Analysis of Coastal and Offshore Aquaculture: Application of the FARM Model to Multiple Systems and Shellfish Species

The Farm Aquaculture Resource Management (FARM) model has been applied to several shellfish species and aquaculture types. The performance of the FARM model, developed to simulate potential harvest, key financial data, and water quality impacts at the farm-scale, was tested in five systems in the European Union: Loch Creran, Scotland (Pacific oyster), Pertuis Breton, France (blue mussel), Bay of Piran, Slovenia (Mediterranean mussel), Chioggia, Italy (Mediterranean mussel) and Ria Formosa, Portugal (Manila clam). These systems range from open coasts to estuaries, and are used for shellfish aquaculture by means of different cultivation techniques (e.g. oyster bottom culture in Loch Creran and mussel longlines and poles in Pertuis Breton). The drivers for the FARM model were supplied by measured data, outputs of system–scale models or a combination of both.

The results (given in total fresh weight) generally show good agreement with reported annual production (shown in brackets) at each farm: simulated production of 134 t of Pacific oyster in Loch Creran (150 t, −10%), 2691 t of blue mussel in Pertuis Breton (2304 t, +17%), 314 t of Mediterranean mussel in the Bay of Piran (200 t, +57%), 545 t of Mediterranean mussel in Chioggia (660 t, −17%) and 119 t of Manila clam in Ria Formosa (104 t, +15%). The nitrogen mass balance for each farm was also determined with the FARM model. The net removal of nitrogen (N) by the farms was estimated to correspond to 1151 population equivalents per year (PEQ y⁻¹) in Loch Creran, 39505 PEQ y⁻¹ in Pertuis Breton, 210 PEQ y⁻¹ in the Bay of Piran, 7108 PEQ y⁻¹ in Chioggia and 8748 PEQ y⁻¹ in Ria Formosa. The aggregate income due to both the shellfish sale and substitution value of land-based fertilizer reduction or nutrient treatment was estimated to be about 680 k€ y⁻¹ in Loch Creran, 14930 k€ y⁻¹ in Pertuis Breton, 220 k€ y⁻¹ in the Bay of Piran, 2560 k€ y⁻¹ in Chioggia, and 5040 k€ y⁻¹ in Ria Formosa. Outputs of FARM may be used to analyse the farm production potential and profit maximization according to seeding densities and/or spatial distribution. Results of a marginal analysis for all the study sites were determined. As an example, profit maximization in Loch Creran was obtained with 97 t of seed, resulting in a total production of 440 t (profit of 2100 k€ for a culture period of about 2 years). FARM additionally integrates the well-known ASSETS model, for assessment of farm-related eutrophication impacts. The assessment results for the five study sites show that water quality is either maintained or improved in all farms under standard conditions of culture practice.

FARM results may be used by farmers to analyse farm production potential and by managers for environmental assessment of farm-related water quality impacts, whether positive or negative. It is a useful tool for all stakeholders for the valuation of nitrogen credits, which may be traded as part of an integrated catchment management plan.