 Modelling discharges and environmental effects from aquaculture
Akvaplan-niva was coordinator for the
MERAMED project, a
Research and Development project supported by the EU. The project
provided guidelines for the creation and application of a
comprehensive monitoring system to assist the regulation of marine
cage fish farms in the Eastern Mediterranean. Central in the project
was the development of a modelling tool. The MERAMOD model is
a further development of DEPOMOD, a model used for salmon farming in the Atlantic. MERAMOD takes into
account a wider range of environmental conditions and farmed
species. The model is verified for sea bass and bream farming in the Eastern Mediterranean.
MERAMOD calculates flux to the sea floor using
- Topography, location, bathymetry
- Cage specific data (species and sizes, food input via growth
model, hydrographic data, diurnal patterns of feed and faecal release)
- Particle tracking data (faecal and feed particles settling
rates, turbulence, shear, advection, resuspension)
- Wild fish effects (wild fish may remove wasted pellets an
faeces released from farm cages)
The resulting flux predictions are then put into the benthic response
module which will calculate effect zones.
Using MERAMOD, a number of management scenarios were compared.
These scenarios show that cages at deeper, dispersive sites result
in less severe impact over a larger area. In addition, spacing out
of cages reduces predicted deposition markedly especially where a
large spacing is used. The modelling also suggests bass potentially
have more impact than bream as a result of faster faecal settling
velocities, despite the slightly lower feed input used for bass.
Therefore, bass should be sited in deeper more dispersive sites or,
where farmed at the same site as bream, bass should be placed in the
outer (deeper) areas of the farm.
The effect of inefficient feeding and high stocking density was also
clear. A more severe impact over a larger area will result, with a
higher probability of problems with sediment and fish health.
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