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Shellfish Monitoring

Cornwall Port Health Authorities responsibilities include the classification of the shellfish beds under the EC Hygiene Directive. The risk to humans of consuming shellfish (usually either raw or lightly cooked) has been well documented for decades. Large outbreaks of food poisoning and typhoid still occur worldwide where shellfish have been gathered from polluted estuaries. In order to prevent this the EU produced a Directive some 10 years ago which has subsequently been implemented in Member States by individual Regulations. The Directive called for monthly sampling of all live bivalve (eg oysters, mussels and cockles) production areas so that the water could be categorised A, B, C or prohibited, according to pollution levels. To read more on how beds are classified in the UK please visit the CEFAS website

The majority of beds locally which come under control of this Authority are Class B which means that the shellfish have to be purified in clean seawater for at least 42 hours before being marketed for human consumption. Shellfish from Class C beds must be relaid at approved sites for at least 2 months. You can check the check the local classification status of beds under this Authority. 

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Shellfish harvesting areas may be downgraded from A to B or from B to C due to high levels of toxins discovered during routine sampling. This is often only a temporary measure introduced until such time as the water quality recovers to its normal levels. Occasionally, shellfish beds may be upgraded from C to B or from B to A if the water quality in that particular area has shown very low levels of bacteria over a specified period of time. 

Gatherers of live shellfish are required to complete Movement Documents, issued free of charge by this Authority, when shellfish are taken from their beds. To be issued movement documents please email

Another considerable burden on the Authority's resources is the regular sampling of shellfish and seawater to monitor the prevalence of biotoxins.  Biotoxins are produced by certain marine algae and accumulate in the flesh of shellfish which filter feed upon the algae. Certain concentrations of toxins (depending on the specific biotoxin) can be lethal. Relaying and cooking shellfish does not reduce the toxin levels and so consumption of toxic shellfish during an algal bloom has to be avoided. The Authority publishes an annual sampling programme for both classification sampling work and marine biotoxin monitoring. 

Annual sampling plans are published by CEFAS (Centre for Environment, Fisheries and Aquaculture Science).