Modelling aquaculture impacts

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Modelling aquaculture impacts
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MOM (Modelling - Ongrowing fish farms -
Monitoring)

• This model developed in Norway is a three
  component model for modelling organic impacts.
• The fish sub-model simulates the release of
  particulate material from the farm based on
  information on the feeding rate and composition
  of food. Uptake, retention and excretion are all
  calculated in relation to the temperature and
  size of the fish.
• The output from this sub-model provides the
  initial conditions for the dispersion sub-model
  which simulates dispersion and sedimentation
  rates of excess feed and faecal pellets.
• The sediment sub-model calculates the maximum
  decomposition at the seabed for a particular
  scenario and oxygen concentration in the benthic
  boundary layer is also calculated.
• The combination of these sub-models allows the
  calculation of maximum fish production that a
  site can sustain without adverse benthic effects.

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AWATS - Aquaculture Waste Transport Simulator

• The AWATS model is a mathematical model to
  simulate tidal and wind-driven currents, waves,
  and the resulting dispersion of fish food and
  faecal matter in coastal areas.
• This model was one of the first aquaculture
  organic impact models to include complex models
  of the descriptions of spatially varying current
  around the study area.
• In addition, wind driven flow and waves are also
  included as processes having an effect on the
  subsequent dispersal of discharged particulate
  material.
• This model originally lacked resuspension which
  causes deposited particles to be re-entrained
  into near bed flows and advected away from the
  initial footprint area.

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DEPOMOD

• This model is a lagrangian particle tracking
  model which predicts the dispersion of
  particulate wastes arising from aquaculture
  activities and associated benthic impacts.
• It was developed from a sewage dispersion model
  also developed by SAMS, but required extensive
  modification to data input requirements and
  validation for the fish farming environment.
• There are three main modules
• particle tracking,
• resuspension
• benthic response.
• Predictions of solids accumulation (g m-2 yr-1)
  determine the benthic response using a
  relationship between solids accumulation and
  benthic indices validated for Scottish fish
  farms.

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• Current profiles in stratified waters are
  complex. Particles settling at different rates
  are subject to current shear and turbulence

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MERAMOD

• Is a conversion of Depomod from cols water areas
  to temperate areas
• There is an addition of wild fish component to
  take into account the utilisation of waste feed
  by wild fish under the cages
• It also takes into account the different species
  and behaviour of faecal pellets in the water
  column.
• It is validated for cage farms in the
  Mediterranean

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• MERAMOD modules (I)

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• MERAMOD modules (II)

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Crucial input data for modelling

• There are a number of key input data issues which
  need to be addressed when developing an existing
  model for application in a different environment.
  Although the principal physical processes can be
  applied to different areas, the input data used
  to drive these components need to be critically
  assessed.

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Sediment trap experiments (model validation)
Water column (WC)
Upper (U)
Lower (L)
x6
x6
x6 or x12
1. Deploy 2. Retrieve, filter, dry 3. Calculate
observed flux (total waste particulate material
g solids m-2 yr-1) 4. Check calculation
75 cm HD 51 ratio
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Typical impact footprints
Dispersive sites Strong currents Impact over a
larger area (up to 100 m) but less
intense Typical of fish farms in
Scotland Depositional sites Weaker
currents Impact over a limited area (up to 30
m) But more intense Typical of farms in Greece
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Model validation
Species Abundance
Use benthic data to establish relationships
between benthic indices and flux predictions
Shannon Weiner
Modelled flux (g m-2 yr-1)
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Use of models in knowledge transfer
Closely spaced cages Largely spaced
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Sedimentation 4 cages weak current
Sensitive habitats
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Sedimentation 4 cages strong current
Sensitive habitats