DK202170018A1

DK202170018A1 - Cage for fish farming

Info

Publication number: DK202170018A1
Application number: DKPA202170018A
Authority: DK
Inventors: Melling Dag-Øyvind; Ludvigsen Tord
Original assignee: Roxel Aqua As
Priority date: 2018-07-10
Filing date: 2021-01-13
Publication date: 2021-01-22
Also published as: WO2020013703A1; GB2593026B; NO344480B1; GB202020255D0; GB2593026A; CL2021000016A1

Abstract

A fish-farming cage (1), the fish-farming cage (1) comprising a first buoyancy element (10) with a first diameter (D10), a second buoyancy element (20) with a second diameter (D20), a third buoyancy element (30) with a third diameter (D30), a closed enclosure (40) comprising a bottom wall (41) and a top wall (42), and an anchoring (50). In a lowered position, the second buoyancy element (2) is vertically displaceable in a water column relative to the first buoyancy element (10) when the first buoyancy element (10) is positioned in a water surface (0), the first buoyancy element (10) including a first work platform (11) and the second buoyancy element including a second work platform (21).

Description

. DK 2021 70018 A1

CAGE FOR FISH FARMING The invention relates to a fish-farming cage. The fish-farming cage comprises first, second and third buoyancy elements. The fish-farming cage may be submersible. The invention also relates to a method for moving the fish-farming cage along a water sur- s face and a method for crowding fish in the fish-farming cage. Background of the invention, prior art and the drawbacks thereof A conventional fish-farming facility generally comprises one or more floating cages. Each cage comprises an enclosure for the fish. By placing the cages in sheltered loca- tions, for example in fjords, they can be protected from the weather. A positioning like — that may have several drawbacks: There is less exchange of water than in locations exposed to the weather, so that uneaten feed and faecal matter may more easily ac- cumulate in a limited area, and in a concentration that may give a negative effect on the marine environment. Little exchange of water may also contribute to quicker foul- ing of the net forming an enclosure for the fish. Cages in sheltered locations may be obstructive to vessels moving in the area, and it is known that damage has been caused to cages by vessels and objects floating in the water. The vessel may be a ves- sel that collides with the cage because the vessel is off course or because the crew have not been aware of the cage. Such collisions may result in damage to the buoyan- cy element or the enclosure of a cage. A tear in the enclosure may result in fish escap- ing from the cage. Such a tear is typically caused by a propeller belonging to a vessel, for example a wellboat manoeuvring between several cages, or being in the process of positioning alongside a cage to delouse the fish or load fish ready for slaughter. By placing the cages in exposed locations, for example in the open sea offshore, the risk of damage from vessels is reduced, whereas the risk of damage due to wind and large waves increases, compared with cages placed in sheltered locations. Further,

, DK 2021 70018 A1 positioning offshore has the advantage of there being more space than inshore, good flow conditions and less infection pressure from pathogenic organisms.

Salmon in floating fish-farming facilities are exposed to salmon lice (Lepeophtheirus salmonis). The salmon louse is an external parasite on salmonoids and lives and mul- tiplies on salmon and trout in sea water. Salmon lice inflict wounds on the fish that may give infections, problems with the salt balance and that reduce the growth of the fish. Louse larvae, which are the infectious stage, are found primarily in the upper- most 10 metres below the water surface. Harmful algae that can secrete toxins may also be found in the uppermost part of the water column.

It is known to submerge a fish-farming cage below the water surface to reduce the loads that waves and wind may cause on the cage in bad weather, and to prevent at- tacks by salmon lice. To prevent attacks from salmon lice, the cage is typically sub- merged to more than 10 metres below the water surface. To prevent damage due to rough seas, the cage is typically submerged below an upper layer in the water column where the waves occur.

It is known that salmon take less nourishment if the water temperature is too low or too high. Optimum growth is achieved at a sea temperature of 15-16 °C. It is there- fore desirable to be able to position the vertical position of the cage in the water col- umn depending on the sea temperature, in order thereby to give the salmon the best possible growth conditions.

The salmon has an open swim bladder and the salmon therefore needs to go up to the water surface to gulp air for the swim bladder. When the air bladder is emptied of air, the salmon may get a reduced appetite, reduced feed utilization, increased fin wear and beginning dorsal deformation. To give salmon in a submerged cage access to air, the cage may be raised and lowered regularly. This may be problematic in long peri- ods of bad weather. Alternatively, an air bell may be positioned in the cage. The air bell is typically formed as a dome, wherein an upper portion of the dome is filled with air.

