications which are within the scope of the 
appended claims.