Note: Descriptions are shown in the official language in which they were submitted.
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APPARATUS AND METHOD FOR CULTIVATING
AQUATIC CRUSTACEANS AND MARINE SHELLFISH
FIELD OF THE INVENTION
The invention relates to an apparatus and method for the cultivation of
aquatic
s crustaceans and marine shellfish including marine bivalve mollusks. More
particularly, it
concerns methods for cultivation of juvenile mollusks (spat), such as
scallops, mussels,
clams and oysters, under conditions that greatly increase the yield of adult
mollusks per
unit area of cultivation whilst reducing personnel time spent in the
cultivation.
BACKGROUND OF THE INVENTION
io Historically commercial harvesting of mollusks, e.g., scallops, mussels,
clams and
oysters, etc., has been largely dependent on naturally available cultivation
terrain and
conditions. Thus, the majority of scallops, mussels, etc. are harvested from
naturally
existing areas in which the mollusks typically exist or are implanted.
Commercial
harvesters of mollusks have, in large, simply harvested mollusks as they
existed in nature
i5 or used naturally occurnng propagation areas for seeding for subsequently
harvesting.
Scallops, mussels, clams, oysters, and similar shellfish undergo complex
changes during
their initial stages of growth. In order to grow an economically significant
proportion of
a crop of spat to marketable size, two things are of basic importance: the
availability of
food; and protection of the spat from predators.
2 o A land-based hatchery/nursery provides protection, but must also provide
food for the
early, most vulnerable stages of the shellfish. As the juveniles grow, they
require more
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food so a condition of economic impracticality is reached. In many natural
situations, the
algae utilized as food is abundant, but predators also are abundant.
Enclosures may be
used as protection against predators, but fouling organisms grow rapidly under
such
conditions so the enclosures must be cleaned at regular intervals to ensure
adequate water
s circulation through the enclosures. The cleaning process is not only labour
intensive but
it results in increased mortality rates of the mollusks caused by motion
shock.
As most mollusks are bottom dwelling creatures, conventional enclosures are
bottom
oriented, e.g., cages, and have been labour intensive as regards cleaning and
sorting.
Culture systems, such as oriental string culture for oysters, may be
considered exceptions,
i o but are nevertheless labour intensive.
It has long been recognized that the "natural" form of mollusk cultivation and
harvesting
is highly inefficient for many reasons, e.g., the attack of predators on the
spat. Hence,
considerable work has been done to try to render the cultivation and
harvesting of
mollusks a more efficient operation as evidenced by the following U.S.
Patents.
i5 U.S. Patent No. 4,186,687 to Gilpatric issued Feb. 5, 1980 discloses a
method in which cultchless young oysters of a selected size taken from
seed stock are placed in a set of foraminous cribs where the young oysters are
protectively housed until they reach maturity.
U.S. Patent No. 4,377,987 to Satre issued Mar. 29, 1983 discloses a system for
growing
20 oysters comprising a vertical row of trays suspended from carrying ropes
and enveloped
by a protection net.
U.S. Patent No. 4,704,990 to Moxham issued Nov. 10, 1987 teaches a method and
apparatus for cultivating mollusks in a water permeable container which is
rotated to
prevent the build up of debris.
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U.S. Patent No. 3,741,159 to Halaunbrenner issued June 26, 1973 discloses a
float
equipped cage for shell-fish comprising a basket like receptacle incorporating
a float
means and means for attaching a line at the bottom thereof.
U.S Patent No. 3,316,881 to Fischer issued May 2, 1967 relates collecting and
setting
s spat with an artificial cultch material formed from plastic foamed sheets of
polyethylene
suitably coated or uncoated for collecting and promoting the set of shellfish
spat thereon.
U.S. Patent No. 4,196,694 to Buchanan issued Apr. 8, 1980 teaches a method of
construction of an artificial reef with individual reef elements manufactured
from
recycled or new materials. Each reef element is constructed from used tire
casings which
io are cut in one of several different ways.
