Installations in the sea will always be exposed to fouling by shells and algae. Impregnation with copper is used to reduce this effect. Other reasons to impregnate with copper are to make the closing net stiff, prevent UV-radiation and to reduce the space between the filaments.
Pollution through toxic and harmful substances
Seep out of copper from closing nets and emission of copper from net laundries constitute the most significant contribution of toxic substances from the fish farm industry to the marine environment. About 80 per cent of the copper dissolve while the closing net is in the sea.
Over the last years the development has focused on alternative methods to prevent fouling. From 2004 the net laundries are obliged to clean the discharged water. An increasing number of fish farms also use mechanical methods like flushing and drying in stead of net laundries. The authorities will in cooperation with the industry also continue to strengthen the work to reduce use of chemicals in fish farming.
Use of medicaments to combat diseases
Different types of parasites may cause significant health damage for both farmed and wild fish. Medicaments that are used to combat salmon lice in fish farms are potentially damaging for organisms and animals in the water and in the sea bed around the net cages. The different medicaments have different environmental effects, but they all have in common that they may be toxic for many species. The extent of impact is however limited to a smaller area around the fish farm. The medicaments are decomposable, but the degrading process is slow.
To ensure that the combat of diseases and parasites within the fish farming industry is as environmentally friendly as possible, the authorities are attaching importance to developing alternative methods. There is an ongoing process to look for preventive health measures through new routines, and strategies for vaccination. The use of cleaner fish against sea lice in commercial aquaculture is an excellent example. The use of chemicals and medicaments are constantly being reduced in the fish farming industry.
Discharge of nutrient salts – a matter of localisation
Since the early 1990s there has been an increase in discharge of nutrient salts like nitrogen and phosphor, and organic material from the fish farming industry. The discharge come from dead fish, waste from fish meal and excrements, and can lead to fertilization in the mass of water. If the discharge exceeds the limit the water mass can tolerate, the quality of the water will be reduced.
The discharge of nutrient salts and organic material from aquaculture does in general not represent any environmental problem if looking at the individual enterprises at present. This is due to a location of such enterprises so that aquaculture is carried out in more exposed localities than earlier and in areas with better biological recipient conditions, high bearing capacity and generally good self-cleaning properties. It is nevertheless well-known that intensive aquaculture may affect the seabed below installations as a result of the sedimentation of waste and the dispersion and decomposition rate not being high enough. The localisation of aquaculture at sites that are adapted to the environmental conditions is therefore important.
From 1 January 2005 a new system to delimitate licence for fish farming, has been induced. The earlier system was based on cubic meters in net cage but the new system instead uses maximal approved biomass of fish in farms. This new system of measure combined with inducement of environmental surveillance during assignment of licence and surveillance of management, will secure a more sustainable and environmentally friendly production. In 2006 it will be a secured field of activity to elaborate further together with the development of good systems for determination of the environmental carrying capacity in the aquaculture industry.