ABSTRACT
The life-history of freshwater eels is characterised by extensive marine migrations, initially as larvae and fi nally as maturing adults. However, many eels also undergo signifi cant migrations within freshwater when as juvenile fish, they gradually move upstream to find and colonise new habitats. This upstream migration of small pigmented eels (elvers) is best known for temperate species where it takes place during summer. At natural and man-made obstacles like waterfalls and dams respectively, large numbers of these juvenile eels often accumulate during their endeavours to surmount such obstacles and penetrate further upstream. These accumulations provide important monitoring sites for determining an index of juvenile eel recruitment; they also provide harvesting sites to seed upstream habitats or other catchments.