A prior-art air bell comprises a separate unit which is typically positioned at the centre of the cage. Because of the great buoyancy that an air bell may provide, the air bell requires a solid anchoring. For that reason, a prior-art air bell is not suitable for rais- ing and lowering together with a lowerable modern cage. Further, air bells have the substantial drawback of bringing many foreign elements into the cage, which is disad- vantageous for the fish swimming in the cage.

2 DK 2021 70018 A1 Patent document NO312873 B1 discloses a submersible cage including a vertical cen- tral pipe and a diamond-shaped enclosure.

The pipe is formed as a floating buoy.

By supplying water or air into the pipe, the cage may be raised and lowered in the water column.

Further, a lower portion of the enclosure may be adjusted vertically relative to — the buoy.

Patent document WO2016063040A1 discloses a polygonal submersible cage in which air-filled buoyancy floats keep the cage in a vertical position in the water column.

Patent document WO9624245A1 discloses a cage which can be submerged below the water surface.

The cage is provided with two floating rings that, via valves, can be filled completely or partially with air or water.

The cage is lowered by filling the rings with water, and the cage is raised by filling the rings with air.

The position of the cage in the submerged state is secured with floating buoys in the water surface.

Patent document 20001217 discloses a submersible fish-farming cage comprising a buoyancy element with a net bag and a bottom ring.

On the buoyancy element, sev- eral wires are arranged, including buoyancy elements which are also attached to the vertical walls of the net bag.

The bottom ring is slidingly arranged on the wires and is vertically displaceable in the water column so that the volume of the net bag may be changed.

The invention has for its object to remedy or to reduce at least one of the drawbacks of the prior art or at least provide a useful alternative to the prior art.

The object is achieved through the features that are specified in the description below and in the claims that follow.

General description of the invention The invention is defined by the independent claims.

The dependent claims define ad- vantageous embodiments of the invention.

In a first aspect, the invention relates more specifically to a fish-farming cage, the fish-farming cage comprising a first buoyancy element with a first diameter, a second buoyancy element with a second diameter, a third buoyancy element with a third di- ameter, a closed enclosure including a bottom wall and a top wall and an anchoring.

In a submerged position, the second buoyancy element is vertically displaceable in a wa- ter column relative to the first buoyancy element when the first buoyancy element is positioned in a water surface, and the first buoyancy element includes a first work

2 DK 2021 70018 A1 platform and the second buoyancy element includes a second work platform. The fish-farming cage described herein may form a shape like a double cone when the second and third buoyancy elements have been submerged in the water column. A portion of the enclosure may be a net. A portion of the enclosure may be a tarpaulin.

— An effect of the second buoyancy element in a submerged position being vertically displaceable relative to the first buoyancy element is that the fish may be crowded without the use of a separate net. Crowding of the fish takes place, for example, when the fish are to be treated for lice or disease, or when the fish are to be slaughtered. According to the prior art, crowding of the fish may take place by arranging a crowd- ing net on the inside of the enclosure, after which the net is pulled towards the water surface and/or towards one side of the enclosure so that the fish are gathered in a smaller volume of the cage.

Another effect is that the volume of the closed enclosure can be adjusted. When the fish are small, the second buoyancy element may be raised in the water column to- wards the first buoyancy element to give the enclosure a reduced volume adjusted to the biomass of the fish. As the fish grow, the second buoyancy element can be sub- merged relative to the first buoyancy element to give the enclosure a larger volume adjusted to the biomass of the fish.

The effect of the first buoyancy element including a first work platform is that a crew has access to the fish-farming cage and can inspect and operate the fish-farming cage as is known in the art, when the first buoyancy element is floating in the water sur- face.

The effect of the second buoyancy element including a second work platform is that a crew has access to the second buoyancy element when the second buoyancy element is floating in the water surface.

By the first and second buoyancy elements including work platforms, the work plat- forms may always be accessible when one or both of said buoyancy elements are floating in the water surface. The fish-farming cage may include more than three float- ing elements.

— The first buoyancy element and the second buoyancy element may be arranged to float in the same plane in the water column.

The first and second buoyancy elements may be arranged to float in the same plane,

. DK 2021 70018 A1 as the second diameter of the second buoyancy element is larger than the first diame- ter of the first buoyancy element, the second buoyancy element thereby being able to surround the first buoyancy element.

