Marine Harvest Canada
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
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 Courtenay 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. Communication of project information is ongoing and preparation of this report is the final requirement for the AIMAP funding.
Biofouling in salmon aquaculture is a costly problem, both environmentally and economically. The accumulation of fouling organisms on a fish cage negatively impacts cultured stock by occluding net openings, which reduces water flow and associated nutrient and oxygen exchange. It also physically damages nets and infrastructure. Biofouling is typically managed by the use of toxic copper-based coatings and time consuming manual cleaning.
In accordance with the Marine Harvest corporate objective of eliminating copper treated nets, during 2009 Marine Harvest began converting from copper dipped nets to untreated nets. To reduce biofouling, the untreated nets have bi-weekly net maintenance using manually operated high-pressure washers. This prevents the initial growth of mussels and other marine life. Net maintenance is a labour intensive operation and one which cannot be done safely in high seas, especially on farms with circle cages. Marine Harvest is upgrading one of its highest energy sites at Shelter Bay, near Port Hardy, British Columbia.
The overall goal of this upgrade and testing is developing a proven system of environmentally sustainable cages and nets capable of use at offshore, high energy sites. Marine Harvest purchased eight of the best offshore cages available, Aqualine 120m circles, for Shelter Bay and these were installed in September 2010. This project was the first opportunity for Marine Harvest to test cages and nets suitable for further offshore use.
Over six months, alternative nets were tested in a controlled study using traditional nylon nets as the control. The study took place on a fully operational commercial salmon farm site (Shelter Bay, operated by Marine Harvest Canada).
For the duration of the project the site had seven 120m diameter polar circle cages (made by Aqualine®) set up in a double array. The untreated Dyneema®, Dyneema+Sancure® and untreated nylon cages were deployed in January 2011. The ThornD® net was late in arriving from the manufacturer in Europe, and proved to be structurally unsound. To be able to include this net in the study, adjustments were made and the net was deployed in February but did not have any fish in it. Panel samples were entered in January 2011. Atlantic salmon (Salmo salar) were entered on February 14, with up to 75 thousand in each polar circle.
Dyneema is an ultra-high-molecular-weight polyethylene (UHMwPE) fibre created by the Dutch chemical company DSM®. The material is 15 times stronger than steel, chemically inert; UV, abrasion and moisture resistant; and very durable (Dyneema 2011). Nets made with Dyneema do not absorb water, retain their knot strength and have limited stretch. The Dyneema net has a somewhat rectangular twine thickness of 2mm wide and 1mm thick.
Nylon is a name that encompasses various synthetic, thermoplastic polymers which are considered to be fairly tough, lightweight and resistant to heat and chemicals. Nylon netting absorbs water and can lose 10-20% of knot strength when submerged (Badinotti 2011). Nylon netting has a round twine thickness of ~3mm.
ThornD is a coating designed specifically to prevent biofouling. The coating is applied by flocking short fibres onto the netting material. This "fuzzy" surface is thought to deter settling organisms by damaging planktonic cell structure and by swaying with water movement thus dislodging spores (Micanti 2011). Nylon net with a ThornD coating has a round twine thickness of ~5mm ±1 due to the varying length of the fibres.
Sancure 1511 (manufactured by Lubrizol Advanced Materials Inc.) is an aromatic waterborne urethane polymer. It has a high gloss, is abrasion resistant and flexible. The coating was supposed to cause the fibers to adhere together, and solve the issue of loose fibers that occurred on a large section of the Dyneema net. Sancure does not alter the initial twine thickness.
The monthly biofouling evaluation was conducted by video monitoring of the salmon cages and a controlled, statistically viable panel-study which was monitored with still images.
Although some statistically significant results were found throughout this study none of the materials tested performed well enough at preventing biofouling to be considered effective by industry standards.
Despite the combinations having slightly different succession and disturbance patterns, species composition in September (which is considered to be the initial stages of the climax community) showed no significant difference between the combinations. This is supported by the percent net occlusion results which showed that all four combinations in this study finished at the roughly the same levels. The biomass results showed that the Dyneema net has potential to somewhat reduce biomass; and the ThornD net generally showed higher levels of biomass. There was no difference in biofouling between the untreated and treated Dyneema. Dyneema treated and untreated nets were considerably more costly than other options with a non-significant difference in biofouling results.
Although a combination‘s ability to prevent the accumulation biofouling remains an important factor in choosing a netting material and coating, the current state of environmentally benign antifouling technology means that other factors need also be considered. These factors include: the cost effectiveness of a new material or coating, the strength and lifespan of a material and its associated repair and maintenance costs, and a reduction in overall surface area by having larger mesh and finer twine. This study exemplifies the diversity and tenacity of fouling organisms and the challenge all marine ventures face when working in this biologically diverse environment.
The Dyneema net performed the best in other criteria. It is easiest to use, is substantially stronger and does not lose strength when wet. It also has a smaller twine thickness reducing surface area for biofouling. Relative to other nets, the reduced biofouling creates less drag and reduces the need for net washing.
No difference was observed in predator reactions and there was inadequate data to compare fish growth between the nets. The Dyneema net has a greater capital cost than the other options but was rated as “Far Superior” in durability and “superior” for handling.
The project was extended to October 31, 2011 with the final report submitted by December 31, 2011. This extension was necessary due to severe winter weather that delayed installing nets and fish at Shelter Bay until late January 2011.
The ThornD® net was late in arriving from the manufacturer in Europe, and proved to be structurally unsound. It failed mesh break testing and since the net could not be relied on to hold fish it was decided not to spend more money completing the net bottom. To be able to include this net in the study it was deployed in February but did not have any fish in it.
Due to the delay in the ThornD net arrival, the biofouling evaluation and net performance evaluation was completed during the summer of 2011.
The project total cost was estimated at $1.8M at the time of funding application. At completion, the project expenses totaled $2.8M (cash $1.5M and inkind $1.3M) with the additional costs covered by Marine Harvest. AIMAP funding contribution of $196,000 was used for purchase of nets in the study. All purchases were complete prior to March 31, 2011.
This project successfully provided Marine Harvest with definitive evidence that the claims made by the various net manufacturers either for the biofouling resistant materials or for specific net treatments were not supported and that another method of keeping the nets clean was required. This valuable information has provided the basis of long term production plans (2-5 years) that now include regular net washing as the method of ensuring the nets are kept free of fouling.
All evaluation of biofouling and net performance is complete. Project information will be provided to stakeholders upon request. Future research on resilience of various net materials to continuous washing is planned.