Mitigating the environmental effects of mariculture through single-point moorings (SPMs) and drifting cages

The production of finfish in cages causes a measurable impact on the nearby water and seabed due to faeces production and uneaten Feed. The impact depends on the specifics: of the culture operation and on the environment in which it is located. The most severe impact has been associated with large. intensive operations in areas with inadequate water circulation, where benthic habitats have been seriously degraded. The current practice of mooring a cage. or a cage array, over a permitted site exacerbates the problems. An alternative approach is to allow cages to move in response to the environment. For example, the use of a single point mooring (SPM) would allow the operation to maintain a "watch circle" where the position of the cage(s) depends on the sum of the environmental forces. By spreading out the accumulation of organic matter. one can prevent the local environment From being overwhelmed. Preliminary analyses of the benefits of SPM indicate ii two-fold to 70-fold reduction in deposition of waste on the seabed, depending on mooring geometry and current type. Other advantages are related to reduced anchoring costs, improved accessibility, and the ability of having certain cages in the lead position with respect to currents and good oxygen conditions, The concept of drifting cages is introduced as a Further alternative to minimizing impact on the seabed. (C) 2001 International Council for the Exploration of the Sea.