WO2018059674A1

WO2018059674A1 - A method for farming fish and an artificial barrier used for the method

Info

Publication number: WO2018059674A1
Application number: PCT/EP2016/073108
Authority: WO
Inventors: Helgi Larsen
Original assignee: Helgi Larsen
Priority date: 2016-09-28
Filing date: 2016-09-28
Publication date: 2018-04-05

Abstract

A method for farming fish (5) wherein the fish are kept in a desired volume of water. The method comprises the steps of selecting a volume of water delimited partially by natural barriers (2, 3, 4) to the fish (5) and providing an artificial barrier (6) for the fish (5) in the form of a virtual barrier of sound (10) adapted to provoke a response in the fish (5) and inhibiting them from passing the artificial barrier (6).

Description

A method for farming fish and an artificial barrier used for the method

The present invention relates to a method for farming fish and an arti- ficial barrier used in the method.

In recent year an increased focus on sustainability as well as marked demand for fish, such as salmon, for human consumption has lead to an increase in fish farming, in particular off-shore fish farming.

Currently, in off-shore fish farming the farmed fish are kept in large enclosures formed by nets. Typically such enclosures are large cylindrical basket-like nets with mesh sizes suitable for the size of fish as they grow. Though large, the nets will however still limit the possibility of the fish to swim. Accordingly, they move less around and get less exercised as compared to the situation in the wild. This gives a lower meat to fat ratio, and reduces the value of the fish, as costumers generally prefer fish with low fat.

Such nets are generally prone to damage from external factors such as storms, drifting objects, etc.

Fish in the enclosures are fed using slowly sinking fodder thrown in the water. Due to the high concentration of fish, the fish face an increased risk of diseases, infections, parasites etc. Consequently, medicine and other chemicals are also added to the water.

The high concentration of fish, fodder and excretions in one place leads to a high increase in nutrients in the water, in turn, leading to increased growth of plants and algae which accumulate on the net of the enclosures. This inter alia makes them even more prone to damage from storms and the like. Cleaning of the nets is therefore necessary, involving manpower and incurring costs.

On this background it is the object of the invention to provide a method and an enclosure for farming fish, not suffering from the above draw- backs.

According to a first aspect of the present invention, this object is achieved by a method for farming fish wherein the fish are kept in a desired volume of water, said method comprising the steps of selecting a volume of water delimited partially by natural barriers to the fish, providing an artificial barrier to the fish so as to enclose said volume, wherein said artificial barrier is a virtual barrier adapted to provoke a response in the fish inhibiting them from passing the barrier, e.g. by making them change their swimming direction.

By not having physical barriers such as nets, which are prone to destruction and pollution, the maintenance of the enclosures are highly reduced, and likewise the costs.

Likewise, the object is according to a second aspect of the invention solved by an artificial barrier for an enclosure for farming fish wherein the fish are kept in a desired volume of water within said enclosure, characterized in that said artificial barrier is a virtual barrier comprising means for provoking a response in the fish so as to inhibit the fish from passing the barrier.

According to a preferred embodiment of the first aspect of the invention, said virtual barrier comprises sound adapted to provoke said response in the fish. Sounds are easy to produce and propagate well in water. The barrier may therefore be easily established using appropriately placed acoustic emit- ters in the water.

According to a further preferred embodiment of the first aspect of the invention, wherein said natural barriers to the fish comprise the sea bed and the sea surface. Thus by simply placing the acoustic emitters side by side at the surface in a suitable configuration such as a polygon, a circle or other closed topology and directing the sound from them downwardly towards the seabed an enclosure for the fish may be formed.

According to a further preferred embodiment of the first aspect of the invention, said natural barriers to the fish comprise the sea bed, the sea shore and the sea surface. This allows the acoustic emitters to simply be arranged side by side along a line from shore to shore across a bay, a fjord or the like.

According to another preferred embodiment of the first aspect of the invention the sound is emitted downwardly from acoustic emitters located at the surface. Having the acoustic emitters at the surface allows easy access for maintenance, repair or the like.

