scottish sea farms ltd hunda north biomass and …equivalent treatable biomass of 8398.5 t which is...

SCOTTISH SEA FARMS LTD

HUNDA NORTH BIOMASS AND

TREATMENT MODELLING

TECHNICAL SUMMARY

Report To: Scottish Environment Protection Agency

Report No: 200916-01

Our Ref: RS

Status: V1

Date: 20 September 2016

Scottish Sea Farms Ltd

South Shian

Connel

PA37 1SB

Tel: 01631 574203 Mob: 07825030003

Email: rachel.speirs@scottishseafarms. com

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1. Summary

Modelling was carried out by Scottish Sea Farms Ltd ( SSF) for a proposed new marine cage site

Hunda North. Appropriate maximum biomass, chemical consent limits and sampling stations have

been calculated, consent limits achieved are detailed in the table below:

Treatment Recommended consent mass

Biomass A maximum consent biomass of 1679.7 t and stocking density 17.6

kg/ m³ is recommended for this site.

Salmosan (Azamethiphos) The total quantity of Azamethiphos to be discharged should not

exceed 172.5 g in a 3-hour period or 501.0 g in a 24-hour period.

This can be used to treat one cage in 3 hours or 3 cages in 24

hours at a maximum treatment depth of 2.1 m.

Excis (Cypermethrin) The total quantity of chemical to be discharged in a 3h period

should not exceed 31.2 g. The equivalent treatment volume is

6240 m³

Alphamax (Deltamethrin) The total quantity of chemical to be discharged in a 3h period

should not exceed 11.7 g. The equivalent treatment volume is

5850 m³

SLICE ( Emamectin Benzoate) A maximum treatment quantity ( MTQ) of 587.9 g and a total

allowable quantity (TAQ) of 2939.5 g. This is enough chemical to

treat the maximum biomass 5 times.

Table 1: Consent limits for Biomass and treatment chemicals at Hunda North.

2. Introduction

This document is a technical summary of an assessment carried out for a proposed new marine cage

site located off the north shore of Hunda Island, Scapa Flow. Scottish Sea Farms plan to develop a

site with a cage configuration at this site of 12 x 100 m circumference cages spread over two 2x3 60

m grids. Modelling has been carried out in order to identify appropriate biomass and lice treatment

chemical limits for this new cage configuration. Sampling transects and sampling stations have been

identified and are detailed in section 4 below.

This summary provides site-specific methods only and is supported by generic method statements

AMMR12v01 and AMMR12v02.

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Figure 1: Location of the proposed marine cage site Hunda North, Scapa Flow.

3. Input Data

3.1 Site Data

The input data, including the bathymetry and the current data, for this site was provided by SEPA

and is summarized below:

Site Name: Hunda North

Site NGR: 344318 997579

Receiving Water: Scapa Flow

Company: Scottish Sea Farms

Peak biomass ( tonnes): 1679.7

Medicines applied for: Excis, Salmosan, Alphamax, Slice

Current Meter NGR: 344318 997566

Distance to Shore(km): 0.21

Water Depth at Site(m): 20.5

of Cages: 12

Round/ Square?: Round

Diameter/ Circumference/ Width (m): 100 m circumference

Working Depth (m): 10

Treatment shallowing depth (range?) (m): 2.1

Table 2: Hunda North site data

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3.2 Bathymetry

The model configuration has been modified from the model setup created by Xodus Ltd on behalf of

SSF for the modelling of a proposed new site, Hunda North. The bathymetry was created by

digitizing contours and spot depths from Admiralty Chart No. 35-0 and includes depths collected

during the hydrographic survey, as outlined in report A-30530-S06-REPT-001. The data were limited

to a 1km² model domain with the grid limits:

DataAreaXMin=343820

DataAreaXMax=344820

DataAreaYMin=997090

DataAreaYMax=998090

3.3 Cage set-up

The cage grid consists of 12 x 100 m circumference cages arranged in two groups laid out in two 3x2

60 m grids with a working depth of 10 m. The cage configuration can be seen in figure 2.

Figure 2: Screenshot of cage configuration taken from HundaN- FFMTv3. 0

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3.3 Current data

Current meter data was collected by Xodus Aurora in April 2011 on behalf of Scottish Sea Farms Ltd.

Data was collected using a 600 kHz RDI Workhorse ADCP.

Statistics for this dataset were derived using HGdata_analysis_v7.xls. All data was corrected to grid

north using a Grid Magnetic Angle of 3.16° W. Summaries of the derived statistical data for the 3

bins are available in Appendix 1.

The raw data was formatted into hourly averaged data for use in AUTODEPOMOD using the SEPA

tool temp-20min-HGv3.xls (input data displayed in Table 2). The intermediate Spring tide (SNS) and

Neap tides (NSN) were identified as occurring at hours 196 and 52 respectively.

