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Marine aquaculture modelling

Computer modelling is used as a guide to determining licensed discharge quantities of anti-parasitic chemicals and organic waste arising from marine fish-farm operations.

The modelling tools promoted by SEPA provide robust predictions in most cases, requiring relatively little site-specific information. Nevertheless, the quality of the model outputs is dependent upon good quality data and careful implementation of the models and interpretation of their results.

This page provides access to a variety of software tools, and reference and guidance materials.

Survey and modelling manuals

This section introduces the parts of SEPA's fish farm manual that relate specifically to data collection and modelling.

Site-specific data

The robustness of the modelling is highly dependent upon the quality of the data that is used. Both SEPA and SAMS (Scottish Association for Marine Science) promote the collection of the most representative data possible. We encourage applicants to submit high quality data that exceed the existing minimum requirements. Due to improvements in equipment, and the importance of these data, SEPA now require that all new hydrographic data recorded should have a component that is measured at a maximum of 3m above the seabed.

Attachment VIII (226k) - Site and Hydrographic Survey Requirements

Minimising the impact of sea-lice treatment chemicals and of solid organic waste

Sea-lice are a natural parasite of salmon; in the wild, salmon's migratory lifestyle means that they only come into contact with lice sporadically, and are hence unlikely to develop an imperilling lice burden. Conversely, caged salmon are unable to evade their parasites, so farm managers use a range of anti-parasitic chemicals to protect their stock. There are two predominant modes of treatment:

  1. a topical 'bath' treatment, where the water in which the salmon swim is dosed, and the chemical concentration is maintained for a prescribed period; typically, this entails reducing the volume of a cage by lifting the base of the nets, enclosing it in tarpaulin to create a 'bath', and maintaining the dosed volume for one hour;
  2. an in-feed treatment, where the stock are fed a precise dose of pelletized feed impregnated with the anti-parasitic chemical, typically daily over a period of a week.

Bath treatments result in a release of the treatment chemical in solution when the tarpaulins are removed, creating a surface plume that gradually disperses as it is carried away from the site on the tide. In-feed treatments result in a release of the treatment chemical bound to solid material, due both to uneaten feed pellets falling to the seabed, and to faecal material, as the ingested chemical is gradually excreted. The physical processes that determine the concentration of the chemicals in the environment over time, and their eventual fate, are different for the two treatment types, so different modelling tools are used for each.

The ongoing release of solid organic material during normal farm operations, in the form of waste feed and of fish faeces, has the potential to have a damaging impact on the seabed. This impact is assessed with the same modelling tool as in-feed chemicals because the same physical processes govern it. The two modelling approaches are described in the following annexes to the Fish-farm Manual:

Fish Farm Manual Annex G (300k) – Models for assessing the use of medicines in bath treatments

Fish Farm Manual Annex H (2.08mb) - Methods for Modelling In-feed Anti-parasitics and Benthic effects


Chemical modelling

Presentations from a seminar explaining the modelling tools used for predicting the impacts of bath and in-feed treatments are listed below.

Biomass modelling

A workshop was held in March 2005 to herald the introduction of the new approach to setting site biomass limits from modelled benthic impact due to organic wastes, and of the associated additional functionality in the AutoDEPOMOD modelling tool. The material and exercises presented have subsequently been developed for the AutoDEPOMOD training courses that have been run periodically by the model's primary author, Chris Cromey.

Data analysis, modelling, and reporting tools

Current meter and wind data analysis

SEPA has produced a MS-Excel workbook that facilitates the analysis and reporting of current meter and wind data.

In addition to the in-built instructions and cell notes, some further usage notes are available in a technical guidance note

Bath treatment models

The bath treatment model as described in Annex G to the Fish-farm Manual is available as an MS-Excel workbook:

Gillibrand and Turrell's paper describing the long-term model is available from the Scottish Government website: Gillibrand & Turrell, 1999

In-feed and biomass models

AutoDEPOMOD is a development of the DEPOMOD aquaculture impact model that integrates site configuration, load scenario iteration, results visualisation, and EQS testing tools into a single package. It has been developed by the Scottish Association for Marine Science (SAMS) in conjunction with SEPA and industry partners.

To use AutoDEPOMOD, it is also necessary to install the Microsoft Excel spreadsheet program and Golden Software's Surfer contouring program (either v.7 or v.8).

