modelling of aquaculture impact and carrying capacity in the philippines using tropomod

© www.akvaplan.niva.no 1

TROPOMOD modelling of six SABBAC aquaculture zones

PHILMINAQ projectChris CromeyPatrick White

Cesar Villanoy, Evangeline MandongAll of the PHILMINAQ team made

contributions to this modelling effort


Particles settling under a fish cage

result in a ‘footprint’ of deposition of solids on the sea bed


Currents move in different speeds and direction at different depths. Faeces settle more slowly and so are transported further away from cages

0 C u rre n t V e lo c ity

S ou rce

C o a rse M ed iu m

F in e

Waste feed particles settle quickly

Milkfish waste faeces settle very slowly


Benthic community

Severe impact

(no animals)

High impact (some effect)

Moderate impact

Contour map of waste flux

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

75

15

1

grams solids m bed d-2 -1

1

1 5

7 5


PHILMINAQ project modelling approach with TROPOMOD

3 important aspects:

1. How severe is the impact – what is the maximum impact underneath cages?

2. How far to the boundary of the impact? (Scotland = Allowable Zone of Effect)

3. How can husbandry practices be optimised to use the zone most productively?

Objectives

Predict if impact is SEVERE underneath cages

as shown by this deposition footprint

Zone colour

Predict distance to boundary of MODERATE impact

Zone colour

Edge of zone



Maintain enough spacing between cage rows so that remediation of sediments can take place – impact should be LOW between rows in each zone

Maintain enough space between cage rows to prevent reduction of currents by high aggregation of cages

Zone colour

Not predicted by TROPOMOD, but this effect is known to exist and has been shown by MSI models



Encourage careful feeding, so that there is less waste feed and less wastage of money

Encourage better quality feed: Feed digestibility is increased Less feed is needed Better quality feed also breaks up less, so more goes to growth

Test these scenarios

Prevent overlap of zones by predicting the extent of the zones – e.g. 600 m between zones for this site

0 200 400 600 800Scale (m )


Method - common model input data between scenarios

Model input data Value

Zone size 600 m by 200 m (12 ha)

Current (modelled by MSI) Modelled

Feed settling rate for different scenarios

FCR 2.8 – pellet break up (estimated)

FCR 2.0 – intact pellets (measured by PHILMINAQ)

8.9 cm/s (5%), 4.5 cm/s (65%), 1.6 cm/s (30 %)

8.9 cm/s (100%)

Faeces settling rate – measured by PHILMINAQ for Milkfish

0.84 (cm/s)


Model input data Scenario 1

Poor feeding

Low digest.

Scenario 3

Careful feeding

Better digest.

Feed wasted 27% 10%

Feed digestibility 49% 56%

FCR 2.8:1 2.0:1

Feed input Between 0 and 323 kg/cage/d

Between 0 and 231 kg/cage/d

Scenarios tested

A range of feed inputs are used between 0 and maximum to simulate fish at different stages of growing cycle in each zone

Therefore, these are not worse case scenarios

Method – what is varied between scenarios?

Data source: EMMA and PHILMINAQ projects


Days Size Number Biomass(kg)

Feed rate (%/day)

Feed/day(kg)

April 0 0 0 0 0 0

May 25 20 27247 545 8.5 46

June 30 41 26873 1091 8.9 97

July 31 91 26498 2406 7.1 171

August 31 162 26124 4224 5.1 214

September 30 247 25749 6358 4.4 278

October 31 386 25375 9799 3.3 323

November 19 433 25000 10825 1.8 193

Square cages – 12m * 12m * 8m

Zones 1 – 3, 5 and 6: feed ration used in the simulations – each cage randomly allocated a feed ration to simulate fish at different stages of cycle

FCR = 2.8:1

Data source: EMMA project


Days Size Number Biomass(kg)

Feed rate (%/day)

Feed/day(kg)

April 0 0 0 0 0 0

May 25 20 59444 1189 8.5 101

June 30 41 58628 2404 8.9 214

July 31 91 57810 5261 7.1 374

August 31 162 56994 9233 5.1 471

September 30 247 56176 13875 4.4 611

October 31 386 55360 21369 3.3 705

November 19 433 54542 23616 1.8 425

Large circular cages – 20m diameter * 8m means 2.18 times more

biomass can be contained in cages if stocking density is maintained

Zones 4: feed ration used in the simulations – each cage randomly allocated a feed ration to simulate fish at different stages of cycle

FCR = 2.8:1

Data source: EMMA project data on previous slide scaled by 2.18


Current used in TROPOMOD were taken from the MSI hydrodynamic model of the area (left) – 30 days of current were used

