The present invention relates to a system to prevent fish from escaping a fish farm, according to the preamble of patent claim 1. Background

Since the beginning of fish farming, it has been a big problem that no system has been available to prevent fish from escaping upon damage to a farm. If there is a leak in a fish cage, the fish escaping will spread out fast and disappear in the area. This is unprofitable to the fish farming industry and a danger to the population of wild salmon.

A fish cage comprises generally a floating collar and a net fastened to the collar. Upon a hole in the net, the fish can swim freely into the ocean. A hole can be the result of many different actions, for instance may otter or seal bite a hole in order to get hold of fish, or weather and wind may tear a hole in the net. The net also gets fouled which is a disadvantage. If it is a relatively small hole, the hole might be there for a long time before the workers of the plant notice it. Before the net is repaired, a large amount of fish might have escaped. If the hole is large a lot of fish might escape even if the workers find the hole once they enter the farm.

Just as long as fish have escaped from the fish farms, different forms for catching them again have been tried. It has however, proven difficult to catch them without hurting them too much, as they should be transported back into the fishnet. I most cases they are not suited for humans to eat, because they are full of fodder pellet. In sum very few fish are caught after an escape.

From a political and/or environmentally point of view, it is desired to limit the escape of fish from fish farms because this fish is blending with wild fish, and causes large, maybe irreversible damages to the nature. The economy of a fish farm will, of course, also be considerably improved if escaping is avoided.

There have been attempts to limit escaping since the very beginning. One has tired to develop better nets, stronger nets, and to fasten these better to the floating collars in such a way that weather and ocean currents do not tear the nets. Double nets are also used for fish farming, as two nets are placed on the outside of each other, and if there is a hole on the inner net, the fish will flow out into the room between the nets. However, the distance between these nets are so small that if a fish stays there for a long time, it will be strongly injured. Further, there is no method to remove the fish captured between two nets, without removing the whole net. Object

The object of the present invention is to provide a system where escaping from a fish cage is limited or preferably totally prevented, and where the fish can be caught again, without injuries. A further object is that the invention should be easy to use and cost efficient in form of savings.

The invention

The present invention meets the objects with a system according to the characterising part of the independent patent claim. Further advantageous features are stated in the dependent claims. The invention is related to a system for preventing escape of farmed fish, as the system comprises an outer fencing surrounding a number of fish cages, at the least one. The outer fencing is performed with sidewalls, preferably of the same type of net as a traditional fish cage, in such a way that farmed fish being in a fish cage must pass two nets before coming into free water. The fencing should be considerably larger than the fish cage, so that fish being caught between the nets are not squeezed or hurt in any way. The sidewalls of the fencing should preferably be held upright by floating elements, and the fencing should anchored the same way as the fish cage. The fencing must also be washed, impregnated and maintained in the same was as the net of the fish cage.

The outer fencing is connected to at the least one assembling device, collecting fish coming into the device. The assembling device is preferably made of the same type of net as the fish cage, and is further embodied in such a way that fish entering it can not get out by it selves. Farmed fish recognizes the net wall, and will follow this as far as possible, and the outer fencing is connected to the assembling device in such a way that fish following the net wall will end up in the assembling device by them selves. Advantageously, the placement of the assembling device may be such that fish not following the net wall, but swimming towards the current, also will end up in the assembling device by them selves. In such a case the fencing may advantageously be connected to two opposite assembling devices.

In a particularly preferred embodiment, the assembling device is embodied as a traditionally fish trap. Preferably it is also performed with a system for emptying, in such a way that fish coming into the assembling device easily can be transferred to a new fish cage, towing bag, fish carrier boat or the similar, either for transferring back into the original fish cage, or for movement to a new location or for slaughtering.

As said above, farmed fish will follow the net wall as far as possible. Farmed fish will usually not go downwards unless it is affected by exterior conditions, and the outer fencing may thus be without bottom, because the fish will follow the wall and end up in the assembling device rather than going down and escape from the system. In the assembling device however, the density of fish can become unusually high, and the fish might get stressed when the assembling device is emptied. The assembling device should thus be performed with a bottom.

In a preferred embodiment of the system according to the invention, a closing is arranged in the transition between the outer fencing and the assembling device, wherein the opening between the outer fencing and the assembling device may be closed, so that fish no longer can get into the assembling device. This closing may be used when the assembling device should be emptied for fish, for instance when the fish should be transferred to another fish cage, to a fish carrier boat or the similar.

The outer fencing is floating due to floating units holding the net up, and in place by anchorings at the same way as a fish cage. Preferably it is used a different type of floating units than for a traditional fish cage. As mention above, otter and seal may bite a hole in the net in order to reach the fish in a fish cage. This may also happen to the net in the fencing, but it is less likely because fewer fish will be visible. To avoid the problem of predators as seal and otter ruining the net further, the floating units holding the fencing up may be performed in such a way that the animals easily can tilt themselves over. If they get into the fencing and bite a hole to the fish cage, the damage will be less as the fish only will get into the outer fencing.