Users are advised to check that they have the following most recent versions of the program executables installed:

  • autodepomod_srf7.exe - version 2.0.51 (22/04/05)
  • autodepomod_srf8.exe - version 2.0.52 (17/08/05)

NB: the version number and compilation date may be found either in the title bar of the user interface, or on the 'Version' tab of the file properties, obtained by right-clicking the executable file icon and selecting 'Properties'.

Modelling results summary

Current data summary statistics and the results of the biomass and chemical modelling are reported using a MS-Excel workbook template.

Download Marine sum v3.xls (106k - version 3.2)

NB: No hard copy of the Marine Summary workbook is required as part of an application; however, an electronic copy of this is essential.

Both the 'chemical' and 'biomass' sheets incorporate a calculation of the minimum area required to disperse exported material to the far-field EQS concentration. Importantly, the workbook invites the modeller to provide an estimate of the available area downstream – with respect to the near-bed residual current direction of the farm site - over which any exported carbon or in-feed chemicals may be distributed. This is included to give the applicant a better idea of the relationship between the required distribution area with respect to exported material and the distribution area available to the site.

Additional technical guidance

Over time, as an increasing number of sites have been modelled, a variety of more complex scenarios have been confronted and tackled, and certain limitations of the modelling tools have been identified and, often, addressed. This has resulted in a number of guidance notes being issued, certain of which will be incorporated into revisions of the 'Fish-farm Manual' documents when these are reviewed.

Modelling methods reports and 'test site' results submissions

Modelling predictions form part of the supporting information accompanying a CAR application, for which the applicant is legally responsible; information that is entered onto the Public Register must meet certain scientific and reporting standards. To reduce the amount of information required for each application, SEPA promotes a scheme whereby a modelling practitioner, who intends to undertake modelling for many sites, need only submit a single copy of their modelling method. This is held as 'Environmental Information' on the Public Register and referenced in any further modelling results submissions.

The modelling produces license limit recommendations, and throughout the process any errors generate an environmental risk. To give the modeller, their client, and SEPA some basic confidence that the modelling techniques and tools are understood, SEPA requires that standard demonstration sites are modelled and reported. This gives the modellers an opportunity to produce a valid report template, and makes it easier for SEPA to identify any errors in the modelling process.

Submitting data and modelling results

In order to offer applicants a consistent and efficient service, SEPA requires an electronic copy of all raw, extracted, and processed data, site survey and hydrographic data reports, and modelling reports. Ideally, these reports should be in PDF format, with 'Content Copying or Extraction' set to 'Allowed'; this enables the reviewing and feedback process. The raw data, modelling files, reports, and an electronic copy of the Marine Summary MS-Excel workbook should be submitted on a CD.

Please include only the files relevant to final compliant model runs; AutoDEPOMOD v2 includes the facility to delete failing model runs automatically.

Pre-application process

The information supporting a CAR application has to be checked before the application is considered valid. To reduce the likelihood of an application being rejected due to insufficient or inadequate scientific information, SEPA promotes the phased submission of data and reports prior to making an application.

Read about the pre-application process for fish farms (21k)

Application CD

Apart from signed copies of the application forms, the entire application and its supporting information can be submitted electronically, on CD. If SEPA's favoured pre-application process is followed, a single application CD will be populated in stages. It is advisable to construct the skeleton directory structure for the various pieces of information at the outset, as this helps to reduce omission or repetition of the required information.

External links

Position fixing, bearings and projection conversions

Read about position-fixing using the national GPS network.

The grid convergence angle (for correcting bearings to True North) at any specified location may be obtained with a useful facility, amongst other transformations between projections, within the free spreadsheet tool available from the national GPS website.

Further information about conversions between Magnetic, Grid, and True North may be found on the Ordnance Survey website

A freeware OSTN02 converter (Grid InQuest) for converting between positions recorded by longitude and latitude and the National Grid references (NGR) is available from Quest Geo Solutions Ltd.

Software for modelling

Distribution and technical support for DEPOMOD and AutoDEPOMOD is provided by Chris Cromey of Map and Marine Ltd on behalf of the Scottish Association for Marine Science.

The contouring software package, Surfer, is produced by Golden software and marketed in the UK by GeoMEM.

Electronic charting software and licensing of electronic Admiralty chart data may be discussed with SeaZone Ltd.