Britain traditionally exports most of its catch and is making huge efforts to expand its home market in a bid to try to mitigate the problems with tough export markets.
But despite growing interest in molluscs and crustacea by the British consumer, fishermen fear that it will not be enough to offset the slump in trade abroad.
Jim Partridge, of the Monteum fish company in Shoreham, Sussex, said: "If something doesn't happen soon, I would expect 50 per cent of fishermen and 50 per cent of merchants to go out of business by the end of the year."
Dr Clive Askew, of the Shellfish Association, which represents 400 retailers and fishermen from Scotland to Cornwall, said: "The news we get from around the coast is that it's very serious."
Mr Partridge said the pound had risen so quickly that the margins they built in to absorb such increases were wiped out. Sometimes they were receiving less money than the fish were sold for.
The problem was compounded by the sluggish economies of France and Spain, the biggest markets for shellfish in the past, but whose populations could no longer afford to eat out as often as they once did.
In previous summers, the French would take a lorry-load of crab every day. This year it is one a week. "Europe is completely and utterly dead," Mr Partridge said.
Jeremy Brown, of Just Shellfish in Port Isaac, Cornwall, said prices usually levelled out after Easter at around pounds 9 a kilo for lobster but were now hovering around pounds 6.50 or pounds 7. "We haven't seen prices this low in years and our expenses are the same as ever if not greater," he said.
And despite some optimism in the business about a growth at home, he did not hold out huge hopes for a growth in the home market. "I tried to sell fish door-to-door and there was very little interest. The average housewife is put off by a bone. We don't eat fish or shellfish in Britain," he said.
Yet Dr Askew, from the Shellfish Association, said there were some signs of an interest in seafood, just as British cuisine in general has grown more adventurous in recent years.
"Supermarkets are looking very much more seriously at shellfish - some of it is to do with improving their image as they did by supplying wines." But there would need to be a "huge boost" in Britain offset the drop in exports.
Last year, 116,000 tonnes of shellfish, with a value of nearly pounds 138m, were landed in the UK, an increase of 10,000 tonnes over five years ago. But the amount exported - 71,000 tonnes - has not changed over the same period. British consumers are buying more to eat at home and when they eat out, although much of this is prawns not caught in British waters.
A spokeswoman for Waitrose, often regarded as the trend-spotter in foods, said it had seen a significant increase in interest in shellfish in the last five years. "It's a very large market as far as we're concerned. We have 103 branches out of 115 with fresh fish counters which include shellfish," she said. Stock includes fresh oysters, mussels, scallops and langoustines.
Safeway sells pre-cooked British crabs and British oysters and Marks and Spencer offer prawns and some smallquantities of lobster at its London West End stores.
But fresh fish counters are still a rarity in high street supermarkets, and the number of fishmongers in Britain has declined significantly in recent years.Reuse content