"You have to be rich or famous to eat one of these," says Les Angel, hauling a full dredge of oysters on to the deck of The Three Sisters, "but I'm not either."

Known around Falmouth as the only oysterman who doesn't eat his catch, Les has been working the beds of the Carrick Roads and Truro River for almost 40 years. He is part of a family tradition that stretches back far further and this year he has been joined by his son, Daniel.

Powered solely by the wind, the Cornish crews operate the only oyster fishery under sail in the whole of Europe – and perhaps the world. In order to protect the natural ecology of the riverbeds and oyster stocks, the men are governed by strict and ancient rules which permit them to work only from October 1 to March 31. Their hours are also restricted: 9am to 5pm from Monday to Friday, 9am to 1pm on Saturdays and absolutely no working on the Sabbath.

Six boats, each equipped with primitive hand-pulled dredges, were plying an area of the Truro Oyster Fishery just off Mylor on the first day of the season. Heavy rain made visibility difficult, but these men are used to such discomforts.

"It can be torture sometimes, but you still enjoy it," said Daniel, who also works on supply boats out of Falmouth. "It's better when it doesn't rain."

While agreeing that it can be hard graft, his father says that being your own boss and having your own boat makes up for any drawbacks.

"I've known days in January when we have been dredging in a row boat and working in T-shirts, then other times it's bouncing four feet up and down before you leave the harbour and the waves are pushing water right across the deck," he said.

"But it's been pretty good today, with a just enough weight on the sails to pull the dredges along. We're getting a reasonable catch and should land about 80 kilos today. The oysters are a nice size too — and you can't get any better oysters than these."

Native oysters from the Truro Oyster Fishery are definitely prized by foodies throughout the UK. Les refused to be drawn on precisely how much he is likely to make for one of these strangely-desirable bivalve molluscs, but it is certain to be a fraction of the £35 a dozen charged by Bentleys, a swish London seafood bar where many of them end up. It's a far cry from the days of Les's forebears, when oysters were regarded as simply part of a subsistence diet.

It's easy to conjure those days in the mind's eye, through the driving rain and poor visibility aboard The Three Sisters. A little way to starboard, Tim Vinnicombe is working the Boy Willie, a gaff-rigged cutter built in 1865 and owned by his family since 1923. A little further off, in the direction of Restronguet, Jonathon Bailey is hauling a dredge on to Katrina, an elegantly-lined vessel built in Looe around 1913. And not far away are Dolly, Alf Smythers and Ada, another old-timer, built locally in 1870.

Tim Vinnicombe, whose family has been involved with the oyster trade for five generations, has been joined this season by newcomer Gordon Howells.

"With me it's about the generations, the tradition, knowing our family has been a part of it for all this time," said Tim. "But it's also a very valuable source of work and income, especially during the winter months when there's not a lot you can do outside the estuary."

Easing red sheets through a forest of steel masts or drifting towards the estuary mouth on an outgoing tide against a strong southerly wind, while hauling a heavy dredge, requires immense skill and a cool head — yet these men respond instinctively to each change in the conditions. And as well as the physical presence of the boats themselves and the family names of those who operate them, history is preserved in the language used by the men. Words like culch, culch tray, cul-tac and culling are unique to their industry.

"Culch" refers to the contents of a dredge, the mess of seaweed, crabs, stones, queen scallops, starfish, oysters and anything else dragged from the seabed. The "culch tray" is where it is tipped to be "culled" (or sorted), while a "cul-tac" is a small knife use to trim shells and dispatch predators. It might reasonably be assumed that all these terms are originally derived from the Cornish language or from Cornish dialect, but it seems they were brought to here by East Anglian oystermen sometime during the 19th century.

And it's not only oysters that end up in the culch tray.

"I've found all sorts," says Les. "Wallets, watches, compasses, sunglasses. You name it and it comes up in the dredge. We even found a cannonball once and last year I pulled up an outboard engine."

The boats' home port of Mylor is packed with pleasure boats these days. Gleaming yachts lie alongside grubby wooden punts that have seen better days. It's an odd relationship; the marina could accommodate double the number of pleasure craft – a lucrative business and steady employer – but such a move could have an adverse effect on the livelihoods of a dozen or so oystermen. It is a issue close to the heart of oyster bailiff Paul Ferris, whose job is policing the Truro River's fragile fishery and ensuring the environment is protected. Having worked the beds himself, he knows from personal experience just how precarious an occupation it can be.

"My grandfather and great-grandfather were oystermen and the work has changed little since their day," he says. "People may wonder why these men continue to do it and my only answer is that there's just something about it, something indefinable. It's a very small industry and requires a specific set of skills. For most of these men these skills have been handed down through the generations.

"There have been six boats out for the first day of fishing, and perhaps three or four more tied up and waiting to hear how it went before deciding whether to buy a licence for the season."

A licence is issued per dredge and this allows the operator to work the beds only from October 1 to March 31. As well as the sailing cutters, which range in length from 20ft to 42ft, a number of oystermen operate dredges from rowing boats. This involves an arduous routine of anchoring the punt, rowing against the tide, launching a dredge, drifting back to anchor and lifting the dredge, before repeating the whole process.

Les, Daniel, Tim, Jonathon, Gordon and the others will be working flat-out over the next week or so to ensure an abundance of oysters is available for the 14th annual Falmouth Oyster Festival, which takes place from October 14 to 17. As well as sampling the fruits of the sea there will be a Falmouth Working Boat on display, a film about the history of the fishery, cookery demonstrations, live music, Walter Hicks' wines, Skinner's ale and a range of food stands offering everything from grilled mackerel to chocolate crepes.

Les Angel and Tim Vinnicombe's brother Marshall will be running the popular oyster bar during the event as part of the contribution made by St Michael's Hotel.

Les won't be tempted to sample the fare, of course, and while he may say it's the price that puts him off, the truth is he's just not partial to that distinctive rock-pool flavour. It's his choice, but it doesn't stop colleagues ragging him on occasion. And it's not as if he hasn't tried. There is a legend doing the rounds in Falmouth that tells of a swish buffet attended by several oysterman, during which Les was goaded into swallowing a raw oyster straight from the shell in the time-honoured fashion. He tried once, he tried twice and on the third attempt down went the mollusc... only to reappear seconds later back in its shell. It is said that initial cheers turned to groans of disgust.

But Les had the last laugh. Some minutes later, a man who can only be described as a squiffy toff sailed by the table and, noticing a lone oyster on the buffet, remarked: "Oh, you've left one. May I?" Before anyone could stop him, the tipsy gourmand had popped the well-travelled and pre-digested morsel into his own mouth.

"Divine!" he remarked.