LARGE SCALE VERSUS LOCAL EFFECTS: CHALLENGES PREDICTING E. coli LEVELS IN SHELLFISH

Laurence JONES¹, Shelagh K MALHAM², Helen TAFT², David COOPER¹, Cai LADD², Mathew SEYMOUR²,  David L. JONES², James E. MCDONALD², Peter ROBINS², Lewis LE VAY²

¹ Centre for Ecology and Hydrology, Environment Centre Wales, Deiniol Rd, Bangor LL57 2UW

²University of Bangor, College Road, Bangor, LL57 2DG, UK

e-mail: LJ@ceh.ac.uk

Key words: Active Management Systems; catchment; Combined Sewer Overflows

There is increasing interest in developing Active Management Systems (AMS) for managed shellfisheries where episodic events cause high loadings of E.coli in shellfish, leading to closure of fisheries. Closure of fisheries is required to protect human health but leads to loss of revenue, and can result in loss of confidence in the product. AMS allows the fishery to manage the closure periods more dynamically, closing and re-opening on shorter timescales than are possible under conventional safety testing regimes

However, AMS requires sufficient knowledge of the main factors causing high E.coli loadings, and the processes and timescales over which they operate. We evaluated routine monitoring data of E.coli levels in the flesh of oysters and mussels, from sites around the UK spanning a 12-year period. The aim was to detect the main contributory factors to high E.coli loads. Variables tested included local effects such as proximity to various waste discharge points up to catchment level effects including rainfall, land use, water chemistry and catchment morphology.

Overall we found no single cause of high E.coli levels. At a catchment level high loads were associated with land use and water turbidity, while at a local level they were associated with operation of Combined Sewer Overflows. Significant effects varied between estuaries, and in some cases between shellfish species.