Example

In the following the present invention will be described with a particularly preferred example, as a system is shown in the accompanied drawings, where

Figure 1 shows a part of a system according to the invention, from the side,

Figure 2 shows a system according to Figure 1, as the assembling device is emptying, and

Figure 3 shows details of the assembling device. Figure 1 shows a part of a fencing 1, according to the invention, as the fencing surrounds two fish cages 2 of regular size. In the shown embodiment, the fish cages are on a row, however, they might also be in other formations. The fencing 1 has sidewalls 3 and bottom 4, as the sidewalls are held upright by floating units 5. The fencing 1 is connected to an assembling device 6, and may be separated from this by a closing 7, in the transition between fencing 1 and assembling device 6, the closing is shown by broken lines in Figure 1. The details of the fencing, closing and the assembling device are shown in Figure 3.

Figure 2 shows how a preferred embodiment of the assembling device may be emptied. In one end of the assembling device 6, opposite to the end of the assembling device being attached to the fencing 1, it is provided with an outlet 8. Upon emptying a removable unit is connected to this, in the shown case it is a smaller fish cage 9. The closing 7 between the fencing 1 and the assembling device 6 is closed, and placed in a power block of a winch of a vessel, in Figure 2 shown as a boat 10, which is emptying the assembling device 6. The net is then elevated in such a way that it slopes towards the opening 8, and fish will thus flow over in fish cage 9. The boat 10 is moving forward, and the net is moving in the block, in such a way that the part of the assembling device 6 being between the boat 10 and the outlet 8 is becoming smaller and smaller. When the assembling device is sufficiently emptied, the net is removed from the power block, and the assembling device is being set up again.

Figure 3 shows a particularly preferred embodiment of the assembling device 6, having an outer part 11, an inner part 12, sidewalls 13, bottom 14 and leading walls 15. It is not shown any outlet of the assembling device 6 in Figure 3, and the shown parts of the fencing 1 are shown without fish cages. In the transition between the assembling device 6 and the fencing 1, the bottom 14 and sidewalls 13 of the assembling device 6 are performed with a purse line 7, and this functions as a closing. The purse line 7 may be pursed together, and for instance be placed in the power block of a winch on a vessel when the assembling device should be emptied.

In order to keep the assembling device 6 in form in the sea, at the same time as it is soft enough to pass through the power block of a winch, the shown embodiment is performed with a bar 16, preferably a metal bar, running across the inner part 14 of the device. This bar 16 is removed when the device 6 is emptied, but supports the device in such a way that it keeps the shape better during a long period of time. In the embodiment shown in the Figures, the bottom 14 of the assembling device 6 is shown shallower than the bottom 4 of the fencing 1. This is because it is easier to keep the shape of the assembling device 6 when it is shallower, but the depth of the assembling device does not affect the function of the system. To hold net in shape in sea may be solved in many ways, which will be obvious for a person skilled of the art, the solution comprising the bar as described herein, is thus just an example and should not be interpreted as limiting. The assembling device 6 is performed in such a way that the fish is automatically led into an inner part 12, without possibility to get out again. In the shown embodiment in Figure 3, this is achieved by use of to opposite leading walls 15 leading towards the inner part 12, at the same time as they incline towards the middle. These leading walls 15 are preferably made of the same type of net as the rest of the assembling device. At the bottom and along the edge facing a side wall 13 of the device, the leading walls 15 are sewn to the bottom 14 and to the adjacent sidewall of the assembling device 6, respectively. The leading walls 15 are further provided with plumb bobs 17 holding them vertically in the water. In the upper part the leading walls 15 are provided with floating units 18, and in the upper corners 19 facing the inner part of the assembling device 12, each wall 15 is fastened to the bar 16 stiffening the assembling device. The upper corners 19 are also fastened to a common oblong floating element (shown with broken lines in Figure 3 for a better understanding of the Figure). The fastening to the oblong floating element and to the bar 16 is performed in such a way that the leading walls 15 are forced apart in the upper part, so that a V-shaped passage are made between them. To further secure that an opening is kept between the walls, the vertical edges 20 of the leading walls 15 facing each other, and constituting the opening, are stiffened, for instance with an cord being sewn to the edge. Fish following the net wall will thus find this opening, and enter the inner part 12 of the assembling device, at the same time as the opening is so narrow that fish will not swim out through the same. The embodiment of the leading walls and the fastening of these to the assembling device may be performed in many ways, for instance as for a regular fish trap, which will be obvious to a person skilled of the art. The leading walls described above should thus not be interpreted as limiting to the invention as it is described in the following claims.