This 3,200-tonne Atlantic salmon farm on Loch Linnhe in the Scottish Highlands operates 10 cages in a sheltered sea loch environment with heavy seasonal biofouling. The fouling community is dominated by the hydroid Ectopleura larynx from May through July, transitioning to blue mussel (Mytilus edulis) dominance from August onward, with barnacle (Balanus crenatus) settlement peaking in late summer. The farm had been cleaning on a fixed fortnightly schedule but suspected this was not optimal given the shifting fouling community composition throughout the season.
Over two consecutive production seasons (2019-2020), the farm systematically compared three cleaning frequencies — weekly, fortnightly, and monthly — using in-situ rotating disc cleaners, with two cages assigned to each treatment and four cages maintained on the existing fortnightly schedule as controls. Weekly cleaning kept net occlusion consistently below 15 percent and maintained dissolved oxygen above 7.5 mg/L throughout the fouling season. Monthly cleaning proved inadequate, with occlusion reaching 60 percent by mid-August and measurable drops in dissolved oxygen below 6 mg/L in bottom net sections. Fortnightly cleaning — the farm default — maintained acceptable conditions (occlusion below 30 percent) except during a three-week mussel settlement peak in late August when it was insufficient. The optimal strategy proved to be fortnightly cleaning with an additional mid-cycle clean during the peak mussel settlement window, reducing annual cleaning costs by 18 percent compared to a blanket weekly schedule.
The fouling season calendar provides timing data for other UK and Nordic regions. Check the aquaculture farm map for site-specific fouling intensity, and use the biofouling cost calculator to compare costs across different cleaning frequencies. The solutions comparison tool evaluates mechanical cleaning alongside preventive approaches.
Outcomes
Tested weekly vs fortnightly vs monthly cleaning schedules using in-situ disc cleaners. Weekly cleaning kept net occlusion below 15% throughout summer. Monthly cleaning allowed 60% occlusion and measurable drops in dissolved oxygen. Optimal balance found at fortnightly intervals — cost-effective with acceptable fouling levels.