FR3062025A1 - SUBMARINE BARRIER FOR THE PROTECTION OF SHELLFISH ON CUTTING CONCESSIONS OF PREDATION BY DAURADES - Google Patents

Abstract

The invention relates to a device for dissuading sea bream to come to eat shells in breeding on shellfish farms. It consists of a chain (1) of sufficient weight to keep the device immersed on the bottom, and a juxtaposition of foam strips (2) fixed by one of their ends, or directly on the chain (1), either on the rope of floats of a net itself attached to the chain (1). In immersion, the foam strips (2) rise towards the surface under the effect of buoyancy, constituting a permanent underwater barrier even in the presence of drifting algae and strong currents. The device according to the invention is particularly intended for shellfish production sites subject to tides.

Description

Holder (s):

LE FAOU RONAN JOSEPH MARIE.

O Extension request (s):

© Agent (s): LE FAOU RONAN.

© UNDERWATER BARRIER FOR PROTECTING SHELLFISHING ON CONCHYLIC CONCESSIONS FOR PREDATION BY DAURADS.

FR 3 062 025 - A1 (57) The invention relates to a device making it possible to dissuade sea bream from eating shellfish in farming on shellfish concessions.

It consists of a chain (1) of sufficient weight to keep the device submerged on the bottom, and a juxtaposition of foam strips (2) fixed by one of their ends, either directly on the chain (1), either on the float rope with a net itself fixed on the chain (1).

In immersion, the strips of foam (2) rise towards the surface under the effect of Archimedes' thrust, constituting a permanent underwater barrier even in the presence of drifting algae and strong currents.

The device according to the invention is particularly intended for shellfish production sites subject to the tides.

The present invention relates to a device for protecting shellfish (oysters, mussels, cockles, clams, etc.) in farming on shellfish concessions from predation by sea bream (sparus aurata).

The phenomenon of predation of shellfish farming on shellfish concessions by sea bream has become particularly worrying in recent years, over a large part of the French coast. Currently, three types of protection are used or under development to respond to this problem: the confinement of shells in protective bags or cages, the installation of physical barriers such as nets around the perimeter of concessions, and finally the use of acoustic transmitters whose development is not yet satisfactory.

The present invention falls into the category of physical barriers placed on the periphery of concessions and whose aim is to dissuade sea bream from going to feed on shellfish farming on concessions.

To date, the physical barriers used are nets of variable height (1 to 4 meters), and of mesh of about 100 mm on a side. When their positioning is parallel to the axis of the current, these nets give excellent results, and their only source of fouling requiring, in the long term (several weeks), a cleaning intervention is natural fouling (it is this phenomenon combined with the need to disturb the circulation of water as little as possible on the concession which requires the use of the widest possible meshes). On the other hand, when they are not positioned parallel to the axis of the current, these nets have the major drawback of retaining the drifting algae which get caught in the meshes and, by accumulating over time, cause the tilt, then the complete coating of the net under the effect of the current. In the best of cases, frequent cleaning keeps their effectiveness at a sufficient level. In the worst case, the net sets in a few tens of minutes and is therefore totally ineffective.

The device according to the invention makes it possible to remedy this drawback either as a pure and simple replacement of the net, or as additional equipment to be installed on the net. It consists of two elements.

The first is a chain (1) whose size is to be chosen so that the complete device is kept on the ground thanks to the weight of the chain (1) (in practice choose a chain weight corresponding to approximately 1.5 times the lifting force exerted by the floating elements of the device). In the case of additional equipment to the net, this chain (1) is fixed to the weighted rope of the net.

The second is a set of foam strips (2) fixed by one of their ends either directly on the chain (1) or on the float rope of the net. In immersion, each strip of foam (2), held under water by the weight of the chain (1), rises to the surface under the effect of Archimedes' force. The whole thus constitutes an underwater barrier which does not disturb the circulation of water on the concession, and does not retain an accumulation of drifting algae. When the horizontal force exerted by algae and the current reaches a value sufficient to lay down a strap (2), the algae slide along the latter and continue on their way, letting the strap (2) return to its upright position and restore the barrier. .

The foam must consist of a large majority of closed cells, and present a good compromise between low density and capacity for re-expansion after stress so as to maintain its buoyancy over time and so that a simple passage through the links of the chain (1) or a knot with a half-key is enough to ensure a lasting mooring (the re-expansion effort of the foam at the level of the link or knot ensures blocking).

The strips (2) can be of any section, equivalent to a round section with a diameter varying from 5 to 15 mm in most situations, to be chosen according to the speed of the current over the area to be protected (the stronger the current, and the larger the section). Their length will vary most of the time from 1 to 2 meters depending on the bathymetry and the topography of the sites.

The distance between two neighboring strips (2) should ideally be between 10 and 20 cm, but may be different.

The accompanying drawings illustrate the invention:

Figure 1 shows an overview of the device alone in immersion.

Figure 2 shows an overview of the device as additional equipment on a submerged net.

FIG. 3 represents a detailed view of a method of fixing the straps on a chain.

With reference to these drawings, the installations used to validate the effectiveness of the present invention were carried out on concessions for the production of hulls on foreshore. They were made with a 10 mm galvanized chain (1), with a specific weight of 1.5 kg / m and foam strips (2) with a length of 1.2 m cut from tubes intended for use in swimming pools, called "Fries", having a cross section of equivalent diameter 12 mm.

The straps (2) were tied on the chain (1) or on the float rope of the net by means of a knot with a half-key. They were spaced 10 cm apart in the case of direct attachment to the chain (1), and 20 cm in the case of mooring on the net. In both cases, the upward force due to buoyancy is of the order of 0.1 Kg / strap (2).

The device according to the invention is particularly intended for shellfish production sites subject to the tides.

Claims (4)

1) Device to dissuade sea bream from eating shellfish in farming on shellfish concessions, characterized in that it consists in the upper part of a juxtaposition of strips of foam (2) vertical in 5 immersion, held on the bottom by a chain (1) of sufficient weight. 2) Device according to claim 1) characterized in that the straps (2) are closed cell foam of low density having the capacity to lose little volume after stress. 3) device according to claim 2) characterized in that the straps (2) are directly fixed on the chain (1) by simple passage through the links. 4) device according to claim 2) characterized in that the elements are fixed on an existing net, the chain (1) being moored on the weighted rope of the net and the straps (2) on the rope of floats of the net by a simple half-knot knot.