Several important fish species that for centuries have been part of the staple diet of people in the Mediterranean region are abandoning sub-tropical seas because the water is too warm and are heading north.
Sardines, which for generations have been the most abundant commercial fish species in Portugal, are moving away. They are now established in the North Sea, and are being caught in the Baltic—a sea that until recently was normally frozen over in the winter.
Sardines, anchovies and mackerel—three fish species that are important in the diet of many southern European and North African countries—have been studied by scientists trying to discover how climate change and warming seas are affecting their distribution.
As well as the affect on the fishing industry, the abundance or disappearance of these species is crucial for many other marine species that rely on them for food.
A pioneering study, published in Global Change Biology, analysed 57,000 fish censuses conducted over 40 years, and has tracked the movement of these fish during this period.
It confirms that the continued increase in water temperature has altered the structure and functioning of marine ecosystems across the world. But it also shows that the effect has been greater in the North Atlantic, with increases of up to 1.3 ºC in the average temperature over the last 30 years.