Scotland’s salmon industry is concentrated along the west coast and through the Hebrides, Orkney, and Shetland — sheltered sea lochs and exposed island sites that each present different fouling challenges.
Sea lochs on the mainland (Loch Linnhe, Loch Fyne, Loch Sunart) tend toward heavy fouling loads. Restricted water exchange and nutrient runoff from surrounding land create conditions that favour dense hydroid, mussel, and tunicate growth. In Loch Linnhe, farms report net occlusion rates above 60% within four weeks during peak summer if cleaning is delayed.
Island sites — Shetland, Orkney, the Outer Hebrides — deal with more exposure and stronger tidal flows. Fouling biomass accumulates slower, but hard foulers like calcareous tubeworms (Serpula vermicularis) are more of a problem. In Shetland, serpulid aggregations on cage frames and mooring equipment require heavy mechanical scraping, and damaged coatings are a recurring maintenance cost.
Scottish regulators have introduced Environmental Management Plans for farm sites, which increasingly include fouling waste discharge as a factor. The fouling debris released during net cleaning — fragments of mussels, hydroids, shell material — sinks to the seabed beneath cages and contributes to benthic loading. Some licences now require debris collection systems during cleaning operations.
Net cleaning contractors dominate the Scottish market. Most farms hire specialist vessels rather than owning cleaning equipment outright. The typical schedule is fortnightly during summer, monthly in spring and autumn, and minimal through winter. See the fouling season calendar for Scottish timing and use the aquaculture farm map to explore site locations.