French scientists have raised the alarm about a rapid shrinkage in the size of sardines in the Mediterranean and Atlantic, caused by the warming climate.

Sardines in the Mediterranean have lost two thirds of their average mass over the past decade while those in the Atlantic waters off France have lost half their weight, according to Ifremer, the French oceanographic institute.

Since the institute was alerted by Mediterranean fishermen in 2008, the fish there have shrunk in length from an average of 13cm to 10cm last year, it said. In the Bay of Biscay, their size dropped from an average of 18cm to 14cm last year.

Experts at Ifremer ruled out overfishing, disease or the impact of predators and concluded that a rise in water