Herpes virus which kills oysters found in River Exe for first time

A potentially lethal herpes virus which affects Pacific oysters has been found in a Devon river for the first time.

The government confirmed it had declared a new "containment area" covering the tidal waters and coastal zone around the River Exe.

The Fish Inspectorate said the virus poses no risk to humans or other marine creatures.

Chris Evans, head of the Fish Health Inspectorate, said they took samples from the affected area in August which tested positive for the oyster herpesvirus-1 microvariant.

He said they visited the river after a shellfish farmer noticed "unusual mortalities" in Pacific oysters.

The "containment area," which has been issued under the Aquatic Animal Health Regulations, restricts the movement of Pacific oysters.

Farmers can still move the oysters out of the disease zone but only if they've applied to the Fish Health Inspectorate for permission.

"Oyster herpes-virus is a virulent viral disease of the Pacific oyster, and is spread primarily through the movement of infected oyster," Mr Evans said.

"It is important that the disease is contained to prevent its spread to other oyster growing areas in the UK."

Pacific oysters are the most important species of oyster farmed in the UK both in terms of volume and value.

Mr Evans said previous outbreaks of the virus have resulted in "upwards of 90% mortality" and have "devastated" Pacific oyster populations in France, Jersey, Ireland and parts of England.

He added: "We don't know yet what the impact will be, but it has the potential to impact farmers who could lose a significant amount of stock leading to economic damage."

Once an area is defined as a "containment zone," it remains in place "long-term to contain the virus in infected areas," he said.

Disease control zones are currently in place in a number of Pacific oyster farms in England, including in Kent, Essex, Suffolk and Poole Harbour.

He confirmed that it is the first time the virus has been recorded in the River Exe, but that a "containment zone" has been in place in the River Teign since 2015.

Martin Syvret, who runs the consultancy Aquafish Solutions, is establishing a pilot Pacific oyster farm within the affected area on the River Exe.

"Once you've got the disease, you have to learn to live with it," he said.

"This means changing how you farm the oysters and using different techniques, for example by trying not to handle them too much or putting them in deeper, colder water."

He added: "It's not all bad news. The realistic implications are that you take an initial financial hit, but if you can recover from that, learn to adapt your practices and live with the virus, you could potentially have economic gains as well.

He said that farmers can eventually be "better off" as they can start buying seed from areas which already have oyster herpes virus, such as France.

"The reality is that the French have a bigger industry, which means they can produce oysters much more cheaply and you can then buy seed considerably cheaper," he said.

"The EU, and France in particular, is putting a lot of research, time and money into developing oysters which are resistant to the disease so effectively you're buying cheaper seed that as time goes on is likely to be more resistant."