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Summary of the method of categorisation of sea lochs and voes on the basis of nutrient release and impact of organic matter on the sea bed
Sea lochs and voes differ greatly in their capacity to support fish farming and accommodate the associated waste released by the farms. Discharged nutrients and solid waste can potentially interact with the pelagic compartment of the marine ecosystem (for example through enhancing primary productivity) or the benthic compartment (for example through deposition of organic matter on the sea bed). The potential scale of these interactions is strongly dependent upon the amounts discharged, the volume of the sea loch, and the degree to which waste is dispersed into the water surrounding the farm and into the wider marine environment outside the sea loch by the tidal current regime in the area. These features have been used to develop an index of the relative suitability of sea lochs for further fish farming development, taking into account the current level of development.
Mathematical models of the water circulation and exchange in sea lochs and voes have been used to provide indications of the relative scale of nutrient enhancement of the water column and organic enrichment of the sea bed arising from the current levels of fish farming. Dissolved nutrients released into a loch with a large tidal range and strong freshwater inflow will be more rapidly dispersed than nutrients entering a loch of a similar size but small tidal range and low freshwater input. Similarly, string tidal currents will lead to the dispersion of solid waste over a larger area, reduce the rate of deposition of waste on the sea bed, and increase the likelihood of the sea bed community to accommodate the waste. The relative level of nutrient enhancement and spatial extent of heavy organic deposition on the sea bed have each been scaled from 0-5, and the two scaled values added together to provide a single index.
On the basis of the resultant single index, sea lochs and voes have been categorised as follows:
Category 1: Index values of 7, 8, 9, or 10
Category 2: Index values of 5 or 6
Category 3: Index values of 0, 1, 2, 3 or 4
Summary of the method of categorisation of sea lochs, voes and coastal areas on the basis of natural heritage resource
Three broad categories of information were used to select sites.
1. Occurrence of designated sites – statutory and non-statutory – including: Sites of Special Scientific Interest; National Nature Reserve; Special Areas of Conservation; National Scenic Area and Marine Consultation Area.
2. The potential impact upon natural heritage interest outwith designated sites, including: landscape implications in relation to the recently prepared landscape character assessments, and; species and habitats which are listed under both domestic and European legislation or subject to actions plans being prepared as part of the UK Biodiversity Action Plan.
3. Extent of existing development – in terms of both the number of leases and scale of production.
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