The effect of the first and second buoyancy elements possibly being arranged to float in the same plane is that a vessel may come alongside an outer portion of the cage, more particularly alongside a portion of the second buoyancy element, without the risk of the vessel damaging the enclosure. When the first and second buoyancy elements are floating in the same plane, the top wall of the enclosure will typically be arranged in the water column between the first floating element and the second floating ele- ment. At least one of the buoyancy elements includes a projecting portion arranged to form a vessel-receiving element. The effect of the projecting portion is that a vessel, for example a workboat or a well- boat, may come alongside the cage with a reduced risk or no risk of damaging the cage, and especially the enclosure. The projecting portion may be formed as a quay. The projecting portion may extend at a distance from the buoyancy element so that a safety distance is created between the enclosure and the vessel. The projecting por- tion may include a surface arranged to be a work platform. The projecting portion may be arranged on the first buoyancy element. The projecting portion may be arranged on the second buoyancy element. When the first buoyancy element is floating in the water surface and the second buoy- ancy element has been submerged, the top wall may form a truncated conical shape that extends slopingly from the first buoyancy element outwards and downwards to the second buoyancy element. A vessel which is to come alongside the first buoyancy element may thereby have to pass over a portion of the top wall. Such a passing in- volves the risk of a portion of the vessel, for example a propeller, possibly coming into contact with the top wall so that the net is damaged. This problem may be solved by arranging a projecting portion on the first buoyancy element as described herein. A projecting portion arranged on the first buoyancy element may have a length which substantially corresponds to the difference in radius between the first buoyancy ele- ment and the second buoyancy element. When the first and second buoyancy ele- ments are in the same plane, the projecting portion may form a platform between the first and second buoyancy elements. A walkway may extend from the first buoyancy element to the second buoyancy ele-

; DK 2021 70018 A1 ment. The effect of a walkway possibly extending from the first buoyancy element to the second buoyancy element is that a person may move between the first and the second buoyancy elements when the first and the second buoyancy elements are floating in — the water surface. In a first end portion, the walkway may be attached to the first buoyancy element. In a second end portion, the walkway may be attached to the second buoyancy element. The attachments may be flexible, so that the walkway may follow the movements of the buoyancy elements.

The fish-farming cage may include a plurality of walkways. Thereby a movement of crew and equipment between the first buoyancy element and the second buoyancy element may be simplified.

The walkway may be telescopic. The effect of a telescopic walkway is that the walkway may be attached to the first buoyancy element and the second buoyancy element in- dependently of the relative positions of the first and the second buoyancy elements. When the first buoyancy element and the second buoyancy element are floating in the water surface, the walkway may form a substantially horizontal position. When the second buoyancy element is submerged in the water column, a telescopic walkway may be extended and form a sloping position in the water column.

— The walkway may form a holding structure between the first buoyancy element and the second buoyancy element, wherein the holding structure is arranged to keep the first buoyancy element and the second buoyancy element in concentric positions.

In a submerged position, the third buoyancy element may be vertically displaceable relative to the second buoyancy element in the water column.

The effect of the third buoyancy element in a submerged position being vertically dis- placeable relative to the second buoyancy element is that a portion of the cage corre- sponding to the volume within the bottom wall can be crowded without the use of a separate net.

By displacing the second buoyancy element and the third buoyancy element relative to each other and relative to the first buoyancy element, the entire cage can be crowded without the use of a separate net.

Like with the second buoyancy element, a movement of the third buoyancy element

_ DK 2021 70018 A1 can also be used to restrict the volume of the closed enclosure. The first buoyancy element and the second buoyancy element and the third buoyancy element may be arranged to float in the same plane in the water column. The effect of the first, the second and the third buoyancy elements’ being arranged to float in the same plane in the water column, for example in the water surface, is that the enclosure may be arranged to form an approximately flat shape, the flat shape being able to crowd all the fish in the fish-farming cage. A further advantage is that all the three buoyancy elements may be inspected from the water surface.

When the three buoyancy elements are floating in the same plane, the second buoy- ancy element will surround the first buoyancy element, and the first buoyancy element will surround the third buoyancy element.

When the three buoyancy elements are positioned in operative positions in the water column, the cage may form a diamond shape, in which the bottom wall and the top wall form an angle between themselves. This shape creates a large volume in an up- per portion of the cage, where the fish will typically stay and be swimming in a shoal. The angle between the bottom wall and the top wall gives good flow characteristics of the water, as the flow of water may more easily pass a diamond-shaped cage as de- scribed herein than a cage with a cylinder-shaped net. By the second floating element being arranged in an upper portion of the cage, the upper portion of the cage becomes more dimensionally stable than the cage with the cylinder-shaped net.

In addition, a relatively small vertical distance between the first and second buoyancy elements contributes to good dimensional stability. This is particularly important near the water surface, where the flow rate is greatest.

— The third buoyancy element may comprise a conically shaped bottom cap which may be provided with buoyancy rings.

