Report No SR4018



Dec 1995


Until recently, the farming of salmonids in cage farm operations in freshwater and marine waters has been expanding rapidly both in terms of the tonnage of fish produced and the number and size of farms. This rapid increase in the growth of marine and freshwater caged fish farming in recent years is a cause of concern for the regulatory authorities in Scotland and Northern Ireland.

The RPAs in Scotland have employed a number of techniques to assess the impact of fish farming on sediments. Recently, ADRIS approved a report by its Technical Group on Monitoring Cage Fish Farms (ADRIS, 1993) which laid out a framework of Environmental Quality Objectives (EQOs) and Environmental Quality Standards (EQSs) pertaining to cage fish farming and made recommendations for monitoring depending on the size of the fish farm.

As part of the 1993/4 research programme SNIFFER commissioned a scoping study to establish the range of techniques and strategies employed in the UK and overseas to monitor the effects of organic enrichment, in general, and under cage fish farms, in particular. Then, using information from the review and that already available to the ADRIS Technical Group, to propose and cost a field study aimed at providing the information to develop protocols and EQSs, where appropriate, for the recommended techniques of sediment monitoring.

From information gained from an extensive literature search and consultation exercise, it has been possible to identify a range of techniques used to detect impacts on the sediments. These have been classified as physical, physico-chemical, chemical, biological and ecotoxicological. A wider range of techniques has been applied to marine waters than freshwaters. However, a core of essentially comparable techniques has been found to be used most successfully and most often. These are direct observation of the bottom sediments, analysis of samples for sediment chemistry and benthic infauna

Direct observation of the sediments can be undertaken using either suitably trained divers or by video/photographic techniques. Such techniques can identify the depth and spatial extent of any organic accumulation (e.g. waste feed and blackened sulphidic sediments) and the presence of white filamentous bacteria (Beggiatoa). Analysis of samples for sediment chemistry includes parameters such as organic carbon, total nitrogen, total phosphorus and contaminants such as zinc and copper and antibacterial agents. Analysis of samples for the benthic infauna provides a direct and ecologically relevant measure of environmental impact and the response of the benthic communities to organic enrichment is well described. Each of these techniques provide end-points that offer potential for EQS development. The recommended field study has been fully scoped with respect to the techniques to be included, the sampling strategy, the sampling and analytical protocols and the cost. Three options have been identified corresponding to ways in which the recommended field study might be funded.

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