Animal husbandry – Aquatic animal culturing – Fish culturing
Reexamination Certificate
2000-09-11
2002-11-19
Price, Thomas (Department: 3643)
Animal husbandry
Aquatic animal culturing
Fish culturing
Reexamination Certificate
active
06481378
ABSTRACT:
FIELD AND BACKGROUND OF THE INVENTION
The present invention relates to systems for farming aquatic animals in cages and, more particularly, to fish farming systems having a cage which can be submerged and refloated as desired, and to a method for submerging and refloating a fish cage as desired. While specifically referring hereafter to “fish”, it is understood that the farming system of the present invention may be used to raise other aquatic animals, e.g. shrimp, oysters, etc.
Considerable efforts have been made in an attempt to supply the rapidly increasing worldwide demand for fish protein. In addition to increasingly sophisticated open sea fishing, a significant fraction of the fish on the market today is raised and harvested using modern aquaculture techniques. Various fish farms have been successfully operating in large man-made pools. However, these farms are expensive to build and operate and do not always make it possible to reproduce optimal conditions for the growth of the fish.
More recently, fish farming has been increasingly carried out in large cages, which are made to float near or at the water surface just offshore (hereinafter “near shore”) in seas, lakes or other natural bodies of water. A fish cage system includes one or more large cages which are typically constructed of a rigid frame of some suitable shape and covered by netting which allows water to flow freely into and out of the cage, but which is of sufficiently fine mesh as to retain the fish inside the cage.
The advantage of such fish cage systems is that they do not take up scarce real estate and do not require the building of an expensive pool. Furthermore, the water conditions (e.g., salinity, temperature, oxygen content, and the like) approximate natural conditions in the open body of water, and may be more optimal for the growth of the fish than conditions simulated in man-made onshore pools.
While the near shore deployment of such fish cages is convenient in terms of accessibility, such deployment suffers from certain disadvantages. As near shore aquaculture develops there is an increasing shortage of quality sites in which to locate additional cages. Many sites suffer from oxygen depletion caused by fish waste and uneaten fish food as well as from industrial, agricultural and domestic runoffs from the nearby shore.
It is therefore often advantageous to avoid onshore locations and to locate the cages farther offshore, in what will be referred to hereafter generically as “deep waters”, i.e. in areas, which are not adversely affected by runoffs and where the greater water circulation serves to dilute fish farm wastes.
However, locating fish cage systems in locations that are remote from the shore poses certain problems. Chief among these is the need to ensure the seaworthiness of the fish cage system in conditions, such as large waves and strong winds during storms, which may be much more severe than those experienced by near shore structures.
Furthermore, it is known that during storms when the water near the water surface is particularly turbulent, fish, which normally spend most of the their time near the water surface where the supply of oxygen is most abundant, tend to temporarily relocate themselves away from the surface to depths where the water is relatively unaffected by the storm and thus avoid damage and stress to themselves.
To minimize or eliminate damage to both the fish and the cages, several fish cage systems have been developed which make it possible to submerge the fish cage to a certain depth when desired, e.g., prior to the onset of a storm, to avoid cold surface water and/or surface ice in winter and hot surface water in summer, or to avoid various toxic contaminants, such as toxic plankton blooms or an oil spill. Zemach et al. in U.S. Pat. No. 5,412,903 which is incorporated herein for all purposes as if fully set henceforth, describe several such previous cage systems, and propose a fish cage system which overcomes some major previous disadvantages and limitations.
FIGS. 1 and 2
depict schematically a prior art fish cage according to Zemach et al. in '903, in which some of the original details have been omitted.
FIG. 1
shows a fish cage
100
, typically made of a metal skeleton structure on which is superimposed a netting
102
(shown partially) of suitable mesh size which allows water to flow freely through cage
100
but does not allow fish inside cage
100
to escape. Attached to cage
100
are one or more fish cage cables
104
. Cage
100
and cables
104
have combined upward buoyancy imparted through buoyancy chambers or members
106
, which ensures that at least, the upper part of cage
100
floats at or above the surface of the water. In cases requiring the temporary lowering of cage
100
to a certain depth, the system is further equipped with a sinker
108
which is connected to cable
104
. According to '903, in a basic embodiment sinker
108
is of fixed and invariable weight which is selected to overcome the combined net buoyancy of cage
100
and cage cables
104
described above, so that when the weight of sinker
108
is added to fish cage
100
and fish cage cables
104
the result is the submersion, preferably at a slow and controlled rate, of cage
100
. In another embodiment, sinker
108
is of variable buoyancy, with means provided to increase the buoyancy by introducing air, and to reduce the buoyancy by releasing air, even when sinker
108
is submerged.
Sinker
108
is further connected to a sinker cable
110
, which is also connected to a buoy
112
of any suitable design. Buoy
112
is designed to float at the water surface under all conditions. Buoy
112
is equipped with means for alternately shortening and lengthening the effective length of sinker cable
110
, means which is preferably a suitable winch mechanism
113
housed within buoy
112
, typically one which is operated by an internal combustion engine.
During normal operations, cage
100
is allowed to float at the water surface, as shown in FIG.
1
. As described above, the buoyancy of cage
100
(plus fish cage cables
104
) is such that cage
100
remains at the water surface. In this condition no external forces are exerted on fish cage cables
104
which stay slack in the water, since sinker
108
to which they are also connected is being fully supported by buoy
112
, through sinker cable
110
which is taut (FIG.
1
). Buoy
112
is designed to have sufficient buoyancy to support sinker
108
(and sinker cable
110
) while still floating at the water surface.
Whenever it desired to submerge cage
100
, sinker cable
110
is allowed to lengthen, preferably at a controlled rate, by, for example, releasing a brake mechanism on the winch
113
housed in buoy
112
. The weight of sinker
108
then pulls sinker cable
110
out of winch
113
, causing it to lengthen as sinker
108
goes deeper. As sinker
108
continues to go deeper there comes a point when fish cage cables
104
become taut, shifting the weight of sinker
108
from sinker cable
110
, which becomes slack, to fish cage cables
104
which become taut. Beyond this point, the full weight of sinker
108
is exerted on cage
100
. As described above, the incremental weight of sinker
108
is sufficient to overcome the buoyancy of cage
100
and brings about the submersion of cage
100
, as shown in
FIG. 2
of the prior art.
Preferably, the submersion takes place at a slow rate in order to minimize or eliminate damage to the structures and to the fish. Such a slow rate of submersion can be assured, for example, by carefully selecting the weight of sinker
108
so that the combined weight of the system is just slightly larger than the upwardly directed buoyancy forces. The submersion of cage
100
continues as long as sinker
108
exerts forces on cage
100
. As soon as sinker
108
hits bottom these forces are eliminated and cage
100
ceases to move downwardly. Instead, cage
100
stabilizes at a location, which is determined by the length of fish cage cables
104
(FIG.
2
).
The system described in '903
Fishfarm Tech Ltd.
Friedman Mark M.
Price Thomas
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