TROPOMOD modelling for optimisation of
AquaParks
Chris Cromey – EMMA2 project modeller using data from Akvaplan
and BFAR s...
TROPOMOD educational software
Currents move in different speeds and direction at
different depths. Faeces settle more slowly and so
are transported furt...
Contour map of waste flux
Benthic
community

(grams waste feed and faeces m-2 d-1)

-2
-1
grams solids m bed d
75

Severe ...
TROPOMOD – validation with
sediment traps
Cage

Current
Sea bed

1. Deploy traps
75 cm

2. Retrieve, filter, dry solids

H...
TROPOMOD model validation – comparison of
observed and modelled flux

Comparisons between modelled and observed flux for S...
TROPOMOD validation – relationships between
predicted flux and indicators of impact - Sual

Where
TROPOMOD
predicted high
...
TROPOMOD
validation –
relationships
between predicted
flux and indicators of
impact - Panabo

Organic Carbon as
also found...
Criteria for AquaPark zoning

Regular spacing
between cage
groups to allow
flushing

Regular spacing
between zones to
allo...
Compare with the
current situation

Current flow
restrictions due to
high density of
cages, with no gaps
Criteria for AquaPark zoning - impact

Within each
zone
MODERATE
impact (green)
or less between
cage groups
MODERATE
impac...
Suspended/raft culture (e.g.
oysters) - majority of the wastes
intersect the culture in the top 10
m; these wastes are mos...
Sual AquaPark – Existing and reorganised

Less SEVERE impact under cages
between zones

MODERATE impact
Panabo AquaPark – Existing and offshore zones added

Good feeding scenario improves inshore areas
Offshore Milkfish zones ...
Panabo AquaPark – Existing and reorganised

Spacing between zones results in less impact and also more space for IMTA unit...
Criteria for AquaPark zoning – IMTA location
Seaweed culture – located 10+
m from cage groups along the
axis of group
IMTA...
Sual AquaPark and IMTA close to the cages
Seaweed

-2 -1

Flux (g m d )

Oysters

Benthic
Community
Severe impact
(no anim...
Panabo AquaPark and IMTA close to the cages

Large oyster culture
zones were placed
inshore of the
finfish zones.

Smaller...
Recommendations for site optimisation
• Regular spacing of cages and good separation between zones enhances
current flushi...
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Modelling environmental impact of cages (Tropomod)

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Modelling environmental impact of cages (Tropomod). The TROPOMOD model is a particle tracking model which simulates the dispersion of waste feed and waste faecal particles from fish cages. Using depth and current velocity data from environmental surveys and husbandry data such as cage layouts and feed ration from production surveys, TROPOMOD was used to predict flux of waste solids to the sea bed (grams waste feed and faeces m-2 sea bed day-1). This was then related to a level of impact on the sediment benthos. The model was used to examine the existing situation at the Sual and Panabo AquaParks and then test various scenarios for site optimisation and future production of the AquaParks.

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Modelling environmental impact of cages (Tropomod)

