Eels meet again

One of the most mysterious fish of the western Atlantic is the European eel. Its range is vast: adults spend the bulk of their life in freshwater systems from Iceland to Morocco. And, indeed, the species has supported one of the biggest fisheries in Europe, employing up to 25,000 people at its height. But, as with many other commercial species, stocks are now in dangerous decline. The number of young eels returning from the sea to river systems has declined to one per cent of the numbers recorded in the 1970s. Action is urgently needed if the species is to survive but its geographic range and complex life history hampers conservation efforts. Adults are thought to breed in the Sargasso Sea, near Bermuda, although breeding has never been directly observed. But the smallest seen larvae have been found in this area and these are thought then to drift on the Gulf Stream and North Atlantic Current back to Europe and north Africa. Here they change and enter freshwater environments, where they live for many years before changing again and heading back out to sea on their final journey to breed. Recent evidence has also suggested further complications, in that the population appears to be genetically fragmented, so that returning adults may perhaps only breed with others from the same river systems from which they left, adding to the problems facing the species. But new work by Johan Dannewitz at the Institute of Freshwater Research in Drottningholm, Sweden and colleagues in Sweden and Belgium (reported in the Proceedings of the Royal Society series B, published online), describes a genetic analysis of eels sampled at more than 40 sites across Europe and, more importantly, those examined from some sites over eight years between 1994 and 2002. The results represent 'the most extensive genetic study, with respect to the number of locations and individuals analysed, of the European eel to date,' the authors say. On the basis of the statistical analysis of their results, genetic differences over time at particular sites outweigh geographical differences, suggesting that the eels might comprise a single breeding population. The authors believe their results suggest that a single population-wide conservation strategy is therefore more desirable, rather than national efforts, if the species is to be effectively conserved.