The effect of the conically shaped bottom cap is that a lower end portion of the bottom wall can have a rigid and good tightening. The bottom wall may be formed as a coned net. A conically shaped bottom cap is suitable for collecting dead fish, faecal matter and uneaten feed in the enclosure. The conically shaped bottom cap may include a funnel for the dead fish, the faecal matter and the uneaten feed.

2 DK 2021 70018 A1 The funnel may include a shield or a barrier with slats arranged to prevent dead fish and waste from floating up from the bottom cap.

The bottom cap may include an out- let for the dead fish and the waste.

The third buoyancy element may include an attachment portion for an anchoring, the anchoring being arranged to position at least one buoyancy element in the water col- umn.

The effect of the third buoyancy element comprising an attachment for an anchoring is that a portion of the fish-farming cage can be submerged and raised in the water col- umn through one attachment portion, as the forces transmitted between the anchor- ing and the fish-farming cage may be distributed evenly from the third buoyancy ele- ment to the enclosure.

The fish-farming cage may be submersible.

By submersible may also be understood able to be pulled down.

By submersible may be understood that the fish-farming cage may be positioned below the water surface.

The fish-farming cage can be submerged and raised in the water column by adding or removing a ballast, or by the use of a winch.

When the cage is positioned below the water surface, the cage may be referred to as lowered, pulled-down or submerged.

The effect of the fish-farming cage being submersible is that the cage may be sub- merged in the water column to a level which is below a level where salmon lice and other parasites stay, in order thereby to prevent damage from salmon lice.

Alterna- tively, the cage may be submerged to below a level below an upper layer in the water column where, potentially, waves with a damage potential occur when there is bad weather and rough seas.

Another effect of submerge the cage in the water column is that a vessel or a piece of flotsam may pass over the cage without there being a risk of harmful interaction.

For example, a fish-farming facility that consists of a plurality of cages may submerge one or more cages to facilitate the access for a wellboat that is to come alongside a cage.

By the fish-farming cage being anchored via the third buoyancy element, a portion of the fish-farming cage or the entire fish-farming cage may be positioned vertically in the water column via just one attachment portion.

A portion of a shape element belonging to at least one buoyancy element may be per- forated.

; DK 2021 70018 A1 By a shape element may be understood an element arranged to give the buoyancy element a shape, for example a circular shape. The shape element may be a prior-art, endless round plastic pipe, typically used as a buoyancy element in a floating ring be- longing to a floating cage. A prior-art floating ring typically comprises two pipes func- tioning as buoyancy elements. The pipes may be closed. A portion of the pipes may be filled with a buoyancy material, for example a gas-filled synthetic material, for exam- ple expanded polystyrene. The primary function of the second buoyancy element is to keep a middle portion of the enclosure stretched so that the enclosure does not collapse. The secondary func- tion of the buoyancy element is to be a base for the second work platform when the second buoyancy element is floating in the water surface. In addition, the second buoyancy element is arranged to carry a certain weight of the enclosure. In the main, the buoyancy element includes pipes and components that are formed from polyeth- ylene (HDPE). Polyethylene has a specific weight of between 0.91 and 0.96, thereby being buoyant.

The effect of perforating a portion of the shape element is that the shape element may be filled with water so that the buoyancy forces in the buoyancy element are reduced, whereby the buoyancy element provides approximately neutral buoyancy or limited buoyancy.

A submersible fish-farming cage may advantageously have less buoyancy than a float- ing fish-farming cage which is always to be floating in the water surface. Thereby, the buoyancy forces to which the cage is subjected when the cage is positioned in the wa- ter column may be reduced. The buoyancy forces may include tension in the enclosure and forces to which the buoyancy element is subjected.

Calculations carried out by the applicant show that a second buoyancy element with too much buoyancy may experience vertical collapse, as the buoyancy will cause the buoyancy element to seek upwards in the water column. A submerged buoyancy ele- ment will, to a great extent, move with currents in the water and thereby be subjected to alternating forces from the enclosure and the water. If a portion of the second buoyancy element receives a deviating load, a shape element with high buoyancy be- longing to the buoyancy element may become deformed and collapse.

The applicant's calculations further show that sufficient buoyancy in the second buoy- ancy element may be provided with an endless pipe having a smaller cross section than the shape element. By perforating a portion of the larger shape elements and

1 DK 2021 70018 A1 providing the buoyancy elements with one or more smaller pipes to provide buoyancy, the buoyancy may be optimized and adjusted according to the real requirements, and the risk of vertical collapse may be eliminated.

The shape element may include a plu- rality of bulkheads dividing the shape element into several chambers.

One or more chambers may be filled with water via a perforation in the bulkhead.

