LONDON -- The seas around Britain are starting to teem with fish species once deemed exotic as climate change raises water temperatures, forcing the former dominant occupants to flee northward toward the Arctic and opening the way for those from the hotter south, according to marine and fisheries scientists.

Such is the extent of the migration already observed, which is expected to grow in coming decades and could even force a change in the country's fish menus. Once-local species are moving farther afield and therefore becoming more expensive to catch, while formerly foreign ones become plentiful locally and therefore presumably cheaper and easier to harvest.

"People have started calling the North Sea the crucible of climate change. It has warmed by about a degree Celsius over the last 50 to 100 years, which is something like six times faster than pretty much any marine area around the world," John Pinnegar, program director of the Marine Climate Change Centre at the government's Centre for Environment, Fisheries and Aquaculture Science, told ClimateWire.

"We have seen quite a lot of warm-water fish becoming more abundant -- things like anchovy, red mullet, sea bass -- all of which are actually quite nice to eat," he said. "Species that we traditionally got in the Bay of Biscay area are now showing up in the Irish Sea and into the North Sea. At the same time, things like cod, a cold-water fish, seem to be suffering and moving northward.

"The British have very traditional fish eating habits -- historically consuming predominantly cod in the south and haddock in the north. Not many people are used to eating red mullet and sea bass. But eating habits can change, and that is partly what adapting to climate change could mean," he added.

Pinnegar said sea bass not only has quadrupled in quantity in the seas off southern England in the past 20 years, but is now being found by anglers as far north as Scotland and is being commercially fished off the coast of Yorkshire, 250 miles north of its former northernmost range.

The chips remain, but the fish are foreigners
Pinnegar was lead author of the marine and fisheries section of a vast U.K. government report earlier this year on all aspects of the risks associated with climate change. Among other findings, the report shows significant warming of waters around the United Kingdom in studies from 1961 to 1990 across all seasons but particularly marked in autumn and winter.

Although the picture is complicated by factors such as the impact of commercial fishing, water-based recreational activities and the growth of human coastal populations, scientists say the rising acidity of the seas due to absorption of carbon dioxide from the atmosphere and changing salinity and oxygenation is having an effect on fish and shellfish.

"Sea temperatures are rising -- although it is hard to say whether this is a blip in geological terms or evidence of global warming. But with it we would expect to see some changes in the species distribution of fish," said Richard Handy, director of the Ecotoxicology Research and Innovation Centre at Plymouth University's School of Biomedical and Biological Sciences.

"As the seas warm, we would expect to see some of the species of fish we more usually associate with the warmer waters off Spain to start appearing in the U.K. There have even been reports of fishermen catching barracuda and types of shark they haven't seen before," he added.

Fish food moves north, too
While some of the colder-water species will move north to escape the heat, the rising water temperatures could also have an impact on those that remain as their metabolisms speed up with the warmth and they need to eat more. Meanwhile, the plankton and other species lower down the food chain have already moved on and so become scarcer.

The Marine Climate Change Impacts Partnership -- a group combining scientists, government departments, nongovernmental organizations and the fishing industry -- in its annual report card for 2012 said the dominant cold-water zooplankton species in the North Sea had declined 70 percent since the 1960s, while many plankton species had moved 10 degrees of latitude north in the same period. That equates to a distance of nearly 700 miles.

At the same time, deepwater species like monkfish had moved steadily deeper to keep cold, while shallow-water species like sole had moved steadily higher with the warmth.

The MCCIP report card also noted that some fish species had already moved north 30 to 250 miles over the past 30 years and said that by 2050 they could have added a further 135 to 375 miles.

Sole, seemingly perversely, has moved south against the trend. In previous winters it always migrated north from the Dutch coast's shallow waters, which became unbearably cold in winter while the deeper North Sea remained relatively warm. Now it stays put as the water remains warm throughout the year.

The warming waters also appear to be a boon for squid, and in Scotland many trawlers are switching to hunting that.

The changing movements and ranges of commercially exploited fish stocks have also produced some unexpected conflicts, with trawlers having to follow the fleeing fish farther afield and into the territories of other nations. This has already happened with mackerel moving from off Norway to off Iceland, while Spanish trawlers are starting to venture into U.K. waters in search of anchovy.

Some winners, some losers
"The model predictions suggest that Iceland and Greenland -- Greenland in particular -- and Norway are probably going to benefit in terms of fisheries from climate change, at least for the next 50 to 100 years," Pinnegar said.

"Things like the cod populations are projected to really boom further north, and it is already starting to happen," he added. "The herring populations are projected to do quite well, too. Those are really big commercial stocks.

"From the modeling that has been done, it looks like the U.K. is almost at the break-even point. We gain some species and we lose some species. But in terms of our fisheries, it will probably balance out almost," he said.

But with the good comes the bad. Invasive species such as the zebra mussel have been extending their ranges northward, and some marine-borne bacteria usually associated with warmer water are also expected to move in.

The marine impact section of the U.K. government's Climate Change Risk Assessment particularly notes the possibility of Vibrio cholerae, associated with outbreaks of cholera in humans from eating contaminated shellfish, arriving in force off U.K. shores as the temperature climbs. There have already been outbreaks in Spain, and scientists in the United Kingdom are on watch.

It also warns of the potential arrival of other water-borne Vibrios such as V. parahaemolyticus, which is associated with seafood bacterial gastroenteritis in humans. This is already very common in the United States, with more than 10,000 cases in a year, against about 40 in the United Kingdom.

"Assessments based upon global sites suggest that changing climatic conditions could result in increased rates of infection and illness in humans via shellfish and through bathing," it says.

Reprinted from Climatewire with permission from Environment & Energy Publishing, LLC., 202-628-6500