U.S. Patent No. 3,909,971 to Wilde issued Oct 20, 1975 discloses an off bottom
oyster
culture system including a series of floating trays held by paired bridal
lines. The method
provides for a co-active operation of the tray and boat system, but still
requires extensive
cleaning and maintenance procedures.
i5 U.S. Patent No. 4,170,197 to Walker issued October 9, 1979 teaches a method
of raising
oysters that introduces the use of large gauge mesh which imparts some degree
of self
cleaning. The mollusks, however, require to be periodically flipped to remove
the fouling
organisms on the outer surfaces.
U.S. Patent No. 4,896,626 to Holt issued Jan 30, 1990 and relates to an
apparatus for the
a o cultchless cultivation of mollusks having a plurality of quadrilateral
compartments
connected together by cords in the form of a continuous belt. This apparatus
has the
advantage that various different sections of the belt can be lifted for
cleaning purposes,
thereby minimizing motion shock to other co-cultured mollusks. The apparatus
does
however require frequent cleaning and is therefore labour intensive.
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The Japanese lantern is widely used in the art for the cultivation of
mollusks, particularly
scallops. This apparatus comprises an elongate flexible netting structure,
with internal
netting compartments. The mollusks are introduced into the compartments
through a slit
in the netting that extends the length of the lantern. The lantern nets are
expensive and
have a limited lifespan. The removal of edible sized mollusks from the
lanterns is a
labour intensive process, requiring the manual removal from each compartment.
Similarly, the introduction of fresh spat and subsequent repair of the
lanterns is time
consuming and requires a slit the length of the lantern to be re-sewn. The
lanterns also
suffer from the disadvantage of readily silting up with organic debris.
io Although the aforementioned patents have promoted the development of
crustacean and
shellfish cultivation, the prior art apparatus and methods are predominantly
inefficient
and expensive.
SL'MMARY OF THE INVENTION
It is an object of the present invention to provide an apparatus and method
for cultivating
i5 aquatic crustacean and marine shellfish. In accordance with an aspect of
the instant
invention there is provided an apparatus for the cultivation of shellfish
comprising: a
suspending means located in part at the top of the apparatus to suspend the
apparatus in
water and in part at the bottom of the apparatus to prevent it from rocking
back and forth;
a top bracing means located at the top of the apparatus that co-operates with
the
2 o suspending means to stabilize the apparatus in the water thereby
minimizing movement; a
bracing means located between opposite corners of said apparatus to prevent
the
apparatus from collapsing in on itself; a barner means wherein the
permeability is
optimized through mesh size and strength to permit passage of water whilst
minimizing
build up of organic debris; and a plurality of supporting means vertically
spaced to
a 5 support said shellfish.
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In one embodiment of the invention there is provided a mollusk cage
comprising, a rigid
frame adapted at its upper surface to provide a brace structure, said rigid
frame further
comprising; a plurality of essentially vertical corner posts; a means of
connecting said
corner posts to other said corner posts; a plurality of internal trays forming
a series of
internal compartments within said rigid structure; and a mesh material
surrounding said
rigid frame and covering each of said internal trays.
In accordance with an embodiment of the invention the suspending means is
provided a
bladder buoy distantly attached to the upper surface of said brace and a
plurality of
anchor lines releasably and extendibly attached to the bottom of said corner
posts to
i o reduce motion shock.
A principal object of this invention is the provision of apparatus and a
method for the
cultivation of marine bivalve mollusks, in particular scallops.
The present invention therefore provides new apparatus and method that permits
the
cultivation and harvesting of mollusks to be much improved over prior methods
and
15 apparatus with the result that greatly improved quantities of marketable
mollusks can be
harvested for each unit of aquaculture area and unit amount of personnel time
expended
thereon as compared to what could be obtained prior to this invention.
Further objects include the provision of a new apparatus for cultivation of
juvenile
mollusks (spat) under protected conditions to greatly increase the yield of
adult mollusks
2 o per unit area of cultivation and personnel time spent in the cultivation.