In a second aspect, the invention relates to a method for moving a fish-farming cage according to the first aspect of the invention along a water surface, the method includ- ing the step of: a) arranging the first buoyancy element, the second buoyancy element and the third buoyancy element in the same plane.

The effect of arranging the fish-farming cage in the way described herein is that the cage may be assembled on shore and moved as an unified unit as the flat shape con- stitutes a limited transport volume of the cage.

The method may further include the steps of: b) positioning the flat cage in a water surface; ¢) arranging a moving device on the flat cage and on a moving vessel; and d) moving the flat cage by means of the moving vessel from a first location to a second location.

The effect of positioning the cage in the water surface and moving it from a first loca- tion to a second location, as described herein, is that the cage can be towed or pushed along the water surface also in shallow water.

The method may further include the steps of: e) arranging a flat cage on a vessel; f) moving the flat cage from a first location to a second location by the vessel; and g) arranging the flat cage on the water surface.

The effect of arranging a flat-packed cage on a vessel is that the cage may be moved over a longer distance in a controlled way to prevent the cage from being subjected to unnecessary loads from waves and rough sea while being moved.

1 DK 2021 70018 A1 The method may further include the steps of: h) arranging a first flat cage on a vessel; i) arranging a second flat cage over the first flat-packed cage; j) moving the first and second flat cages from a first location to a second location by the vessel; and k) arranging the second and first flat cages on the water surface. The effect of arranging a first cage and a second cage on the vessel, as described herein, is that the vessel may move more than one cage at a time. By enabling the cage to be arranged flat, also referred to as flat-packed, a plurality of cages may be stacked on top of each other.

In a third aspect, the invention relates to a method for crowding fish in a fish-farming cage according to the first aspect of the invention, the method comprising the steps of: i.) positioning the first buoyancy element in a water surface; ii.) carrying out a first lengthening of an anchoring between the third buoyancy el- ement and a seabed until the second buoyancy element is floating in the water column; and iii.) carrying out a second lengthening of the anchoring until the third buoyancy el- ement is floating in the water column.

— The effect of crowding the fish in the way described herein is that the fish may be crowded without the use of a separate crowding net.

Crowding fish according to prior-art may be done by the cage being emptied of weights, ropes and other equipment, and by a possible bird net being removed. Then the bottom ring of the cage is lifted by means of a work boat. The lifting may be very laborious, depending on the type of cage and the type of mooring. When the bottom ring has been lifted, the enclosure is lifted so that the volume of the cage below the waterline is reduced and the fish are gathered in a limited portion of the cage. Alterna- tively, the crowding may be done with a net. An external net is arranged in the cage and pulled around the fish by means of a work vessel being alongside. When the net surrounds the fish, the net is pursed in such a way that the fish are crowded in a lim-

i. DK 2021 70018 A1 ited portion of the cage. At the same time as the fish are being crowded, the fish are pumped over to a wellboat via a pumping pipe. It is known that prior-art crowding techniques may stress the fish, and that fish may die.

By crowding the fish in the way described by the invention, the crowding may be done in a simpler and gentler way. The method for crowding fish according to the invention will give less stress, fewer injuries and a reduced mortality rate for the fish.

In what follows, examples of preferred embodiments are described, which are visual- ized in the accompanying drawings, in which: Figure 1 shows a schematic top view of a fish-farming cage according to the in- vention; Figure 2 shows a schematic sectional drawing of the fish-farming cage; Figures 3a-d show, on a smaller scale, the fish-farming cage in different positions in the water column; Figure 4 shows, on a larger scale, the fish-farming cage flat-packed and floating in the water surface; Figure 5 shows a sectional drawing, on a larger scale, of the first buoyancy ele- ment; and Figure 6 shows a sectional drawing of the second buoyancy element.

Figure 1 shows a fish-farming cage 1 seen from above. The fish-farming cage 1 com- prises a first buoyancy element 10 with a first diameter D10, a second buoyancy ele- ment 20 with a second diameter D20, a third buoyancy element 30 with a third diame- ter D30, a closed enclosure 40 comprising a bottom wall 41 and a top wall 42, and an anchoring 50 comprising a winch 52 (shown in figure 2) and a wire 51. The buoyancy elements 10, 20, 30 have positive buoyancy. The wire 51 is attached, at its first end portion, to the third buoyancy element 30 and is attached, at its second end portion, to a winch 52 as shown in figure 2.