According to yet another preferred embodiment of the first aspect of the invention, the sound comprises sounds in the range of 10 Hz to 50 kHz. Fish show good responses to sounds in this range, such as startle responses where fish change their swimming direction and turn away from the artificial barrier.

According to a preferred embodiment of the first aspect of the invention, the sounds are emitted over a sound spectrum. Using a sound spectrum, such as white or pink noise or a ping, a chirp or other frequency sweep allows responses to be provoked in a wide range of fish using one and the same virtual barrier. Evidently, however sounds may also be emitted as pure tones, be it as discrete tones or parts of frequency sweeps.

According to a further preferred embodiment of the first aspect of the invention the sound is emitted intermittently. This keeps power consumption down and reduces undesired noise pollution of the surrounding environment. Preferably, the sounds are emitted with a duty cycle in the range of 5-50%, preferably 10%, and a period of less than 1 second, preferably 0.5 second. It may however also be envisaged to use varying durations of and intervals be- tween the sound emissions so as to reduce habituation in the fish.

According to another preferred embodiment of the first aspect of the invention, a physical barrier is provided outside of said volume of water. An additional physical barrier is advantageous in the sense of redundancy. Not only will such a barrier prevent the fish from escaping, should the virtual bar- rier be breached or otherwise fail, e.g. due to interruption of the power supply, but it will also protect the fish against external predators, such as whales or other species of fish, which may have different responses than the captive fish. Preferably, said physical barrier comprises a net.

According to a further preferred embodiment, the sounds have fre- quencies and intensities adapted to killing sea lice. Sea lice, which is a problem in salmon farming, will then continuously be removed from the fish, whenever the fish approach the barrier.The present invention will now be de- scribed in greater detail based on non limiting exemplary embodiments of the invention and with reference to the drawing on which:

Fig. 1 shows an embodiment of enclosure used in the method of the invention.

In Fig. 1 a typical environment for the method for farming fish according to the invention is schematically shown. More specifically the environment is a coastal region such as a fjord or a bay. Natural landscape formations such as mountain slopes 1 lead down to shorelines 2. The mountain slopes 1 continue under the sea surface 3 and form the seabed 4. The sea surface 3, the shorelines 2 and the seabed 4 form natural barriers for fish 5 in the water.

To keep the fish 5 within a selected volume of water in order to farm them, the natural barriers are, however, insufficient as they do not delimit the water volume on all sides. Accordingly, an artificial barrier 6 according to the invention is provided. The artificial barrier 6 according to the present invention is a virtual barrier adapted to provoke a response in the fish inhibiting them from passing the barrier. Virtual in the following means a non-physical barrier, as opposed to physical barrier such as a net, a wall, or the above mentioned natural barriers such as the seabed 4 and interface to the atmosphere formed by sea surface 3. Instead the virtual barrier is a barrier in the sense that it provokes a reaction in the fish, preventing or inhibiting them from passing the barrier even though they could in principle pass it.

In the illustrated embodiment the artificial barrier 6 is an acoustic barrier. As can be seen a line or a cable 7 has been drawn from shoreline 2 to shoreline 2. The cable 7 is provided with floats 8 or similar buoyancy means to float in the surface. Integrated in the floats 8 or provided as separate units on the cable 7 are a number of acoustic emitters 9 adapted to emit sound 10 downwardly from the surface 3 where they acoustic emitters 9 float towards the seabed 4. For purpose of illustration the emitted sounds 10 are illustrated as waves in the left-hand side of the drawing only. Evidently, there will be sound waves emitted from all of the acoustic emitters along the cable 7 from shoreline 2 to shoreline 2 so as to have an unbroken artificial barrier 6 of sound from which the fish 5 will turn away due the sounds that provoke a re- sponse, e.g. the above mentioned startle response, scare response or flee response. The spacing between the individual emitters is evidently also so little than no gaps are provided. The actual spacing will depend on the directionality and the sound pressure produced by the acoustic emitters, the direc- tionality in turn also depending on the frequencies emitted. Higher frequencies allow higher directionality.

Rather than spanning from shoreline 2 to shoreline 2 the cable 7 could evidently also from a loop, i.e. a circle, polygon, or another closed topology floating on the sea surface 3 away from the shorelines 2, provided the distance to the seabed 4 is not too far.

