Clearly any activity has the potential to pollutebut the entire aquaculture profession is in favour of protecting the environment and improvements in Best Management Practice are continually worked upon at both the corporate and Association level.

The impact of farming on water quality through the discharge of nitrogen (N) and (P) and other materials (mainly, uneaten feed) has attracted attention from the public, pressure groups, ecologists and authorities involved in managing water resources.

Some years ago, the Scottish Environmental Protection Agency, SEPA, published estimates of compounds, containing Nitrogen, being discharged by salmon farms as 100 kg per ton of feed used. These figures are now out of date but continue to be widely quoted.

More accurate estimates are 32 kg N/ton salmon produced, with P at 7 kg/ton of salmon produced. Such levels are relatively minor in comparison with the N and P discharge to sea from human land-based activities and, of course, the natural cycle of life in the seas.

The company Nutreco has been involved in joint studies, for example in  Scotland, to investigate the impact of salmon farming activities. Information generated in these studies confirms that the levels of impact have decreased significantly throughout the 30-year history of modern fish farming and further reductions can be expected.

Studies, for example by the Scottish Marine Biological Association (now Scottish Association for Marine Science) and on behalf of the British Columbian Salmon Farmers Association (a two-year $600,000 study), have shown that the build up of waste from salmon farms is limited both in distance from the farm - less than a couple of hundred metres - and in the time it lasts, with the sea bed  able to return to its initial state within a few months.

As modern aquaculture continues to evolve, farm sites are increasingly being located further offshore where the depth of the water is higher. In these areas, the farming installations (floating and/or cages) are also exposed to greater levels of water movement and faster currents, providing faster dilution and of waste materials.

Measures of fauna and flora in the area around a salmon farm ( studies) are used by SEPA as part of their procedures when granting licences to marine farms.

Since the advent of modern salmon farming there have been substantial investments made in  research by corporate interests as well as R and D institutions. The development of more efficient feeds combined with improvements in feed management and in systems - using loops with, for example, underwater TV cameras and Doppler systems - have significantly reduced the amount of feed that remains uneaten. Minimising the uneaten feed is of ecological and economic interest to the farmer.

Modern feeds are highly digestible and fish convert these efficiently into meat. As a direct result, the fish produce relatively small amounts of faeces. Research actively continues to improve both the content and technology of feed manufacture to provide the optimum conditions for fish and health