Zones 1 to 6 are shown in the map

Aquazones identified by the hydrodynamic model


-35

-25

-15

-5

5

15

25

35

-35 -25 -15 -5 5 15 25 35

Zone 1

-35

-25

-15

-5

5

15

25

35

-35 -25 -15 -5 5 15 25 35

Zone 2

-35

-25

-15

-5

5

15

25

35

-35 -25 -15 -5 5 15 25 35

Zone 3

-35

-25

-15

-5

5

15

25

35

-35 -25 -15 -5 5 15 25 35

Zone 4

-35

-25

-15

-5

5

15

25

35

-35 -25 -15 -5 5 15 25 35

Zone 5

-35

-25

-15

-5

5

15

25

35

-35 -25 -15 -5 5 15 25 35

u (cm/s)v

(cm

/s)

Zone 6

Current velocity distribution

e.g. At zone 1, current is flowing east and west in the Bolinao Narrows

For each site, lines of cages were orientated parallel with the main axis of current e.g. cages in zone 4 were aligned NE-SW

North


Zone Depth (m) Depth rank

Mean speed (cm/s)

Max speed (cm/s)

Current rank

1 20 1 10.8 28.6 3

2 14 2 11.5 30.6 2

3 13 3 8.9 23.7 4

4 10 4 7.9 24.8 5*

5 10 5 6.0 18.8 6

6 9 6 13.3 39.9 1

Modelled current at the zones from MSI Bolinao model showing a rank of the most dispersive and deepest

This table shows tidal currents – site 4 is exposed to waves from the east, which will increase dispersion


Definitions Zone colour Predicted flux (g m-2 d-1)

Impact areas:

Low/None

Moderate

High

Severe

<1

1 – 15

15 – 75

75 +

% of zone area HIGH and SEVERE impact

>15

Is more than 1 % of zone SEVERE impact? Yes or No?

> 75

Distance to boundary of zone of effect - 1 g m-2 d-1 contour

1

Measured sediment flux at Bolinao during workshops by PHILMINAQ project - 114.0 g m-2 d-1 (0 m) and 148.7 (25 m) - Both stations devoid of fauna

Zone colouring


FCR 2.8:1

Less feed wasted, higher digestibilityFCR 2.0:1

Aquaculture Zone 1 – Bolinao Narrows

Impact

Severe

High

Moderate

1

15

75

0 200 400 600 800Scale (m )

N

M odel waste flux - gram s m d-2 -1


FCR 2.8:1


Aquaculture Zone 2 – ??

Impact

Severe

High

Moderate1

15

75

0 200 400 600 800Scale (m )

M odel w aste flux - gram s m d-2 -1

N


1

15

75

0 200 400 600 800Scale (m )


NFCR 2.8:1



Impact

Severe

High

Moderate


FCR 2.8:1 Less feed wasted, higher digestibilityFCR 2.0:1

Aquaculture Zone 4 – 2 rows of 12 large cages

Impact

Severe

High

Moderate

1

15

75

0 200 400 600 800Scale (m )


N

Zone 4 is exposed to waves from the east, so the model will overpredict impact




Impact

Severe

High

Moderate

1

15

75

0 200 400 600 800Scale (m )


N



Aquaculture Zone 6 – Pens

Impact

Severe

High

Moderate1

15

75

0 200 400 600 800Scale (m )


N


Prohibited Aquaculture zones

119.88 119.9 119.92 119.94 119.96 119.98 120

Longitude(E)

16.28

16.29

16.3

16.31

16.32

16.33

16.34

16.35

16.36

16.37

16.38

16.39

16.4

Lat

itu

de(

N)

1

3

5

7

9

11

13

15

17

19

21

23

25

27

29

Reference Vectors(m/s)0.10.30.60.93

Dep

th (

m)

ANDA

BOLINAO

Guigiwanen

CaquiputanStrait

Hr 61

Siapar


Avoiding impact overlap between aqua zones


119.88 119.9 119.92 119.94 119.96 119.98 120

Longitude(E)

16.28

16.29

16.3

16.31

16.32

16.33

16.34

16.35

16.36

16.37

16.38

16.39

16.4

Lat

itu

de(

N)

1

3

5

7

9

11

13

15

17

19

21

23

25

27

29

Reference Vectors(m /s)0.10.30.60.93

Dep

th (

m)

ANDA

BOLINAO

Guigiwanen

CaquiputanStrait

Hr 61

Siapar

1

7

6

3

2

4

Recommended cage culture zones


Recommended cage culture zones

119.88 119.9 119.92 119.94 119.96 119.98 120

Longitude(E)

16.28

16.29

16.3

16.31

16.32

16.33

16.34

16.35

16.36

16.37

16.38

16.39

16.4

Lat

itu

de(

N)

1

3

5

7

9

11

13

15

17

19

21

23

25

27

29

Reference Vectors(m/s)0.10.30.60.93

Dep

th (

m)