In terms of distance it would also be possible to suspend the cable 7 in mid water and emitting sound both upwardly towards the sea surface 3 and downwardly towards the seabed 4, but for service reasons this is less preferred, as the cable 7 and the acoustic emitters 9 will be less accessible as compared to when they are floating on the sea surface 3. The same would apply to the option of letting the acoustic emitters 9 rest on the seabed 4 and emit upwardly.

The sounds emitted will depend on the species of fish to be kept in the enclosure. Generally sounds in the in the range of 10 Hz to 50 kHz will be suitable. Different species of fish 5, however, have different startle responses, and consequently depending on the species of fish 5 to be kept the emitted sounds may differ. The startle responses have e.g. been studied in "Startle response of captive North Sea fish species to underwater tones between 0.1 and 64 kHz.", Kastelein, Ronald A. et al, Marine Environmental Research 65, Vol. 2008, pages 369-377, Elsevier. URL: <http://www.sciencedirect.com/sci- ence/ article/pii/S0141 1 13608000056>. The sound may be a pure tone at a desired frequency, or it may cover a frequency range. If covering a frequency range, the sound may be a frequency sweep over the emission period e.g. a chirp or ping or it may be the simultaneous emission of all or several frequen- cies in the range, i.e. pink or white noise. The skilled person will understand that other possibilities and combinations exist. Following the study above, narrower ranges would be preferable in order to target the specific species of fish 5 kept and not spending power emitting sound at irrelevant frequencies.

Thus, it may be relevant to narrow down the frequency interval to 10 Hz - 4 kHz, to 10 Hz - 2 kHz, to 10 Hz - 400 Hz, to 10 Hz - 250 Hz, to 10 Hz - 70 Hz, or even to 40 Hz - 70 Hz, in order to include the ranges where fish 5 like Atlantic herring, horse mackerel, pollack, pout, thick lip mullet, sea bass and other species of fish 5 have their acoustic sensitivity or startle response. Atlantic herring appear to respond to pure tones at 4 kHz, and such pure tones could be used to target Atlantic herring rather than a frequency range. Adapting the acoustic emitters to these different sounds is merely a matter of programming of the electronic signal generator, and the signal processor of the signal generator may have several easily selected preset frequency ranges and/or emission modes. Each acoustic emitter may incorporate its own electronic signal generator or a central signal generator supplying all of the acoustic emitters may be used. Not all acoustic emitters need to emit the sounds concurrently, nor do they need to emit the same sounds or sound patterns. In addition to keeping the fish in, it should of course also be noted that the sounds may work as an artificial barrier 6 from either side, i.e. keeping predators such as whales and other species of fish out. Accordingly, the emitted sounds may also be targeted to this purpose.

The sounds need not be emitted continuously, but are preferably emitted intermittently in order to reduce power consumption and noise pollution of the environment. Preferably, sounds are emitted with a duty cycle in the range of 5-50%, preferably 10%, and a period of less than 1 second, preferably 0.5 second. However, the emission duration and pause need not follow a fixed cycle. Both the duration of the emission, the pause and the overall cycle time may be varied, e.g. randomly in order to avoid habituation, and potential diminishing of the response by the fish over time.

Furthermore, the frequencies and the intensities may be targeted towards other purposes, such as delicing of the fish from sea lice, Lepeophthei- rus salmonis, which poses a substantial problem in salmon farming. This the will delice the fish when they occasional approach the artificial barrier. This again may be done intermittently and randomly, so as to avoid the above- mentioned habituation. The frequencies selected could even be ultrasounds to which the fish do not respond, but which will kill the sea lice. Evidently, also additional sound transmitters may be placed a suitable locations within the selected volume of water. Similar, delicing using sound may also be used in other volumes of water in which fish are kept or transported, e.g. land based tanks or ponds.

