Alternative Fish Cage Nets: Biofouling, Durability, Fish Growth

Summary:
Marine Harvest Canada tested the effectiveness of three alternative salmon cage nets for six months at a high current and wave area near Port Hardy, British Columbia. The three objectives of the testing were

1. to improve the environmental sustainability of salmon aquaculture by reducing the use of copper treated nets
2. to increase farm productivity by maximizing water flow, hence dissolved oxygen flow, through the net cages
3. to develop a proven system of cages and nets suitable for use in high current and wave offshore locations

Marine Harvest installed the best available offshore cages at a fully operational commercial salmon farm site at Shelter Bay in September 2010. With the AIMAP contribution of $196,000 two alternative nets that could meet the above objectives were purchased in November and June in 2010. The Dyneema and Thorn-D nets were tested in a controlled study using traditional nylon nets as the control. Monthly sampling generated data on biofouling community composition, biomass, and percent net occlusion. The nets were also evaluated for cost, fish growth, predator interaction, washing cost, handling, and physical performance.

This project provided the company with detailed information on the actual performance of nets that are marketed as being resistant to biofouling. The project compared the level of biofouling with the cost of the nets and treatments with the purpose of developing a program to ensure the best culture environment for the salmon at the best cost. The results showed that none of the materials tested performed well enough at preventing biofouling to meet the industry standards. This project was successful in proving that the net manufacturer’s claims for reduced biofouling (either inherent in the net material or through treatment) were not supported and regular in situ net washing is the only option to ensure nets remain free of fouling if copper treatment is not used. Based on the information from this project, the company has prepared production plans for the next 2-5 years that includes in situ net washing.

A further success of the project was that University of Victoria Master’s student Courtney D. Edwards used this project as part of her research. This enabled a student to work collaboratively with an industry leader and build a strong research relationship for the benefit of both parties. 

Ongoing work will include tests for net fatigue from continuous washing on currently used nets and on new rigid net materials. 

Project Lead: Marine Harvest Canada Inc.

Total Project Cost: $1,799,132
           
DFO-AIMAP Contribution: $200,000

Other Financial Support:

• Recipient: Marine Harvest Canada Inc.

For more information please contact the regional coordinator.

Pacific Region: Sean.Irvine@dfo-mpo.gc.ca