This large-scale salmon farming company operates sites at both exposed offshore locations in the Frohavet area and sheltered inshore positions within Trondelag fjords along the central Norwegian coast, producing a combined 8,000 tonnes annually. The operator had long observed that offshore cages required less frequent cleaning than inshore ones but lacked quantitative data to optimise cleaning schedules for each location type. A structured two-year monitoring programme was established to compare fouling development, community composition, and the resulting impact on cage net permeability across four offshore and four inshore sites.
The monitoring confirmed that exposed offshore sites accumulated approximately 40 percent less total fouling biomass than sheltered inshore sites over equivalent deployment periods. The fouling community also differed markedly: offshore cages were dominated by hydroids and filamentous algae, with very low mussel and barnacle settlement, while inshore cages developed the typical heavy mussel-barnacle community. The higher current velocities and greater wave exposure at offshore sites both inhibited larval settlement and physically removed weakly attached organisms. ROV-assisted cleaning every 3 weeks at offshore sites maintained net permeability above 80 percent — a level that required weekly cleaning to achieve at inshore locations. The operator subsequently adopted differentiated cleaning schedules, reducing annual cleaning expenditure by approximately 95,000 euros while maintaining equivalent production performance across all sites.
Both inshore and offshore site types are plotted on the aquaculture farm map with environmental exposure data. The solutions comparison tool can help determine appropriate cleaning methods for different exposure levels, the organisms database documents the species found at both site types, and the cost calculator enables comparison of cleaning costs across different schedule configurations.
Outcomes
Exposed offshore site with stronger currents showed 40% less fouling than sheltered inshore sites. Hydroid-dominated community rather than mussel-dominated. ROV cleaning every 3 weeks maintained net permeability above 80%. Wind and wave exposure naturally limited barnacle settlement.