Marine experts say we will soon have to get used to eating hake, mullet and other species as coastal waters heat up

Cod and chips could soon become a dish of the past, as Britain's waters become ever warmer. Marine experts have warned that rising sea temperatures are transforming the makeup of fish stocks in our coastal waters.

Where cod and haddock once thrived, sea bass, hake, red mullet and anchovies are now being caught in rising numbers. If Britain wants sustainable fisheries round its shores, it will have to turn to these for the fish suppers of the future, they add.

"We are going to have to be much more flexible about the fish we eat as our coastal waters continue to warm," said Professor Richard Lampitt of the National Oceanography Centre, Southampton.

"The idea that the cod is the only fish worth eating is part of a mindset that we can no longer support."

Marine scientists have found that the seas round the UK have risen in temperature by a remarkable 1.6C since 1980, a jump that is almost four times the global average rise for ocean temperatures. Britain's position on the relatively shallow continental shelf of Europe, and the enclosed nature of our seas – the North and Irish seas and the Channel – have intensified the impact of global warming.

As a result, our waters are now attracting more and more unexpected visitors, including dolphins and a pair of humpback whales – a rarity for UK waters – that were seen in the Irish Sea last month. Other changes have been even more profound. "Over the last 35 years, 15 of the 36 species surveyed in the North Sea have shifted latitudes," said oceanographer Professor Callum Roberts of York University. "The average shift was 300km north."

Cold-loving fish have moved north towards Iceland and the Faroe Isles while warm-water fish have moved up from the south to take their place, added Roberts. Cod is now hardly found in our waters, for example, while the John Dory, a narrow-bodied fish with a long, thin jaw that was once found only near the south-west tip of England, has colonised the North Sea as far as Scotland.

"The trouble is that our national appetite for fish is still monopolised by the 'big five': cod, haddock, tuna, prawns and salmon," said Professor Stephen Simpson of Exeter University. "But very few of these are caught in our waters. So we have to import them – cod from Iceland, tuna from the tropics, for example – or they are grown on fish farms, like the salmon. Only haddock survives in some northern UK waters."

At the same time, however, stocks of gurnard, sea bass, John Dory, ling, hake, sardines and other fish are spreading from the south into British coastal waters. "Unfortunately, UK fishermen who are bringing them in cannot find any market for their catches in the UK.

"As a result they having to sell them to Spain and other European countries," said Simpson.

"We should be eating these fish. They come from our waters today and if we ate them instead of cod we would no longer have to import so much fish. But we won't do that until we change our attitudes to the fish we eat in Britain. We are out of date. It is as simple as that."

Next month, a conference, Sustainable Fisheries in 2050, is to be held in London. Scientists, fishing industry representatives, supermarket executives, consumer groups and conservationists will discuss ways to market Britain's new generation of fish stocks, to try to make them as popular as cod and haddock were in the past. "It is a tricky task but I am optimistic we can do that," said Simpson.

Problems lie ahead, however, an example being provided by the mackerel. Until recently, it was rated one of the sustainably caught fish in the North Sea with quotas having been agreed and established by the EU and Norway. Then the mackerel started to move north as seas warmed and stocks reached Iceland and the Faroe Isles. Their fleets started fishing the mackerel in vast numbers. The result was a major dispute with the EU and Norway: the so-called mackerel wars, which have yet to be resolved and which have seen UK ports blockaded so that Faroese and Icelandic fishing boats could not land there. "There will be lots more cases like this as the sea warms," said Roberts.

In addition, the impact of warming waters is hitting stocks and environments already battered by overfishing. For decades, trawlermen have dragged vast, 30-tonne nets with metal doors and chains over much of Britain's coastal waters, in an attempt to catch every cod and haddock they could find. Seabeds in places such as the Firth of Clyde have been ripped up and left utterly barren.

"Three-dimensional, complex habitats rich in coral, sponge and sea fan have been turned into endless monotonous expanses of shifting gravel, sand and mud," said Roberts. "Species that are now shifting their ranges north into these impoverished ecosystems will find very little to sustain them."