Squid and anchovies, more commonly eaten by Britons holidaying abroad, are being drawn into UK waters in large numbers by climate change, according to major new report that suggests the nation’s long-lost bluefin tuna is also returning.

However, global warming is harming sea birds, such as puffins, fulmars, terns and razorbills, as the fish they rely on are driven north or deeper as waters warm. The analysis of the impact of climate on the UK’s seas, which draws on the work of 400 scientists, found a steady rise in water temperature.

It also found a clear rising trend in sea level, leading to much more frequent extreme high water events. Improved defences and forecasting have prevented an increase in coastal floods, but the report warns that sea level rise around the UK is likely to accelerate.

Squid were seen in the North Sea only occasionally in the past but have increased “dramatically”, according to the report, with thousands of tonnes now caught each year and mostly exported.

“The difference now is it is an established summer trawl fishery – that is a clear change,” said Matthew Frost, chair of the working group that produced the report for the UK Marine Climate Change Impacts Partnership (MCCIP). He said fishing boats had been quick to spot the new stocks: “If something comes, they realise that very quickly.”

Anchovies have followed the same path northwards. “You now have an anchovy fishery, which is clearly linked to climate change – that is what the science is showing,” said Frost.

The anchovies come from the Bay of Biscay, where there is a large Spanish and French fishery and the shift could have political ramifications, he said, especially after Brexit when the UK takes back control of its territorial waters. “The shift leads to political implications around who is allowed to catch what and what the quotas are, so it is an important development.”

Bluefin tuna were common around the UK before the second world war, with the giant fish a popular target for “big game” fishermen. The decimation in later decades of the mackerel and herring that tuna eat then saw the giant fish disappear.

But shifting mackerel and herring populations and warming waters have seen the tuna return. “Sightings are definitely becoming more frequent,” said Frost, with large shoals seen off south-west England in 2015 and 2016.

The report is an update on the MCCIP’s first analysis in 2006. At that time, it found that sea bass was becoming more common as temperatures rose. But it has not become established as an important catch, due to overfishing, said Frost: “It is a very popular fish to eat.”

However, as fish suited to warmer water move north into UK waters, cold water fish seeking cooler temperatures are moving out, including cod. A dramatic reduction in fishing has seen North Sea cod recover to sustainable levels from near collapse in 2006, but their recovery would probably have been even greater without the warming of the sea.

The UK’s waters are heating by about 0.5C per decade. “That may not sound like a lot to us but it is really significant in terms of the biology and ecology,” said Frost. Part of the reason is that rising temperatures give a higher baseline, making hot spells even more extreme.

Many British sea birds are struggling to cope with climate change with populations of Atlantic puffins, fulmars, black-legged kittiwakes and common, Arctic and little terns all finding the fish they eat harder to come by. Severe summer storms are also having an impact, particularly on razorbills, whose nests can be damaged and whose chicks die more often.

The report also predicts that over the coming century some species, such as the great skua, Arctic skua and Leach’s storm petrel could become extremely rare or even extinct in the UK.

Sir David Attenborough praised the scope of the new report: “Concern about the state of our seas has caused them to be studied more intensively – and extensively – than ever before. They have never been more important.”

Other physical changes considered by the report include the frequency of extreme water levels. It found the tide was above 5.75 metre at a reference site at Newlyn in Cornwall for almost 60 hours in 2015. In contrast, that level was never reached for more than 30 hours a year between 1915 and 1985.

The strength of the Gulf Stream, the flow of warm water up the Atlantic which is a key factor in the UK’s mild climate, is weakening, the report found. But a collapse of the current, which would plunge the UK into a much colder climate regime, is unlikely this century.

The scientists also reported increasing acidification of the ocean, as carbon dioxide rises in the atmosphere and is absorbed by the seawater. This may harm the ability of animals to form their shells but the higher CO2 could benefit some algae and seagrasses.

Overall, the impact of climate change on the UK’s seas is a mix, Frost said: “Some things will be of benefit – a good example is new fisheries, and it could even increase biodiversity in some cases. But of course the knockback to that is the increased frequency of very intense storms and potential for flooding.”