The new
apparatus is particularly adapted for the cultivation of spat for deployment
in water
conditions conducive to rapid growth of the shellfish and protect them from
predators.
The mortality rate of the mollusks is decreased as they are removed from the
water and
handled less often, thus reducing physical shocks that each animal experiences
upon
2 5 being handled or removed from the water. The method of suspending the
apparatus, such
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that it is stable in the water, also contributes to the lower mortality rate.
It is a further object of the instant invention to provide an apparatus that
does not silt up,
is easily emptied and repaired. The gauge of the mesh has been chosen such
that it allows
organic materials to flow through the apparatus. The cage is also larger than
other prior
art cages. Again the method of suspension contributes to the lack of fouling
of the new
apparatus. The apparatus is therefore easily cleaned and capable of handling
the crop of
mollusks on a routine basis with low labour requirements and minimum exposure
of
workers to adverse weather conditions.
The design of the apparatus is such that it is highly space efficient on site.
Both the
io apparatus of the instant invention and the Japanese lantern are organized
on long strings.
On a string 100ft in length, it is possible to suspend approximately five of
the apparatus
of the instant invention. On average, the apparatus can hold about 4,000
scallops, i. e.
approximately 20,000 scallops per 100ft of line. In contrast, on a similar
100ft string, it
is possible to suspend approximately ten Japanese lanterns. On average, each
lantern can
i5 hold about 225 scallops, i.e. approximately 2,250 scallops per 100ft of
line. The strings
are usually spaced about 75ft apart, irrespective of whether they are carrying
the
apparatus of the invention or the lanterns of the prior art.
The labour costs associated with the apparatus and the methods disclosed
herein are
greatly reduced. This is partially due to the fact that fewer cages, with more
mollusks in
2 o each cage, are being handled, but also because the removal of the mollusks
is achieved
more efficiently. The rigidity of the apparatus allows the apparatus to be
tilted, which
allows the mollusks to be tipped out when they are of an edible size.
Additionally, there
is much less sewing involved with the apparatus of the instant invention to
close up the
horizontal slits after the fresh spat are introduced.
In a preferred embodiment, the new apparatus or cage comprises: an essentially
CA 02239043 1998-OS-29
rectangular frame; a top support brace which provides support for the cage
while
suspended; a top and bottom "x" brace which prevents the cage from collapsing
in on
itself; a series of shelves arranged within the cage; and a specific gauge of
mesh, used to
cover the frame and each of the shelves, which is large enough to prevent
fouling of the
cage and small enough to prevent the mollusks from escaping.
In a further preferred embodiment, the stabilizing buoy is attached at a
predetermined
distance from the top of the support brace, and anchoring weights are
extendibly attached
to the bottom of the cage to reduce motion shock.
BRIEF DESCRIPTION OF THE DRAWINGS
io A more complete understanding of the invention may be obtained by reference
to the
accompanying drawings in which:
FIGURE 1: is a perspective view, of the mollusk cultivation apparatus of the
invention.
TABLE 1: shows the growth rate of sea scallops in Japanese lantern.
TABLE 2: shows the growth rate of sea scallops in the apparatus of the instant
invention.
is DESCRIPTION OF THE PREFERRED EMBODIMENTS
The apparatus of the invention comprises:
Corner Posts 10 and Top Support Brace 12; This part of the cage is made of
1/4" angle
iron, 1/8 of an inch thick. It is painted, as is the rest of the metal on the
cage with an anti-
fouling paint. The top support brace 12, is welded together at the top 14, to
from a
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pyramid, indicated generally at 16. A line, extends from the top of the
support brace 14
to the surface of the water. The top support brace serves to stabilize the
cage in the water
and prevent it from rocking backward and forward. Angle iron is preferably
used for the
corner posts 10, as the frame for the bottom of the cage 22, and the frame for
each of the
trays 24, are placed inside the angle iron and welded in place. Each corner
post is
continuous with its adjacent section of the top support brace, each being
fabricated from a
single piece of metal. The corner posts 10 being bent at the appropriate
position 26, to
form the pyramid 16.