Since, as will be understood from the above, the artificial barrier 6 is a virtual barrier, preferably based on electronically generated, emitted sounds 10, rather than a physical barrier. Should the virtual barrier be breached it will evidently be likely to have other causes for the breach than a physical barrier. Where, as explained above a physical barrier such as a net is prone to physical damage, from wind, weather and currents, as well as ships, large animals, and drifting object, the virtual barrier would be prone to other kinds of damage. Power failure would be one such risk, as offshore fish farming is of the located off the shores sparsely populated areas or islands, where the supply from power grid is less stable. Evidently, also failure of a signal generator or an acoustic emitter is a risk, which does not exist in the physical barrier.

For redundancy, it is therefore preferred to provide a supplementary a physical barrier, such as a net 1 1 is provided outside of said volume of wa- ter, so as to enclose both the desired volume of water in which the fish 5 are kept and the virtual barrier.

As can be seen in fig. 1 such a net 1 1 is suspended from shoreline 2 to shoreline 2. The net 1 1 is only represented schematically, and for illustration purposes only on the right-hand side of Fig. 1 . The net 1 1 is suspended from a cable or line 12 kept afloat by buoyancy members or floats 13, and reaches to the seabed 4. As can be seen in Fig. 1 , the net 1 1 is in the foreground of the landscape depicted. Behind the net 1 1 is the artificial barrier 6 provided by the virtual barrier made of sounds 10 emitted from the acoustic emitters 9 in Fig. 1 , so as to delimit the desired volume of water in the back- ground of the landscape, in which the fish 5 are kept. Should the virtual barrier be breached, the fish behind it will only be allowed to swim to the net 1 1 , where they would be stopped by the physical barrier provided by the net 1 1 . It should be noted that the net 1 1 is depicted only schematically, and evidently the mesh size will be selected to keep the fish 5 and possible predators out. A safety zone is thus created between the net 1 1 and the virtual barrier from which the fish 5 may be recovered when the artificial barrier 6 has been re- established after a breach.

Using the method and artificial barrier 6 according to the invention allows the easy and cheap establishment and maintenance of rather large enclosures for keeping fish 5. This in turn allows the fish 5 to swim freely, in turn increasing the quality as the freely swimming fish 5 will have a higher meat to fat ratio than fish 5 kept in traditional offshore enclosures, in turn allowing a higher sales price per kilogram of fish 5.

Claims

P A T E N T C L A I M S

1 . A method for farming fish wherein the fish are kept in a desired volume of water, said method comprising the steps of

selecting a volume of water delimited partially by natural barriers to the fish,

providing an artificial barrier to the fish so as to enclose said volume, wherein said artificial barrier is a virtual barrier adapted to provoke a response in the fish inhibiting them from passing the barrier.

2. A method according to claim 1 , wherein said virtual barrier com- prises sound adapted to provoke said response in the fish.

3. A method according to any one of the preceding claims, wherein said natural barriers to the fish comprise the sea bed and the sea surface.

4. A method according to claim 3, wherein said natural barriers to the fish comprise the sea bed, the sea shore and the sea surface.

5. A method according to any one of the preceding claims wherein the sound is emitted downwardly from acoustic emitters located at the surface.

6. A method according to any one of claims 2-5, wherein the sound comprises sounds in the frequency range of 10 Hz to 50 kHz.

7. A method according to claim 6, wherein sounds are emitted over a sound spectrum.

8. A method according to claim 6, wherein sounds are emitted as pure tones.

9. A method according to any one of claims 2 to 8, wherein the sound is emitted intermittently.

10. A method according to claim 9, wherein the sounds are emitted with a duty cycle in the range of 5-50%, preferably 10%, and a period of less than 1 second, preferably 0.5 second.

1 1 . A method according to any one of the preceding claims wherein a physical barrier is provided outside of said volume of water.

12. A method according to claims 1 1 , wherein said physical barrier comprises a net.

13. A method according to any one of claims 6 to 12, wherein the sounds have frequencies adapted to killing sea lice.

14. An artificial barrier for an enclosure for farming fish wherein the fish are kept in a desired volume of water within said enclosure,

characterized in that said artificial barrier is a virtual barrier comprising means for provoking a response in the fish in accordance with any one of claims 1 to 10 so as to inhibit the fish from passing the barrier.