  1. 1. TROPOMOD modelling for optimisation of AquaParks Chris Cromey – EMMA2 project modeller using data from Akvaplan and BFAR survey teams Modelling objectives for each AquaPark • Predict benthic impact for the existing situation and validate model with survey data • Predict benthic impact for expansion/reorganisation • Predict optimum location for Integrated Multi-Trophic Aquaculture units • Estimate of production and recommendations from modelling viewpoint Other objectives • TROPOMOD educational software showing different scenarios of impact
  2. 2. TROPOMOD educational software
  3. 3. Currents move in different speeds and direction at different depths. Faeces settle more slowly and so are transported further away from cages 0 Current Velocity Source Milkfish waste faeces settle very slowly Fine Coarse Medium Waste feed particles settle quickly
  4. 4. Contour map of waste flux Benthic community (grams waste feed and faeces m-2 d-1) -2 -1 grams solids m bed d 75 Severe impact (no animals) 75 15 High impact (some effect) Cages 15 1 Moderate impact 1
  5. 5. TROPOMOD – validation with sediment traps Cage Current Sea bed 1. Deploy traps 75 cm 2. Retrieve, filter, dry solids H:D = 5:1 ratio 3. Calculate observed flux (total waste feed and faeces in traps = grams per m2 bed per day) 4. Compare with TROPOMOD model
  6. 6. TROPOMOD model validation – comparison of observed and modelled flux Comparisons between modelled and observed flux for Sual (Offshore Milkfish) and Panabo (Inshore Milkfsh and Grouper) were satisfactory
  7. 7. TROPOMOD validation – relationships between predicted flux and indicators of impact - Sual Where TROPOMOD predicted high flux, sediments contained higher % of organic material
  8. 8. TROPOMOD validation – relationships between predicted flux and indicators of impact - Panabo Organic Carbon as also found to be high, where TROPOMOD flux predictions were high
  9. 9. Criteria for AquaPark zoning Regular spacing between cage groups to allow flushing Regular spacing between zones to allow flushing No cages near restrictions to allow current flow Only small Milkfish cages or Grouper cages in shallow areas near to shoreline Larger cages (polar circles) in deeper areas away from shoreline
  10. 10. Compare with the current situation Current flow restrictions due to high density of cages, with no gaps
  11. 11. Criteria for AquaPark zoning - impact Within each zone MODERATE impact (green) or less between cage groups MODERATE impact (green) or less between zones SEVERE impact (grey) under the cages was minimised
  12. 12. Suspended/raft culture (e.g. oysters) - majority of the wastes intersect the culture in the top 10 m; these wastes are mostly fine and slow settling Milkfish faeces Criteria for AquaPark zoning – IMTA location 18% 5% 0-3m 3% 6% 3-6m 2% 6-9m Reversing current <1% 9-12m 12-15m 25 m 10 m 0m 0m 10 m 25m Distance from cage edge (m) Seaweed culture - majority of the plume containing dissolved nutrients intersects the seaweed culture in the top 5 m Benthic culture (e.g. sea cucumbers) around 20% of wastes deposited within 10 m of the cages; not placed in very high deposition area under cages
  13. 13. Sual AquaPark – Existing and reorganised Less SEVERE impact under cages between zones MODERATE impact
  14. 14. Panabo AquaPark – Existing and offshore zones added Good feeding scenario improves inshore areas Offshore Milkfish zones in deeper areas results in good dispersion
  15. 15. Panabo AquaPark – Existing and reorganised Spacing between zones results in less impact and also more space for IMTA units
  16. 16. Criteria for AquaPark zoning – IMTA location Seaweed culture – located 10+ m from cage groups along the axis of group IMTA culture was minimal between cage groups to allow flushing Benthic culture – optimum location at end of cage groups, but not directly underneath Suspended culture – located 10+ m from cage groups along the axis of group
  17. 17. Sual AquaPark and IMTA close to the cages Seaweed -2 -1 Flux (g m d ) Oysters Benthic Community Severe impact (no animals) Sea cucmbers 75 Large seaweed and oyster culture zones were placed either side of the Milkfish culture zone. High impact 15 Moderate impact 1 Smaller IMTA zones were placed inbetween cage groups. Scale (m) 0 200 400 600 800
  18. 18. Panabo AquaPark and IMTA close to the cages Large oyster culture zones were placed inshore of the finfish zones. Smaller IMTA zones were placed inbetween cage groups. Some space available offshore, but deep.
  19. 19. Recommendations for site optimisation • Regular spacing of cages and good separation between zones enhances current flushing through the AquaPark and reduces impact between culture areas • Good spacing between inshore zones (min. 200 m) and offshore zones (min. 400 m) • Within a zone, good and regular spacing between cage groups (100 m) and between rows of cages (25 m) • Target FCR should be 2.0:1, as with careful feeding of a good quality feed, this allows a reduction in feed ration • IMTA suspended culture (oysters and seaweeds) should be minimum 10 m from cages • IMTA units should be placed along the axis of current flow leaving corridors for enhanced flushing and dispersion of nutrients

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