Top and Bottom "X" Braces; These braces, indicated at 28 and 30 respectively,
run
io approximately between opposite corner posts at the top and bottom of the
cage. They are
made of 3/8" square stock steel. They are welded in the middle 32, where they
meet.
They are also welded to the top and bottom trays about 1" from the inside
angle at the top
and at the bottom of each corner post. The braces provide the cage with the
necessary
rigidity.
is Trays, indicated at 34, are made of 3/8" square steel stock. The trays are
constructed of
four sections or sides 36, each cut on the ends at 45° angles. The ends
38, are then fitted
together to form a square, and the individual sides are welded together. The
trays are
then welded to the inside angle of each of the four corner posts. In the
preferred
embodiment, the trays are approximately 9" apart.
a o Mesh material used to cover the apparatus or cage of the instant invention
is 1/2"
TenexTM mesh. This mesh has the appropriate combination of mesh size and
strength for
the cages. The mesh is applied in two phases; in the first phase, the mesh is
streched
from one side of the tray to the other. This tray mesh is then folded around
each of the
pieces of 3/8" square stock steel that form each section of the tray. Tuna
line is then
a s woven through the mesh, where it overlaps with itself, on the outer facing
of the 3/8"
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square stock steel that forms the sides of each tray. The fact that the weave
is on the
outside face of the 3/8" square steel stock is important because it supports
more evenly
the weight distribution of the mollusks on the mesh of each tray, thereby
allowing the
cage to be lifted without putting undue strain on either the frame or the
mesh.
s Eaeh side of the cage is then covered in a single sheet of mesh. The sheet
of mesh is
folded over the 3/8" square stock steel that comprises the top tray or level
of the cage. In
a preferred embodiment a 9mm nylon line is then woven in and out of the mesh
that is
wrapped around the top tray and the weaving is done so that the nylon line
passes around
the 3/8" square steel stock that forms the sections or sides of each top tray.
Horizontal
to slits are then cut into the mesh on each side, at the level of each of the
trays. Access
mesh, that protrudes past the corner posts on each side is then tucked inside
each of the
four corner posts, thereby protecting mesh from mechanical damage during the
lifting of
the cages. Once the side mesh has been installed on each side of the cage, the
overlapping pieces of mesh from the adjacent sides are sewn together.
is The spat are introduced into each tray of the apparatus through additional
horizontal slits
that are cut approximately parallel to each tray. The spat are evenly
distributed across the
tray and the slits, which are typically 12" or less, are sewn up with suitable
line or thread.
Upon harvesting, the line or thread is removed, the rigid structure is tilted
and the edible
sized mollusks are tipped out. The rigidity of the structure, and the small
horizontal slits
2 o in the mesh, thereby providing for quick and easy harvesting of the
mollusks.
The preferred method of the instant invention provides a means of decreasing
the
mortality and growth rates and reducing the build up of organic debris in the
apparatus.
This is achieved by suspending the apparatus of the instant invention at the
maximum
depth of water that has the best combination of warmth, little current, high
levels of
2 s nutrients in the water and little organic fouling material.
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The preferred method of suspension comprises:
A surface line; that is tied to the apex of the pyramid that forms the top of
the support
brace. Approximately 2 to 3 feet above the apex of the support brace there is
attached a
bladder buoy, which is encircled by the surface line. In a preferred
embodiment the buoy
s is 50" in circumference. The air pressure inside the buoy is 15 lbs per
square inch. The
buoy bears the weight of the cage and holds it at the desired height above the
bottom.
