Migratory fish: the glass eel in Lake IJssel

Numbers of glass eels migrating to Europe and also to the IJsselmeer have been falling steadily since the early 1980s, with the result that eel catches have declined.

Trends

The eel grows up in fresh water and migrates to the sea as an adult, to breed. The young transparent "glass eels" or elvers appear off the Dutch coast in spring, to travel up the freshwater. It is not known exactly where the eels spawn: possibly near the Sargasso Sea in the Atlantic Ocean east of the United States.

After a period with high numbers of glass eels in the lake IJssel in the 1960s and 1970s, the arriving eels have declined steadily in number. A brief recovery from 1992 to1997 was followed by exceptionally low numbers again. This fall reflects the general decline in the migration of glass eels to Europe: numbers are now about 10% of what they were in the period before 1980. Throughout Europe, eel populations and eel catches have fallen sharply. The causes of the decline in the eel are not clear. Commercial eel fishery is most probably one of the factors. If fewer eel migrate to the sea to spawn, in subsequent years fewer elvers will appear off the coast. Other factors mentioned are pollution of the water, the loss of nursery grounds, and parasites introduced by humans. Nowadays, many of the eels sold for consumption come from eel farms. These farms are wholly dependent of catches of elvers, because eel does not breed in captivity.

The eel is on the Red List of freshwater fishes.