Summary

Renholdelse af havbrugsnet

In this project, an alternative to the traditional copper based impregnation of marine aquaculture net cages has been investigated.

The method is based on a surface coating in combination with in situ cleaning of the nets when needed.

The nets are coated with a polymer (Net Coating) resulting in a smooth surface, which should prevent fouling of the nets – especially with mussels – and make it possible for divers to clean the nets in the water.

An environmental risk assessment of Net Coating was based on information from data bases on the individual substances in the product. The conclusion of the risk assessment is that Net Coating is not expected to give rise to unacceptable risks of environmental effects. However, information is lacking for a few substances and, this must be provided before a possible further use of Net Coating.

19 nets were coated before being allocated to five different stations, where they were situated during all of the 2008 season.

During the impregnation work at land, Net Coating and the traditional copper impregnation are equally easy to handle. The drying time needed for Net Coating is approximately as that for water based copper products, while copper products based on organic solvents have the advantage of allowing for positioning in the water before they are 100 % dry.

At present, Net Coating is approximately 6.00 NOK cheaper per litre than copper products. Furthermore, before use, Net Coating is mixed with water at a ratio of 1/1, which results in a total saving of approximately 14.00 NOK per litre. This saving could pay some of the possible extra costs for changing nets or having them cleaned by divers.

In conclusion, Net Coating is not an alternative to the traditional copper products in use. This conclusion is based on the experiences obtained during this project in combination with many years of experience at the fish farms and the diving company working with nets, change of nets and inspection of nets in the water. The results clearly show that Net Coating cannot meet the demands of the farms for the performance of impregnated nets.