RobustNot. Levetid til nøter i lakseoppdrett: Dokumentasjon av slitasje og aldring for utvikling av robuste oppdrettsnøter.

The main goal of this project is to establish knowledge, test methods and guidelines for development of robust net cages. This will contribute to increased sustainability in aquaculture through reduced escape of fish and extended lifetime of net cages. The project produces important new knowledge about factors that affect lifetime and strength of nets in fish cages for aquaculture. The lifetime of nets depends on several factors including physical, chemical and biological strains from the environment, netting material and coating, and how the net is handled. These factors have been identified by manufacturers and users of nets, but have been subjected to limited scientific studies and documentation. Based on research activities in the project and know-how provided by the industry partners, new test methods and test procedures are developed to assess and document properties of netting subjected to various forms of wear and deterioration that occur during operation. There is a special focus on contact wear, wear during washing of nets and damages due to wrong and accidental use of chemicals for disinfection. Emphasis is kept on developing objective measurement and test methods for netting, to establish a basis for industry standards and provide input to future revisions of national and international technical standards. This includes the ongoing revision of NS9415, where this project has provided improvements. The project has led to the creation of a consortium of companies, which work together to solve common R & D challenges for promoting innovation in the development of aquaculture nets. This consortium includes manufacturers of fish nets in the Norwegian aquaculture industry and research environments with leading expertise within the relevant topics. Results from the project indicate that the main causes of deterioration and damage to the net are structural changes in the netting (shrinkage) and wear from contact with equipment such as chain components, cage collars, high pressure cleaning equipment and other equipment. The project has developed specifications for wear resistance testing equipment to provide tools for development of improved products. The project has investigated whether the nylon fibers (polyamide 6, PA6), which netting is built up by, may contribute to observed reduction in strength in used nets. Investigations of netting with 50% measured decrease in mesh strength showed that tensile strength of polyamide fibers in the netting did not show the same degree of strength reduction. In addition, the fibers were examined chemically. This investigation showed that the fibers have a microstructure that is very similar to new fibers. This support findings that indicate that strength reduction in used nets is mainly due to structural changes in the netting and not due to deterioration of nylon fibres. A scientific paper published at the OMAE2017 conference in June 2017 presents a study of traditional netting materials subjected to disinfecting chemicals during fish farming and treatment of net cages. A series of tests were performed in order to study the short term effect of various concentrations of disinfecting chemicals on the tensile strength of Raschel knitted Nylon netting materials. Simulated spill of diluted hydrogen peroxide to the jump fence during de-lousing did not affect the strength of new and used knotless nylon netting samples. Below the water surface hydrogen peroxide reacted with biofouling forming gas bubbles, but this did not result in reduced netting strength. As expected, the performed tests did not indicate any effect on netting strength from a simulated single, traditional bath disinfection performed at service stations applying the disinfectant Aqua Des containing peracetic acid. However, increasing the Aqua Des concentration from 1 to 10 % resulted in a strength reduction of 3-6 %. Simulated spill of concentrated Aqua Des on the jump fence of a net with copper coating residuals resulted in a severe reduction in strength of 45 %. This strength loss was probably a consequence of chemical reaction between copper and Aqua Des, and uncoated netting did not experience any loss in strength subjected to the same chemical exposure. These findings from application of Aqua Des should also apply to other peracetic acid disinfection chemicals with trade names as for example Perfectoxid and Addi Aqua. The project has also identified and addressed challenges relating to definitions and measurement of dimensions of netting used in fish cages, including mesh size, twine thickness and solidity. It was concluded that there is a need to develop objective measuring methods, and the project aim to define measurement equipment based on image processing.

The project will produce important new knowledge about factors that affect the lifetime and strength of nets in fish cages for aquaculture. The lifetime of nets depends on several factors including chemical, biological and physical strains from the environment, raw material properties and how the net is handled. These factors have been identified by manufacturers and users of nets, but have been subjected to limited scientific studies and documentation. Based on research activities in the project and know-how provided by the industry partners, new test methods and test procedures will be developed to assess and document mechanical properties of netting subjected to various forms of wear and deterioration that occur during operation. There will be a special focus on contact wear, wear during washing of nets and aging as a result of chemical use. These are issues of particular interest in relation to damages found on nets used in fish aquaculture. Emphasis will be kept on developing objective measurement and test methods for netting, to establish a basis for industry standards and provide input to future revisions of national and international technical standards. The project will lead to the creation of a consortium of companies, which will work together to solve common R & D challenges for promoting innovation in the development of aquaculture nets. This consortium will include manufacturers of fish nets in the Norwegian aquaculture industry and relevant research environments. The results will stimulate innovation through the development of more robust and secure net cages and by providing advice on how nets should be treated, for example during removal of bio-fouling and parasites. More robust nets will have improved resistance against deterioration from wear and aging, and will thus better maintain strength and other mechanical properties in operation. This will help to reduce escapes of farmed fish and ensure more efficient use of resources.