By letting the winch 52 pull the wire 51 in, at least one buoyancy element 10, 20, 30 may be pulled downwards in the water column. By letting the winch 52 pay out wire 51, at least one buoyancy element 10, 20, 30 may rise in the water column. A plurality of projecting portions 60, 60a are arranged to form a vessel-receiving ele-

DK 2021 70018 A1 ment. The projecting portion 60a is arranged on the first buoyancy element 10 and has a length that makes it possible for a vessel to come alongside the projecting por- tion 60a without getting into interaction with the top wall 42 when the second buoyan- cy element 20 has been lowered in the water column, as shown in figure 2.

Further, on the buoyancy element 20, a plurality of moorings 58 arranged, arranged to keep the fish-farming cage 1 in a horizontal position. A walkway 65 is arranged between the first buoyancy element 10 and the second buoyancy element 20. The walkway 65 is shown as a telescopic walkway 65. The first buoyancy element 10 comprises a first work platform 11, an inner shape el- ement 12 and an outer shape element 13. The second buoyancy element 20 compris- es a second work platform 21, an inner shape element 22 and an outer shape element

23. The shape elements 12, 13, 22, 23 are shown as endless plastic pipes. The first work platform 11 is arranged on top of and between the outer and inner shape elements 12, 13. The second work platform 21 is arranged on top of and between the outer and inner shape elements 22, 23. Figure 2 shows a simplified sectional drawing of the fish-farming cage 1 shown in fig- ure 1. It should be noted that in figure 2 some elements that are shown in figure 1 have been left out for the sake of illustration, while, at the same time, some other elements have been added. The first buoyancy element 10 is floating in a water surface 0. The second buoyancy element 20 and the third buoyancy element 30 have been pulled down in the water column by means of the winch 52, so that the enclosure 40 forms a diamond shape. The enclosure 40 is shown with a bottom wall 41, a top wall 42 and a roof net 43. The bottom wall 41 is shown with a double net, comprising an outer bottom net 413 and an inner purse seine 415, see below. The top wall 42 is shown with a double net, comprising an outer top-wall net 423 and an inner top-wall net 425. Further, on the first buoyancy element 10, a superstructure 15 is arranged, including a feeder 16 and a cage sensor 17.

The third buoyancy element 30 comprises a conical bottom cap 31 with a collecting tank 32 for waste and dead fish. A suction hose 33 arranged to suck the waste and the dead fish up to a receiving unit (not shown) above the water surface 0 is arranged

1 DK 2021 70018 A1 in the bottom cap 31. Figures 3a-d show the fish-farming cage 1 in different positions in the water column.

Figures 3a and 3b show the fish-farming cage 1 in a normal operative position.

A submerged position is shown in figure 3a and a partially submerged position is shown in figure 3b.

Figures 3a-3d show a sequence for how the fish may be crowded without the use of a crowding net.

If the fish-farming cage 1 is submerged (figure 3a), the fish-farming cage 1 is lifted so that the first buoyancy element 10 is floating in the water surface 0. Then the wire 51 is extended so that the second buoyancy element 20, because of its buoyancy, is floating in the water surface 0, as shown in figure 3c.

By a further exten- sion of the wire 51, as shown in figure 3d, the third buoyancy element 30 will rise in the water column because of its buoyancy, until the third buoyancy element is floating in the water surface 0. Figure 4 shows the fish-farming cage 1 floating in the water surface 0 in a flat shape, also referred to as flat-packed.

The top wall 41 and the bottom wall 42 have been tightened up to limit the depth of the fish-farming cage 1 below the water surface 0 as much as possible.

The superstructure 15 is not shown in figure 4. The fish-farming cage 1 may further be provided with an outer roof net 430 as shown in figure 2. The outer roof net 430 is not shown in figure 4. Figure 5 shows a cross section of the first buoyancy element 10, comprising an inner shape element 12, an outer shape element 13 and a floating element 14. Figure 6 shows a cross section of the second buoyancy element 20, comprising an inner shape element 22, an outer shape element 23 and two floating elements 14. A portion of the inner shape element 12, 22 and a portion of the outer shape element 13, 23 are arranged to be fillable with water, for example by a wall in the shape ele- ment 112, 13, 22, 23 being perforated.

The floating element 14 is arranged to provide buoyancy for the buoyancy elements 10, 20. The floating element 14 is arranged to be filed with a buoyancy means, for example air or a gas-filled synthetic material.

The first buoyancy element 10 and the second buoyancy element 20 further include work platforms 11, 21, superstructures 15 and a plurality of feed spreaders 16 as shown in figure 2. The superstructure 15 gives support for suspending the roof net 43 and the outer roof net 430.

i. DK 2021 70018 A1 The bottom wall 41 is shown reinforced with a relieving net 410, see detail in figure 2. The relieving net 410 is attached to the third buoyancy element 30 and is attached to the bottom wall 41 in a portion between the third buoyancy element 30 and the sec- ond buoyancy element 20.

