Carrying and assimilative capacity of theenvironment is fundamental to the extent towhich aquaculture can develop sustainably, writes Mark James, FRM Ltd, in a CEFAS Shellfish News publication.

Carrying capacity

Research in this area is ongoing and will help to optimise the balance between fish and shellfish cultivation in sea lochs. Although a number of carrying capacity models have been developed including those to optimise production at farm level for long line mussel culture for example, developing models to predict assimilative capacity at the sea loch scale has been difficult.

Existing models are costly to set up and implement, but under project SARF012 a pragmatic approach has been adopted which uses available environmental and hydrographic data to predict changes in key nutrients and their impact on phytoplankton populations as a result of increasing fish farm production tonnages. Under an ongoing project, SARF012a, this approach to modelling assimilative capacity is being validated against a number of representative Scottish sea lochs and extended to include a shellfish component, which will address the carrying capacity side of the equation at the loch scale. The results of this two year project should provide the tools required for both the industry and regulators to make objective decisions about the scale and mix of aquaculture activity that takes place in any given sea loch.

Marine Bills north and south of the border, coupled to fundamental changes to both planning regulation and process may have a profound effect on aquaculture in our coastal waters. However, whilst the legislation that flows from these initiatives are “enabling”, the basic information required to apply it on the ground is often lacking.

Environmental issues

Environmental Impact Assessment (EIA) has long been a feature of fish farming, but it is becoming clear that some shellfish cultivation activities may be included in such requirements in the future. However, “impact”, its significance and ultimately the threshold criteria or values that are set to determine it, are difficult to define and may historically have been set as an expedient rather than a scientifically defendable measure.

A review of Environmental Quality Standards that underpins many aspects of EIA’s and feeds into the development of carrying and assimilative capacity models has been conducted (Project SARF011). A project to assess appropriate thresholds for the potential triggers for Environmental Impact Assessments (EIA) for shellfish farms has also been conducted (Project SARF031). The latter meeting some stiff resistance from shellfish farmers fundamentally opposed to the potential introduction of EIA’s for shellfish farming developments.

Recent and impending changes to planning regulation and processes have also stimulated research to review fish farm EIA’s (SARF024) and thresholds (SARF040).

This work has already contributed to the development of templates designed to streamline and focus the scope and conduct of EIA’s. This work will undoubtedly contain valuable pointers to areas that may be relevant to shellfish cultivation.


Legislation and regulation can inevitably lead to increased costs and whilst such “costs” will form part of a regulatory impact assessment put before Ministers when they consider new legislation, the wider social and economic impacts are rarely considered in any depth. Project SARF046, is assessing the potential socio-economic impacts of new and amended legislation on the cultivation of fish and shellfish species of current commercial importance.


We are all becoming more aware of the need to minimise and manage our waste, as this constitutes a direct and tangible reference of sustainability. Project SARF037 has provided a strategic and detailed review of the current status and future options for waste management and minimisation in the aquaculture sector.

Water quality

Real and perceived declines in water quality, coupled to somewhat incomparable testing standards used by different regulators led for a calls for a research project in Scotland to take a comprehensive look at the underlying reasons for periodic declines in water quality. Project SARF013 undertook a detailed sanitary survey together with a GIS catchment mapping. Through assessment of historic data and weather patterns intensive sampling regimes were undertaken to provide a time-line for contamination events with comparative testing of E.coli, using the FSA approved method, Faecal coliforms using the approved SEPA method together with bacteriophage and norovirus testing. A supplementary project was also commissioned to determine bacterial fluxes arising from a range of inflows – both “natural” and domestic.

This comprehensive study has revealed some very interesting results – at the start of the project, the finger of suspicion was clearly pointed at what was perceived to be inadequate sewerage provision and or “unmanageable” diffuse pollution resulting from run off from land associated with local hill farms and deer populations.

The results revealed that high bacterial loads followed heavy rainfall after periods of two to three weeks of dry weather. The duration of subsequent shellfish contamination with E.coli was generally a few days. The incidence of viral contamination of shellfish in the study area was very low which fits with relatively low human population density and recent upgrades in the local sewerage system. The use of bacterial flux measurements proved to be a highly cost effective way of apportioning the sources of bacterial contamination and led to the discovery that three relatively small streams were significant sources of the total bacterial load flowing into the study area. Further investigation suggested that hard standing used by cattle, drained directly into the streams. As a result of this discovery, the Scottish Environment Protection Agency has taken action to ensure that the drainage problems are rectified.

The conduct of the sanitary survey also proved to be an illuminating experience. One assumes that in this age of electronic information that “someone” knows where all our domestic sewage goes. Not so! The lack of any centralised and accurate records meant that the research team eventually had to resort to walking the shores of the study area, noting the position of outfalls and dwellings and contacting their owners directly – many of whom had no idea of whether they were on private or local authority sewage systems! This does not bode well for the more general requirement to conduct sanitary surveys in shellfish harvesting areas.

Research of this kind is often technically and logistically challenging, the inevitable tension between the requirements of regulation set against the commercial livelihoods of local shellfish farmers and the multimillion pound interests of a large water company gave this project additional but important facets – that ultimately yielded important results.

As with many applied research projects, the process of conducting the project and getting all key players around the table can lead to significant progress that goes beyond satisfying “scientific” objectives. Developing a mutual understanding of the problems faced by all parties, often through basic discussion of how a sample is taken, stored and processed for example, can be very productive. Sustainability is based on understanding – not unfounded and convenient assumptions!


An important international aquaculture symposium will take place in Edinburgh on 21st and 22nd April 2009. The Scottish Aquaculture Research Forum (SARF) in association with the Royal Society of Edinburgh and the Norwegian Academy of Science and Letters is staging the event to bring together a range of international experts to address some of the key issues underpinning the sustainability of aquaculture. Whilst the event will focus on Scottish and Norwegian experience, the programme of presentations will have clear resonance with the way that aquaculture is conducted elsewhere in Europe and beyond.

A range of 34 invited speakers will address the themes of: Understanding our Environment; Science into Policy and Regulation; Fish health and welfare; and Sustainability. The Symposium programme is designed to deliver a coordinated series of presentations to meet the needs of delegates from a broad spectrum of specialist and non-specialist backgrounds.

February 2009

the Fish Site Editor

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