'The UK doesn't have that same investment,' she says. Dr Philine zu Ermgassen, researching oyster restoration with the Nature Conservancy, points to the US where public funds are helping to relay oyster beds, and reaping the benefits that come with the return of these important habitats (they're critical for juvenile fish, for instance). Should we be eating natives at all? Absolutely, say scientists, who gathered at a conference at St Catharine's College, Cambridge last month. There are periodic bans in certain areas, such as that agreed this summer between the Blackwater Oystermen's Association and the Essex Wildlife Trust, after the population there was found to be close to collapse. Natives are in trouble in parts of the country – a combination of overfishing, pollution and disease has contributed to their decline (in a global assessment, scientists estimated UK stocks had dropped by between 90% and 99%). Native oysters were once abundant in Britain, but today you are more likely to come across hardier faster growing rock – or Pacific – oysters, which have the commercial advantage of being available all year rather than just in the September to April native season. Cornwall's geology gives the oysters a distinct, slightly coppery flavour – they are being considered for protected designation of origin status. He charges around £1.25 for the smallest – grade three (67mm) – to £3.50 for larger specimens, selling online, to local restaurants such as the Greenbank and the likes of Mark Hix in London. The short season and dwindling catches mean it is a far from lucrative business – bad weather meant Ranger got only 50 days fishing last year, catching about 50 oysters a day.

'You want to catch more, and sail less, go across the seabed slowly.' A lot of the skill is in the sailing, he says. At 37, Christopher Ranger is the youngest owner/skipper unusually, he has taken on an apprentice and is teaching him the ropes. But this could be the last generation of oystermen here – numbers have dropped to 10 boats with around 20 fishermen earning a living. It is a public fishery, open to anyone with a licence, and several families have worked it for decades.

This is probably the last oyster fishery in the world using such traditional methods – only vessels powered by sail or oar can operate, within restricted hours – which makes for a sustainable operation.

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