Cod has had its chips as sole invades North Sea
September 20 2011 Lewis Smith
Changes in the water temperature have put an end to hopes that the North Sea cod population can return to the levels it enjoyed in the 1970s.
Warmer conditions have altered the availability of prey species and driven the cold-loving cod northwards so even if the fishery is managed perfectly the species will only make a limited recovery, a senior scientist at the Centre for Environment, Fisheries and Aquaculture Science (Cefas) has warned.
But as species such as cod are moving northwards their place is being taken by fish including Dover sole which, having previously tended to prefer the Bay of Biscay and Mediterranean, are finding the warmer conditions – the North Sea has warmed by 1.3C in 30 years - to their liking.
Dr Stuart Rogers, divisional director for environment and ecosystems at Cefas, will outline the changes in a keynote speech at the ‘Appetite for Change’ conference on September 23 that launches the Aldeburgh Food and Drink festival.
Speaking before the conference he said: "The cod stock is still under a great deal of pressure. There are signs of recovery but there have been environmental changes over the last five decades which suggest we won’t be getting back to stock sizes that we had in the 1970s.
"The 70s were unique. Things have moved on in the environment. Over the last 20 years the temperature of the North Sea has risen significantly. There has been a change in the distribution of cod and many of the species that it relies on for food. Even if we reduced our exploitation pressure the population wouldn’t have the environmental conditions it needs to return to 1970s levels."
Sole, however, are approaching the point that stocks are at maximum sustainable yield: "It’s partly linked to technical measures like gear design and making sure vessels that are old can leave the industry without being replaced. It’s a good example of a success story in the southern North Sea in that it has responded to management. The environmental conditions are supporting good management."
Anchovy, John dory, sea bass and red mullet are other species that have shifted into British waters in increasing numbers in recent years. "Species that 10 years ago would have been considered vagrants are becoming almost established," he said. "Anchovies are much more common now in the north sea and there is a red mullet fishery."
Dr Rogers will also tell the conference that competition between industries operating in Britain’s waters is as great as ever, with fishing interests challenged by emerging wind technology and the oil and gas sector.
They will, he said, have to co-operate and Dr Rogers sees signs that the wind industry is trying to be conciliatory to the fishing interests.
Safety concerns mean trawlers generally have to keep away from areas of the sea where there are wind farms in case they get driven into the turbines or snag underwater cables. But smaller 10 m boats could operate there and wind farm developers have started to drop rocks to the seabed to encourage lobsters to thrive near turbines. Other future initiatives that might boost the fishing industry is the use near wind farms of floats from which mussels can be grown on ropes.
His comments on fish populations changing because of warming waters were backed up earlier this month by the release of research demonstrating that 72 per cent of common fish species in Europe’s waters have experienced rises or falls in population due to temperature rises.
Hake, dab, red mullet and John dory were named among the benficiaries, with cod and haddock among the losers. The study, led by Dr Steve Simpson, of the University of Bristol, looked at records accumulated over 28 years in 11 different surveys covering more than 100 million fish.
Dr Simpson said: "Temperature has a strong influence on egg maturation rates, growth and survival of fish larvae, and impacts on the planktonic communities that underpin the food webs that sustain commercial fisheries.
"We see many more southerly warm-water species faring well on the European shelf than northerly cold-adapted species. This means more small-bodied, faster growing species with shorter generation times, and potentially more diversity."
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