River dams blamed for driving once abundant eels to the brink of extinction

Hold the jelly; eels may be on the slippery slope to extinction, researchers say.

European populations of the fish are now just 1 per cent of what they were in the 1980s, and its American cousin is also reckoned to be in trouble: the numbers in the Great Lakes collapsed five years ago, almost ending the commercial fishing of eels. Denmark has also "wiped out" its eel population, and is struggling to reintroduce the species.

"There are almost no eels left in the Great Lakes," Willem Dekker, of the Netherlands Institute for Fisheries Research in Ijmuiden, told New Scientist magazine. Much of the problem is put down to damming of rivers. European and North American eels migrate from the fresh water where they normally live to an unknown spot in the Sargasso Sea, in the North Atlantic, to spawn and die.

In river estuaries, eel larvae become tiny, transparent "glass" eels. They change into yellow "elvers" as they head upriver, maturing as silvery adults decades later. But for many, damming of rivers has made that journey impossible. And nobody has managed to breed eels in captivity. Even so, glass eels are sold as a delicacy or sold to China and Japan.

"In Spain and Portugal, where the eel population is densest, dams have closed 90 per cent of the rivers to eels," Mr Dekker said. It was a similar story in other countries. Building "fish ladders" would help the eels past dams, Mr Dekker said, but few owners could be bothered.

Other pressures are also taking their toll, he added. The oily fish accumulates PCBs and other persistent chemical poisons, and many European eels are now infected with an Australian parasite imported from Japan. "We warned governments in 1997 that they had to control the fishery," Mr Dekker said. "They did absolutely nothing. If they act now, there may still be a chance. If not, we will lose the eel."

Latest estimates of eel stocks were presented last week at a meeting of the International Council for Exploration of the Seas in Tallinn, Estonia.