Introduction
Most Norwegian fish farms consist of plastic (polymer) structures such as floating platforms made of polyethylene pipes, nets made of nylon yarn, and moorings of synthetic ropes. During recent years, discarded aquaculture structures are increasingly considered a resource for reuse or recirculation of materials. Estimates from 2017 indicated that Norwegian Aquaculture facilities consisted of up to 192 000 tons of plastic components (Hognes & Skar, 2017; Sundt et al., 2018).
To establish sustainable circular business models , it is essential to understand which plastic resources , i.e. used equipment, that will be available during the next years. Thus, an early goal in the SirkAQ project (https://sirkaq.com/) has been to establish an overview of types and amounts of polymer materials in Norwegian fish farming structures.
Materials and methods
This work includes an analysis of the amount , geographic location, composition, quality, age and condition of plastic components used in sea-based farms during 2022. It is limited to plastic components of large volumes, i.e. floaters, nets and mooring lines , and feed pipes due to their frequent replacement.
Nine in-depth i nterviews of suppliers of plastic equipment were the main source of information. Semi-structured interviews were performed with the goal of answering the following research question: How much plastic can be found in Norwegian fish farms at sea, and what properties do they possess that are important to consider when deciding on their future use?
In the analysis, biomass reports (https://www.fiskeridir.no) and literature ( McIntosh et al., 2022 ) were used to establish the number and geographic location of farms and floaters used in 2022.
Results
We have estimated that a total of 5800 plastic fish pens could be found in Norwegian fish farms during 2022. About 91% of Norwegian fish pens were made of mainly plastic materials. There were 823 active fish farms along the Norwegian coastline , also including a minority of traditional steel cages and new types of fish farms (Føre et al., 2022).
Norwegian fish farms consisted of about in total 230,000 tonnes of plastic during 2022 . The total amount of plastic in floating collars and bottom rings was about 175,000 tonnes. T here were about 30,000 tonnes of nets in use, 21,000 tonnes of ropes in the mooring systems, and 3,300 tonnes of feed hoses. The analysis shows that over 80% of the mapped plastic was Polyethylene (PE), of which 66% was virgin HDPE 100. Furthermore, we found 10% Nylon, 6% polyolefins in the form of PE/PP, 3% PE/PET, and 1% UHMWPE. There are also smaller amounts of Polypropylene (PP).
The typical practical lifetime is around 15 years for cage collars, about eight years for nets (including storage between use), 10 years for mooring lines, and on average 1.5 years (one production cycle) for feed pipes. The plastic materials in discarded equipment are often in good condition.
Acknowledgement
The work is done as part of the project “SIRKAQ” which is founded through the Norwegian Government “Green Platform Programme” (project no. 340887), with funding from the Norwegian Research Council, Innovation Norway and SIVA, in addition to funding from the Norwegian Retailers’ Environment Fund.
References
Føre, H.M., Thorvaldsen, T., Osmundsen, T.C., Asche, F., Tveterås, R., Fagertun, J.T., Bjelland, H.V., 2022. Technological innovations promoting sustainable salmon (Salmo Salar) aquaculture in Norway. Aquaculture reports 24, 101115, https://doi.org/10.1016/j.aqrep.2022.101115.
Hognes, E. S., & Skaar, C. (2017). Avfallshåndtering fra sjøbasert havbruk. SINTEF report OC2017 A-218.
P. McIntosh, L.T. Barrett, F. Warren-Myers, A. Coates, G. Macaulay, A. Szetey, N. Robinson, C. White, F. Samsing, F. Oppedal, O. Folkedal, P. Klebert, T. Dempster, 2022. ‘Supersizing Salmon Farms in the Coastal Zone: A Global Analysis of Changes in Farm Technology and Location from 2005 to 2020’. Aquaculture 553 (15 May 2022): 738046. https://doi.org/10.1016/j.aquaculture.2022.738046.
Sundt, P., Briedis, R., Skogesal, O., Standal, E., Rødås Johnsen, H., & Schulze, P.-E. (2018). Underlag for å utrede produsentansvarsordning for fiskeri- og akvakulturnæringen (M-1052|2018).