A scientific report has been published on aquaculture emissions in the Hardangerfjord environment.
- Hardangerfjord is not currently over-fertilised, but researchers have stated that the area cannot withstand further emissions
- Fish sludge (excess feed and faeces) is a contributor to emissions of organic particulate matter but also dissolved bioavailable nutrients. Managing sludge is therefore key for scaling production sustainably and safeguarding the environment
- The EU-funded project AQUAPHOENIX is testing scalable solutions to manage sludge and reduce emissions. Project partners are currently testing novel sludge collection technologies with industry partners in Hardangerfjord
A comprehensive report on aquaculture emissions in Hardangerfjord has been published by the Institute for Marine Research (IMR), commissioned by the Norwegian Environment Agency.
The report assesses current emission levels and the risks of eutrophication (excess levels of nutrients like phosphorus and nitrogen, which affect the balance of the marine environment).
Their calculations show that of the 56 total fish farming facilities in Hardangerfjord, 3,500 tonnes of dissolved nitrogen and 500 tonnes of dissolved phosphorus are released per year. The resulting increase in phytoplankton production is below the limit for eutrophication set by the OSPAR Convention, a regional agreement to conserve the Northeast Atlantic. No evidence of eutrophication was found at the measurement sites.
Hardangerfjord can tolerate current emissions, but nutrients are a limiting factor for increasing production
Stakeholders, including those across industry and policy, have expressed a desire to increase aquaculture production in Hardangerfjord to ensure continued growth and meet increasing food demand. After simulating the effects of increased production, researchers cautioned that increasing production carries an increased risk of over-fertilisation.
The report details how discharges of sludge (excess fish feed and faeces) spread dissolved nutrients through the water column, as well as how organic particulate matter beneath aquaculture facilities affect the seabed ecosystem. Increasing production risks increasing the amount of sludge particles in the water column and seabed, and carries a risk of over-fertilisation in parts of the fjord, leading to oxygen loss of deep water and seafloor sediment.
A novel approach to sludge management is therefore needed to scale up production while managing emissions and protecting the marine environment.
AQUAPHOENIX – an EU-funded research and innovation project – pilots a novel approach to manage sludge and emissions
A NOK 120 million (€8.7m) project, financed by the European Union and bringing together partners from Norway, Finland, Sweden, Belgium, and The Netherlands, is responding to the need to manage emissions from sludge.
In January 2025, partners launched AQUAPHOENIX to develop and test innovative technologies for collecting the sludge that accumulates below aquaculture facilities. Observations on the resulting environmental responses on the seafloor and in the water column will be incorporated into a hydrodynamic modelling context. Pål Sævik from IMR, co-author of the report and leading the work package on pelagic (water column) impacts in AQUAPHOENIX, explains: “Novel modelling approaches will enable interpreting the observed effects on a regional level, informing stakeholders about possible benefits of large-scale deployment of sludge collection technology.”
While research institutions including NORCE and IMR will evaluate the impact of sludge collection on the marine environment, industrial players Framo and Ragn-Sells will contribute efforts to collect sludge and valorise sludge byproducts into renewable assets like novel feed and fertilizer ingredients and clean energy.
“Through AQUAPHOENIX, we are testing low-emission technologies that can reduce the environmental burden and support sustainable aquaculture, while also exploring governance options that can help ensure these solutions are implemented effectively to give the intended impact”, says Hans Kleivdal, Deputy EVP and Head of Business Development in NORCE Climate & Environment.
Reference: V. Husa et al. Hardangerfjorden under press – Utslipp og miljøtilstand. Rapport fra havforskningen, 2025-66.