Site name: Hunda North

Depth at mooring: 26.8

Height of surface meter from bottom (m): 20.06

Height of middle meter from bottom (m): 16.56

Height of bottom meter from bottom (m): 2.06

Number of hourly record at which springs commence: 196

Number of hourly record at which neaps commence: 52

Identify current speed units (m/ s or cm/ s): m/s

Mean Sea Level (mCD): 1.93

Compass variation (deg E/ W): 0.0W

Table2: Input parameters for the SEPA tool HundaN- 20minRS- HGv3

Mean Sea Level (defined as the average of MHWS, MHWN, MLWS and MLWN for St Mary’s (Scapa

Flow)) was derived from Admiralty Total Tide software.

The current velocities at this site were found to be fairly low indicating a quiescent to weakly flushed

site.

3.4 Model set-up

Defaults values were used as described in SEPA guidelines Regulation and Monitoring of Marine

Cage Fish Farming in Scotland Annex H, Methods for Modelling In- feed Anti- parasitics and Benthic

Effects ( issue No. 2.3, 18 May 2005).

Initial runs were carried out using a constant feed input, auto-distribute set to on and an initial

stocking density of 17 kg/m³. All runs used 1 particle initially and were then refined using 10

particles. Passing runs with an ITI of 10 were initially achieved. The simulation was further refined

by carrying out single runs of 10 particles until a passing run with an ITI of 9.9 was achieved.

3.5 Results

A passing run (Run 11) was achieved resulting in a maximum consent biomass of 1679.7 tonnes with

a stocking density of 17.6 kg/m³. Table 3 shows the flux, ITI and area results for this run while a

diagram of the flux contours and deposition footprint can be found in Figure 3. A full summary of

results can be found in the marine sum spreadsheet in Appendix 2. The shape and size of the

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deposition footprint is consistent with the local bathymetry and the direction and strength of the

residual current.

Flux (g/ m²/y) ITI Area (m²)

80% solids 1565 9.9 68308

Cage Area Equivalent 15414 1 27880

Benthic Sampling Area 191.8 30 103897. 1

Table 3: Flux, ITI and Area results for run 11

Figure 3: Diagram of model output for run 11.

Transects have been aligned with the major axis of the deposition footprint (Fig. 3 & 4). The primary

transect has been placed at the point where the 30ITI contour is furthest from the cage group. While

a parallel secondary transect has been included to offer a backup position if required in the field.

Profiles of each transect have been included below in Figure 5.

Sampling stations have been placed along each transect at the 30 ITI boundary and at 10m on either

side.

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Figure 4: Extract from HundaN_ Marine_ Sum indicating position of transects and sampling stations.

Transect 1

Transect 2

Figure 5: Profile of sampling transects for run 11.

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4. Bath Treatments

4.1 Input

The input data for this model is summarised in table 4 below. The hydrographic statistics for this site

were generated using the SEPA tool HGdata_analysis_v7.xls. Distance from shore was measured

from Admiralty Chart No. 35-0 using ArcGIS v10.1.

Loch Data

Loch/ Strait/ Open water : 3

Loch area (km2) : ( only required for Loch)

Loch length (km) : ( only required for Loch)

Distance to head (km) :

Distance to shore (km) : 0.21

Width of Strait (km) : ( only required for Strait)

Average water depth (m) : 20.5

Flushing time (days) :

Cage Data

of cages : 12

Cage shape : 1

Diameter/ Width (m) : 31.8

Working depth (m) : 10

Stocking density (kg/m3) :

Treatment

No. of cages possible to treat in 3

hours :

1.00

Initial Treatment Depth (m) : 2.1

Treatment Depth Reduction Increment

m) :

0.1

Hydrographic data analysis

Mean current speed (m/s) : 0.044

Residual Parallel Component U (m/ s) : 0.016

Residual Normal Component V (m/ s) : 0.002

Tidal Amplitude Parallel Component U

m/s) :

0.070

Tidal Amplitude Normal Component U

m/s) :

0.023

Table 4: Bath Treatment inputs for Hunda North.

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4.2 Results

The consent limits for all Bath treatment chemicals applied for are summarized in the marine sum

spreadsheet which can be found in Appendix 2.

Azamethiphos

Recommended consent mass (3h) – 172.5 g


Treatment Depth – 2.1 m

No. of cages per treatment – 1.0 in 3hrs, 3.0 in 24hrs

The TS plot for Azamethiphos is shown in figure 6 below:

Figure 6: Azamethiphos TS plot

Cypermethrin


No. of cages per treatment – 3.7

Deltamethrin


No. of cages per treatment – 3.5

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5. Infeed Treatments

5.1 Model Set- up

The model was setup using the method described in SSF’ s generic method report Bath and In-Feed

Method Statement and follows the guidelines and model defaults described in SEPA guidelines

Regulation and Monitoring of Marine Cage Fish Farming in Scotland Annex H, Methods for

Modelling In-feed Anti- parasitics and Benthic Effects ( issue No. 2.3, 18 May 2005) unless stated

otherwise below.

