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In-situ net cleaning system in aquaculture

Final Report Summary - NETWASH (In-situ net cleaning system in aquaculture)

Fishing intensification during the past resulted on increased pressure on wild fish stock and posed a risk on the marine ecosystems' balance. As such, the European Union aimed to revise the Common Fisheries Policy (CFP) so as to reduce exploitation of wild fish and promote resources' sustainable development. Aquaculture appeared as a viable alternative, ensuring supply of fish products while providing employment options in many fishing dependant regions in Europe.

Nevertheless, questions over pollution and eutrophication resulting from aquaculture activities arose, with net fouling consisting one of the major disturbances of the inshore industry. On the one hand, fouling clogged the meshes and impeded water passage through the cages, thus increasing the potential for disease, fish mortality and loss of stock. On the other hand, the necessary conventional net cleaning resulted in discharging polluting chemicals, such as copper oxides, in the effluent water. The most common nets' maintenance practice was in-situ washing by divers, which raised health and safety considerations, particularly in the case of deep nets use. It was therefore estimated that the practice would gradually become non-applicable, since cages tended to become deeper and larger as the sector evolved. As a result the necessity to develop remote control and monitoring capabilities of the cleaning procedure emerged.

The NETWASH project aimed to address all the above mentioned issues through the development of a cost-effective, easy to operate net cleaning device for use in fish farming which could be remotely operated without the use of divers. The proposal did not involve chemicals utilisation and contributed to the environmental and economic sustainability of the aquaculture sector.

The system consisted of a vehicle using thrusters for motion and a combination of brushes and water suction for the cleaning process. The latter collected fouling organisms from the fish farm and raised them above water surface, without generating turbidity due to residues. The device was also equipped with camera and illumination instruments for net inspection purposes.

A detailed examination of fouling species, alternative materials and loads applied on the device during cleaning was initially performed, for both cold and warm water environment. Fouling conditions were monitored through the installation of frames in selected areas. Moreover, a prototype high pressure (HP) net washer was designed, according to the specified requirements. The design of the cleaning mouth was revised and evaluated several times, so as to achieve the desirable efficiency. The equipment was then integrated in a housing device, bearing camera and lighting, which allowed for positioning of the washer in all possible angles. The potential to construct the prototype using plastic materials was also investigated, because of their buoyancy and reduced production price.

In addition, a device control system was designed to supervise the unit positioning and the cleaning progress. After system finalisation, it was decided that the nozzles and cleaning heads would be positioned underwater while all other instruments were placed above surface. Brush rotation speed was monitored using a digital pulse generator. A main unit was finally assembled, able to control the operation of all system components and cleaning parameters.

The fully integrated net cleaning prototype was validated in terms of fulfilling its industrial objectives. It should be noted though that the ability of positioning during cleaning was not incorporated in the evaluated structure and remained a domain for post-project development. The initial device was revised after incorporation of the in-situ remarks and the finalised version was very promising in terms of performance. Nevertheless further refinement was required prior to producing a marketable product.

Activities were also undertaken in order to promote the technology in the aquaculture industry and investigate commercialisation, patenting potential and socioeconomic impacts of the innovation. Moreover, an attempt to establish synergies with academia was made. Finally, the acquired knowledge was disseminated in the general public through presentation in conferences, organisation of workshops, distribution of relevant documentation, communication with enterprises operating in the field and development of a project related website to inform all involved parts on the NETWASH proposal.

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