Discharges of nutrients from fish farming, together with discharges of waste water from households, industry and agriculture, affect environmental conditions in fjords and coastal waters. Fish farming results in discharges of excess feed and fish excrement. A great deal of effort has been put into improving feed and feeding routines, but total fish production has increased so much that discharges are still rising. Monitoring routines are established to make it possible to follow changes in environmental conditions and respond before recipients are damaged by pollution.
Fish farming can contribute to eutrophication
Discharges from fish farms contain the same types of nutrients and organic matter as domestic waste water and discharges from agriculture and certain types of industry, and they have the same impact on environmental conditions in fjords and coastal waters. A small fish farm, producing perhaps 500 tonnes of salmon a year, discharges about the same amount of nutrients as a town of 5 000 to 7 500 people.
Discharges from fish farms have most impact locally, in the immediate vicinity of each facility. If there are several fish farms in a fjord, their overall discharges may cause eutrophication. This is not currently a problem in Norway, but there are indications that problems may arise in certain fjords.
Risk of pollution near fish farms
Fish farms have often had a marked effect on the marine environment in their immediate vicinity. In the worst cases, discharges have caused the sediments and water under a fish farm to "rot".
Fish only thrive where the water quality is good, and grow poorly and become less resistant to disease in polluted localities. Polluted sites therefore have to be abandoned and the fish farms moved. This used to be a major problem both in environmental terms and for the fish farmers themselves.
Now that the risks are understood, the industry and the authorities are focusing on the development of sustainable fish farming that can be continued indefinitely at the same locations. However, further expansion of the industry may increase the risk of eutrophication in recipients used by several fish farms.
A rapidly growing industry
Fish farming started in the seventies. It is a rapidly growing industry: production of salmon and trout has risen from about 50 000 tonnes in 1985 to about 640 824 tonnes sold in 2005.
The fisheries authorities are managing the development of fish farming to ensure that it is a profitable and flourishing means of livelihood in coastal districts. Restrictions have been introduced on the number of licences that are issued. Fish farmers themselves are of course interested in producing as much fish as possible at the lowest possible cost. More effective production also benefits the environment, and discharges from fish farms have not been rising at the same rate as production.
Better feed quality, feeding routines and monitoring
Discharges per tonne of fish produced have been halved in the last 15 years with the introduction of better quality feed and improved feeding routines. In addition, the environment around fish farms is being more closely monitored, so that any environmental impact can be followed and measures to reduce discharges can be introduced before the environment is damaged.