eels

eels belong to the Anguilliformes, an order of fishes with nineteen families that typically have snakelike bodies and a serpentine mode of moving. Most marine eels live on the seabed, but there are some extraordinary midwater species like gulper eels (e.g. Eurypharynx spp.). Cutthroat eels (Synathobranchus spp.) are attracted in large numbers to baited cameras deployed on the bottom at abyssal depths (>4,000 m/13,000 ft). Conger eels (Conger conger) are large predatory inhabitants of rocky areas that are frequently caught by anglers. The many species of moray eel (family Muraenidae) inhabit coral reefs where they hunt fish and Crustacea like crabs. The best-known eels are the Anguilla species (of which there are seventeen species). The European eel (Anguilla anguilla) lives most of its life in fresh water, but breeds in deep water somewhere in the Sargasso Sea, no one is quite sure where. It evolved about 60 million years ago when the Atlantic was still quite narrow, but ever since has been steadily opening up 1–2 millimetres a year. So the larvae, which once had a journey of a few hundred kilometres to get to European rivers, now have to travel 4,800 kilometres (3,000 mls.).

A newly hatched eel larva is known as a leptocephalus. It has an elongated flat leaflike body that is highly transparent. It is a weak swimmer, and takes about three years to drift across the Atlantic in the flow of the Gulf Stream. Somehow the larvae find their way into estuaries, where they metamorphose into elvers. When they first enter the estuaries the elvers are still transparent and are known as glass eels, but soon become black. On high spring tides elvers migrate, en masse, upstream keeping close to the banks. They even cross land during wet weather. They live in streams and rivers for about three years growing to over a metre in length. Then they migrate back to the sea, again metamorphosing to become silvery with enlarged eyes. It is not known how they find their way back to the Sargasso Sea to spawn, but it is likely they ride the return flow of the current gyre. The numbers of elvers returning to European rivers are reported to be diminishing, which may reflect subtle changes in the currents of the North Atlantic.

Bibliography

Fort, T. , The Book of Eels (2002).

M. V. Angel