New case study: NAMAqI – a new approach to monitoring aquaculture impacts

Examining the use of sulphides as an analytical tool

Some 'high-energy' aquaculture sites have strong currents that disperse organic waste from farms, making it more challenging to predict and monitor environmental impacts.

When waste decomposes, it produces sulphides, including hydrogen sulphide, which can harm aquatic life by reducing oxygen levels and damaging fish health. Current monitoring methods rely on complex modelling and detailed analysis of seabed organisms (macrofaunal IQI), which can be costly and time-consuming. While tools like NewDEPOMOD - a computer modelling tool used in aquaculture to predict how organic waste from fish farms - have improved predictions, gathering and correlating biological data remains a regulatory requirement and a practical challenge.

The project explored whether measuring sulphide levels in seabed sediments could provide a faster, cost-effective way to assess environmental health at dispersive sites. Valued at over £260k, the project partners were the University of Stirling, Cooke Aquaculture  Ltd. (Orkney and Canada), Dalhousie University (Canada), and SAMS.

The project team, working with regulators in Scotland (SEPA) and Fisheries and Oceans Canada (DFO), conducted fieldwork at six salmon farms - three in Orkney and three in Nova Scotia - during peak production periods. Samples were analysed for sulphide concentrations, carbon content, and benthic community health, and compared with model outputs.

Findings suggest that sulphide measurements can indicate ecological status: low sulphide levels correlate with healthy seabed communities, while levels above 1500 µM signal poor conditions. However, results also showed variability, particularly at high-energy sites where biological communities may tolerate higher sulphide levels. This means sulphide testing cannot fully replace traditional macrofaunal analysis but could serve as a useful screening tool to target more detailed investigations.

The study also highlighted the need for improved measurement techniques, as the ion-specific electrode method used faced accuracy challenges. Alternative approaches, such as spectrophotometric analysis, may offer better precision.

The full title of this project is ‘NAMAqI: a novel approach to monitoring aquaculture impacts’

Read the case study