As earlier mentioned, the bottom wall 41 is shown as a double net. The inner net 413 may constitute a portion of a purse seine 7. In a normal situation of operation, the lower portion 70 of the purse seine 7 is open so that dead fish, faecal matter and un- eaten feed can sink into the collecting tank 32. The lower portion 70 is closed by pull- ing on a pursing line 71 extending from the water surface 0 to the lower portion 70.

After that, the purse seine 7 is pulled upwards inside the fish-farming cage 1 by means of the pursing line 71 so that the fish in the fish-farming cage 1 are crowded upwards in the water column.

It should be noted that all the above-mentioned embodiments illustrate the invention, but do not limit it, and persons skilled in the art may construct many alternative em- bodiments without departing from the scope of the attached claims. In the claims, reference numbers in brackets are not to be regarded as restrictive.

The use of the verb "to comprise" and its different forms does not exclude the pres- ence of elements or steps that are not mentioned in the claims. The indefinite article "a" or "an" before an element does not exclude the presence of several such elements.

— The fact that some features are indicated in mutually different dependent claims does not indicate that a combination of these features cannot be used with advantage. Exemplary embodiments are set out in the following items:

1. A fish-farming cage (1), the fish-farming cage (1) comprising: - a first buoyancy element (10) with a first diameter (D10); - a second buoyancy element (20) with a second diameter (D20); - a third buoyancy element (30) with a third diameter (D30); - a closed enclosure (40) comprising a bottom wall (41) and a top wall (42); and - an anchoring (50), characterized in that in a lowered position, the second buoyancy element (20) is vertically dis- placeable in a water column relative to the first buoyancy element (10) when the first buoyancy element (10) is positioned in a water surface (10),

Le DK 2021 70018 A1 the first buoyancy element (10) including a first work platform (11) and the second buoyancy element including a second work platform (21).

2. The fish-farming cage (1) according to item 1, wherein the first buoyancy el- ement (10) and the second buoyancy element (20) are arranged to float in the same plane in the water column.

3. The fish-farming cage (1) according to any one of the preceding items, wherein at least one of the buoyancy elements (10, 20) includes a projecting portion (60, 60a) arranged to form a vessel-receiving element.

4, The fish-farming cage (1) according to any one of the preceding items, wherein a walkway (65) extends from the first buoyancy element (10) to the second buoyancy element (20).

5. The fish-farming cage (1) according to any one of the preceding items, wherein, in a lowered position, the third buoyancy element (30) is vertically displaceable relative to the second buoyancy element (20) in the water col- umn.

6. The fish-farming cage (1) according to any one of the preceding items, wherein the first buoyancy element (10) and the second buoyancy element (20) and the third buoyancy element (30) are arranged to float in the same plane in the water column.

7. The fish-farming cage (1) according to any one of the preceding items, wherein the third buoyancy element (30) comprises a conically shaped bot- tom cap (31).

8. The fish-farming cage (1) according to any one of the preceding items, wherein the third buoyancy element includes an attachment (32) for the an- choring (50), the anchoring (50) being arranged to position at least one of the buoyancy elements (10, 20, 30) in the water column.

9. The fish-farming cage (1) according to any one of the preceding items, wherein the fish-farming cage (1) is lowerable.

10. The fish-farming cage (1) according to any one of the preceding items, wherein a portion of a shape element (12, 13) belonging to at least one buoyancy element (10, 20, 30) is perforated.

i. DK 2021 70018 A1

11. A method for moving a fish-farming cage (1) according to item 1 along a water surface (0), the method comprising the step of: a) arranging the first buoyancy element (10), the second buoyancy element (20) and the third buoyancy element (30) in the same plane, so that a flat- packed fish-farming cage (1) is formed.

12. The method for moving a flat-packed fish-farming cage (1) according to item 11, the method further including the steps of: b) positioning the flat-packed fish-farming cage (1) in a water surface (0); c) arranging a moving device on the flat-packed fish-farming cage (1) and on a moving vessel; and d) moving the flat-packed fish-farming cage (1) by means of the towing ves- sel from a first location to a second location.

13. The method for moving a flat-packed fish-farming cage (1) according to item 11, the method including the steps of: e) arranging a flat-packed fish-farming cage (1) on a vessel; f) moving the flat-packed fish-farming cage (1) from a first location to a second location by the vessel; and g) arranging the flat-packed fish-farming cage (1) on the water surface (0).

14. The method for moving a fish-farming cage according to item 13, wherein the method, after step e), further comprises the step of: i) arranging a second flat-packed fish-farming cage (1) over the first flat- packed fish-farming cage (1).