The remainder of the line, from the bladder buoy to the surface is slack and
tied at the top
to what is known as a headline or longline. The headline or longline streches
across the
surface of the water in a straight line and has any number of surface lines
attached to it.
io A small stryofoam buoy is attached to the headline to hold up the headline
and the surface
line. The use of the bladder buoy to bear the weight of the cage is extremely
important,
as it prevents the cage from being affected by the wave action of current
action on the
surface or just below the surface of the water. At the depths which the
bladder buoy can
be located there is considerably less movement in the water so the cage is
considerably
i5 more stable. The bladder buoy was chosen as opposed to other floatation
devices because
of the ability of air to bear more weight that other materials and because of
the fact that it
never becomes waterlogged.
Anchor Lines; which are tied to each corner of the bottom of the cage. They
are a series
of lines extending from the cage to the ocean bottom. At the ocean bottom, the
lines are
2 o attached either to sand bags or to cement blocks. Sand bags are preferred
on muddy
bottoms, whereas cement blocks are preferred on rocky bottoms due to greater
wave
action. The anchor line must be tight not slack. While the bladder buoy is
designed to
hold the cage up in water, the anchor lines are designed to hold the cage
firmly in place
and to prevent it from moving or drifting. The weight of the cement blocks or
sand bags
2 s should be at least 1001bs. Along each of the anchor lines there may be one
or more
splices, loops that consist of part of the lines that have been spliced. On
the cage, on each
of the four corners near to where the anchor lines are tied, there are four
metal hooks
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which are welded to the cage. Thereby, when it is desired to adjust the height
of the cage
in the water by lowering it, it is possible to bring the cage to the surface
and hook one or
more of the loops that is tied at the desired height into the hooks on the
four corners of
the cage, thereby shortening the anchor line, provided that more slack is paid
out of the
surface line. The ability to adjust the distance the cage is from the bottom
is important
because in the winter the water is warmer at a lower depth. In the summer the
water is
warmer at a higher depth, and the maximum growth rate is achieved by
positioning the
mollusks in the warmest water available.
Example 1
io A comparison of the growth response of sea scallops in the traditional
Japanese lanterns
and the cages of the instant invention were conducted over a one year time
period. Sea
scallops were contained in twenty five Japanese lantern nets and twenty five
cages of the
invention. They were attached alternately to a 110m head rope. The head rope
was
suspended at 1 lm from the surface, Sm off the bottom. Scallop spat (20 to
25mm) were
i5 stocked into the cages and nets at commercial densities. Bimonthly shell
measurements
and monthly tissue samples were obtained from subsamples. The mesh sizes of
the cages
and the lantern nets used throughout the fall and winter experimental period
was 8mm.
The scallops were than transferred to cages and lantern nets with 2lmm mesh in
the late
spring.
a o The following parameters were monitored (and statistically analyzed) as
part of the study
over a one year period:
(i) average shell heights were taken bimonthly;
(ii) soft tissue wet and dry determinations (individual wet weights of
adductor muscle
and remaining tissue) were taken monthly;
2 s (iii) temperature and salinity records at the experimental site were also
obtained
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monthly; and
(iv) wind directions and velocities for the area were obtained from
Environment
Canada on a monthly basis.
The objective of this experiment was to determine if the apparatus and method
of the
instant invention of the traditional Japanese lantern nets provide better sea
scallop growth
in commercial sea scallop aquaculture.
The results, shown in Tables 1 and 2, demonstrate that the new apparatus
reduces the
time period required for the mollusks to reach a marketable size and hence
generate an
earlier cash flow. The experiment also demonstrated that the new apparatus
imporves the
io cost effectiveness of aquaculture of mollusk operations whilst reducing
dependence on
expensive imported lantern nets.
The foregoing has outlined some of the more pertinent objects of the present
invention.
These objects should be construed as being merely illustrative of some of the
more
prominent features and applications of the invention. Many other beneficial
results can
is be obtained by applying the disclosed invention in a different manner or
modifying the
invention within the scope of the invention. Accordingly other objects and a
full
understanding of the invention may be had by refernng to the summary of the
invention,
the detailed description describing the preferred embodiments in addition to
the scope of
the invention defined by the claims taken in conjunction with the accompanying
z o drawings.
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