ANDA

BOLINAO

Guigiwanen

CaquiputanStrait

Hr 61

Siapar

1

7

6

3

2

4


Zones – what area is impacted

Zone ScenarioArea impacted - % of zone HIGH/SEVERE

SEVERE (% of zone) Rank

1 FCR 2.8 54 6.1 1

2 FCR 2.8 53 6.5 2

3 FCR 2.8 50 9.3 4

4 FCR 2.8 53 20.3 6(Exposed)

5 FCR 2.8 45 13.5 5

6 FCR 2.8 52 7.2 3

1 FCR 2.0 36 0.0

2 FCR 2.0 35 0.0

3 FCR 2.0 36 0.0

4 FCR 2.0 44 5.9 Exposed

5 FCR 2.0 35 0.0

6 FCR 2.0 35 0.0

Zone 4 is exposed and therefore model probably over estimates impact because the model does not take account of waves


Zones – how severe is the impact

Zone Scenario

Average flux in HIGH/SEVERE zone

(g/m2/d) Rank

1.0 FCR 2.8 43 1

2.0 FCR 2.8 44 2

3.0 FCR 2.8 50 4

4.0 FCR 2.8 73 6 (exposed)

5.0 FCR 2.8 58 5

6.0 FCR 2.8 46 3

1.0 FCR 2.0 24

2.0 FCR 2.0 26

3.0 FCR 2.0 29

4.0 FCR 2.0 45

5.0 FCR 2.0 33

6.0 FCR 2.0 30

Zone 4 is exposed and therefore model probably over estimates impact because the model does not take account of waves


Zone Cages Spacing between cages Zone biomass modelled

Average situation with all different fish sizes in zone (EMMA data)

Zone biomass if all

fish 386 grams in all cages

Maximum biomass in zone

1, 2, 3, 5, 6

2 rows of 18 20 m between cages

120 m between rows

137 tonnes 353 tonnes A

4 2 rows of 12

30 m between cages

120 m between rows

277 tonnes 514 tonnes B

Zone 4 cages are large circular cages (20 m diameter* 8m deep)

Zones 1,2,3,5,6, are square cages (12m* 12m*8m deep)

A 386 gram fish require highest feed, 9.8 tonnes per cage *36 = 353 tonnes in zone (square cages)

B 386 gram fish require highest feed, 21.4 tonnes per cage *24 = 514 tonnes in zone (large circular cages)


Scenario – for zone 5 which has the lowest currents, can the zone support a higher biomass if large circular cages are used instead of small square cages?

Large, circular cages versus small, square cages

Scenario Configuration

Area impacted - % of zone

HIGH/SEVERESEVERE

(% of zone)Zone peak biomass

FCR 2.8 2 * 18 square cages 45 13.5 353 tonnes

FCR 2.02 * 18 square cages

(353 tonnes) 35 0.0 353 tonnes

FCR 2.8

FCR 2.0

YES - ? tonnes can be at peak biomass as opposed to 353 tonnes with small cages ( a x % increase)


Overall rank Zone Rank - magnitude of

SEVERE impact

Rank - extent of SEVERE

impact

Rank - depth Rank - current

1 1 1 1 1 3

2 2 2 2 2 2

3 6 3 3 6 1

4 3 4 4 3 4

5 4 6 6 4 5

6 5 5 5 5 6

However, zone 4 is exposed to waves which are not modelled so zone 4 is likely to be more dispersive in reality

Zones ranked in terms of dispersiveness


Summary

TROPOMOD model predicted impact with 2 scenarios, FCR of 2.8:1 and 2.0:1.

Results are for different sized fish throughout the zone, which is realistic, not worse case.

Improvement of FCR of 2.8 to 2.0:1 resulted in:

• reduced feed needed by 29 %

• there was no/little SEVERE impact under cages

• HIGH impact areas were less than 50 % of the total zone area


Recommendations

Zone Cage configuration

Peak biomass

(tonnes)

Spacing

1, 2, 3, 5, 6 2 * 18 square cages

353 20 m between cages, 120 m between rows

4 2 * 12 large circular cages

514 30 m between cages, 120 m between rows

As the deposition footprints extend between 200 and 400 m from the edge of the zone, it is recommended the distance between zones should be a minimum of 600 m.


TROPOMOD has been developed using a similar concept to the following models:

MERAMOD – Sea bass/bream in the Mediterranean – scientifically tested at several sites with sediment traps and benthic fauna sampling

DEPOMOD – Salmon/cod for North Atlantic – used in the Scottish regulatory system to consent farms in Scotland

DEPOMOD and MERAMOD have 100+ users worldwide

Tests with TROPOMOD at Bolinao were satisfactory – the model predicted on average 104 g m-2 d-1, which corresponded to an average value measured in traps of 131 g m-2 d-1 in May 2007.

ECASA toolbox - a tool box of environmental impact and socioeconomic indicators, including descriptions of models and where to find them

www.ecasatoolbox.org.uk

modelling of aquaculture impact and carrying capacity in the philippines using tropomod

Technology

zone zone colourmaintain

feed ration

feed wasted27

feed digestibility49

feed inputbetween

better quality feed

philminaq faeces

allowable zone of effect