15. A method for crowding fish in a fish-farming cage (1) according to item 1, the method including the steps of: i) positioning the first buoyancy element (10) in a water surface (0);

Lo DK 2021 70018 A1 ii) carrying out a first lengthening of an anchoring (50, 51) between the third buoyancy element (30) and a seabed (99) until the second buoyancy ele- ment (20) is floating in the water column; and iii) carrying out a second lengthening of the anchoring (50, 51) until the third buoyancy element (30) is floating in the water column.

Claims

DK 2021 70018 A1 CLAIMS

1. A fish-farming cage (1), the fish-farming cage (1) comprising: - a first buoyancy element (10) with a first diameter (D10); - a second buoyancy element (20) with a second diameter (D20); - a third buoyancy element (30) with a third diameter (D30); - a closed enclosure (40) comprising a bottom wall (41), a top wall (42) and a roof net (43); and - an anchoring (50), characterized in that: - the fish-farming cage (1) is submersible; - the fish-farming cage (1) forms a diamond shape when the three buoyancy elements (10, 20, 30) are positioned in operative positions in a water column; and - in a lowered position, the second buoyancy element (20) is vertically displaceable in the water column relative to the first buoyancy element (10) when the first buoyancy element (10) is positioned in a water surface (10), the first buoyancy element (10) including a first work platform (11) and the second buoyancy element including a second work platform (21).

2. The fish-farming cage (1) according to claim 1, wherein the first buoyancy element (10) and the second buoyancy element (20) are arranged to float in the same plane in the water column.

3. The fish-farming cage (1) according to any one of the preceding claims, wherein at least one of the buoyancy elements (10, 20) includes a projecting portion (60, 60a) arranged to form a vessel-receiving element.

4, The fish-farming cage (1) according to any one of the preceding claims, wherein a walkway (65) extends from the first buoyancy element (10) to the second buoyancy element (20).

5. The fish-farming cage (1) according to any one of the preceding claims, wherein, in a lowered position, the third buoyancy element (30) is vertically displaceable relative to the second buoyancy element (20) in the water column.

6. The fish-farming cage (1) according to any one of the preceding claims, wherein the first buoyancy element (10) and the second buoyancy element

20 DK 2021 70018 A1 (20) and the third buoyancy element (30) are arranged to float in the same plane in the water column.

7. The fish-farming cage (1) according to any one of the preceding claims, wherein the third buoyancy element (30) comprises a conically shaped bottom cap (31).

8. The fish-farming cage (1) according to any one of the preceding claims, wherein the third buoyancy element includes an attachment (32) for the anchoring (50), the anchoring (50) being arranged to position at least one of the buoyancy elements (10, 20, 30) in the water column.

9. The fish-farming cage (1) according to any one of the preceding claims, wherein the fish-farming cage (1) is lowerable.

10. The fish-farming cage (1) according to any one of the preceding claims, wherein a portion of a shape element (12, 13) belonging to at least one buoyancy element (10, 20, 30) is perforated.

11. A method for moving a fish-farming cage (1) according to claim 1 along a water surface (0), the method comprising the step of: a) arranging the first buoyancy element (10), the second buoyancy element (20) and the third buoyancy element (30) in the same plane, so that a flat- packed fish-farming cage (1) is formed.

12. The method for moving a flat-packed fish-farming cage (1) according to claim 11, the method further including the steps of: b) positioning the flat-packed fish-farming cage (1) in a water surface (0); c) arranging a moving device on the flat-packed fish-farming cage (1) and on a moving vessel; and d) moving the flat-packed fish-farming cage (1) by means of the towing vessel from a first location to a second location.

13. The method for moving a flat-packed fish-farming cage (1) according to claim 11, the method including the steps of:

ot DK 2021 70018 A1 e) arranging a flat-packed fish-farming cage (1) on a vessel; f) moving the flat-packed fish-farming cage (1) from a first location to a second location by the vessel; and g) arranging the flat-packed fish-farming cage (1) on the water surface (0).

14. The method for moving a fish-farming cage according to claim 13, wherein the method, after step e), further comprises the step of: i) arranging a second flat-packed fish-farming cage (1) over the first flat- packed fish-farming cage (1).

15. A method for crowding fish in a fish-farming cage (1) according to claim 1, the method including the steps of: i) positioning the first buoyancy element (10) in a water surface (0); ii) carrying out a first lengthening of an anchoring (50, 51) between the third buoyancy element (30) and a seabed (99) until the second buoyancy element (20) is floating in the water column; and iii) carrying out a second lengthening of the anchoring (50, 51) until the third buoyancy element (30) is floating in the water column.