The Slice run parameters were set to 5 x maximum biomass (8398.5 t) using an annual feed load of

4291.6 tonnes.

After the initial runs it was deemed necessary to use a blanking file. Single runs of 10 particles were

then used to iterate to a passing (MAX) result.

All other options were set to default.

5.2 Results

The passing run (run 18) for Slice results in a TAQ of emamectin benzoate of 2939.5 g, this has an

equivalent treatable biomass of 8398.5 t which is 5 x peak biomass. The MTQ is 587.9 g, this is

enough to treat the maximum consented biomass of 1679.7 t in one treatment. This scenario results

in a mass balance is 2101 g and a mean near-field concentration of 294.7 gkg¹. The near-field

concentration levels exceed the EQS trigger value with a difference in concentration between

predicted near field residue concentrations and EQS values of 287 gkg¹.

Far-field error – We are aware that due to the 120 m gap between the cage groups the resulting

overlap has led to an over calculation of the far-field area. As this error has not prevented the model

from running to an EQS compliant scenario it has not been included in this report. However the

correct far-field area has been calculated as ~172591 m². The far-field area of impact is predicted to

be 143946 m2 at the TAQ.

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Figure 7: Diagram of model output from Slice Run 18 including blanking file.

6. Discussion

The footprint of deposition produced by the model is consistent with the bathymetry and current

data recorded at this site. This is also reflected by the volume of mass retained within the model (99

of the mass released).

There is little to no export from the model grid with dispersion of material almost completely within

the deposition footprint.

Hunda North is characterized by bathymetry which follows the contours of the coastline with no

unusual features and a comparatively simple hydrography. This implies that the short term and MLA

bath treatment models adequately simulate the behaviour of bath treatment chemicals released at

this site.

The maximum consent mass for Slice at Hunda North has been calculated as 2939.5 g, enough to

treat a biomass of 8398.5 t. The MTQ is 587.9 g which is sufficient to treat 1679.7 t.

The EMBZ mass balance for the passing run (118 days) is 2101 g, this is the mass of medicine residue

which is left in the model grid at the end of this run. In order to calculate the amount of medicine

lost from the model due to export the following equation is used:

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2939.5 x 0.74) - 2101

74.23 g

Therefore around 2.5 % of the medicine released is exported from the model grid. This is consistent

with the relatively low current speeds and weak residual current found at this site. The model shows

that the vas majority of the Slice residue is retained within the model grid.

Using the SEPA tool marine_sum.v3.1 we can see that the overall affected area is likely to cover an

area of 0.8 km². This is less than 10 % of the available receiving area of 10 km².

7. Conclusion

The recommended consent limit for this site is a maximum biomass of 1679.7 tonnes at a stocking

density of 17.6 kg/m³.

The model output for this site is representative of a quiescent/ weakly flushed site with a deposition

footprint consistent with the relatively weak vector averaged residual current and uniform

bathymetry of the site.

The recommended chemical consent limits for this site are:

Azamethiphos - 3h hour recommended consent limit of 172.5 g and a 24h limit of 501.0 g. This

quantity is sufficient to treat one whole cage with a treatment depth of 2.1 m in 3hrs and 3 cages in

24hrs. In order to treat the whole site four treatments of three cages over four days would be

required.

Cypermethrin – 3h recommended consent limit of 31.2 g; this is sufficient to treat a volume of

6240.0 m³, or 3 whole cages at a shallowing depth 2.1 m.

Deltamethrin - 3h recommended consent limit of 11.7 g, this is sufficient to treat a volume of 5850

m³ or 3 whole cages at a shallowing depth of 2.1 m.

Slice – A recommended consent limit of 587.9 g (MTQ) and a TAQ of 2939.5 g. This is enough

chemical to treat the maximum biomass 5 times.

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8. References

SEPA (2006) In-Feed consent limits at dispersive sites – v3. Available online:

http:// www.sepa.org.uk/water/ water_regulation/ regimes/ aquaculture/ marine_aquaculture/ modell

ing/ technical_guidance_notes.aspx#limits

SEPA (2005) Regulation and Monitoring of Marine Cage Fish Farming in Scotland Annex H, Methods

for Modelling In-feed Anti- parasitics and Benthic Effects ( issue No. 2.3, 18 May 2005). Available

online:

http:// www.sepa.org.uk/water/ water_regulation/ regimes/ aquaculture/ marine_aquaculture/ modell

ing.aspx

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Appendix 1 – Current Meter Data Summaries

Sub- Surface

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Cage Bottom

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Near Bottom

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Appendix 2 - Marine Sum Spreadsheet

scottish sea farms ltd hunda north biomass and …equivalent treatable biomass of 8398.5 t which is...

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