Eel

(European Eel)

(Anguilla anguilla)

Order: Anguilliformes Family: Anguillidae

Foto: Ari Saura

Description: In Finnish fresh-waters eel is the only fish with a single continuous dorsal fin, which has grown together with the anal fin and vestigial caudal fin. The only remaining paired fins are the pectorals. The head is relatively small and pointed. The skin is thick and covered with small scales and a thick protective coating of slime.

Origin and distribution: Though occurring in many waters in Europe and North Africa, the eel has declined alarmingly in all its habitats. In Finland, eel runs used to be abundant in the rivers Kymijoki and Kokemäenjoki. The eel has even been known to migrate as far north as the Artic Circle. The damming of rivers for hydroelectric power has almost completely prevented the natural spawning runs of the eel, but it currently occurs as a stocked species in several watersheds.

Reproduction: Eels are believed to begin their life in the deeps of the Sargasso Sea in the Atlantic Ocean. They are assumed to spawn in a water layer at a temperature of about 17−20 ^oC and at depths of about 150−400 m. However, not a single mature or well developed eel or fertilized egg has ever been caught. The smallest larvae found in the Atlantic have been 5−7 mm long. Leptocephalus larvae rise to surface waters after hatching, and disperse taking advantage of oceanic currents and streams. Two or three years later they reach the coasts of Europe in June, where they metamorphose into transparent glass eels and migrate upstream to estuaries on the Atlantic coasts of Western Europe. The eels that move upstream to the rivers of the Baltic Sea are somewhat older, yellow eels.

Diet, growth and migrations: Eels feed on benthic organisms and also on small fishes, mainly at night in the summer months. In lakes, the growth period continues for 6−9 years for males and 8−15 years for females. At its largest, an eel can be over 1 m long, weigh 3−4 kg and have attained an age of 20 years. When approaching maturity, eels begin their 6000-km-long spawning migration back to the Sargasso Sea. Migrating eels have never been caught in the ocean, and their method of navigation is still poorly understood.

Fishing and catches: Measured as price per kg, the eel is one of Finland’s most valuable fish. Owing to the low numbers, however, it is of only minor significance overall. Eel stocking started over 100 years ago, though not in any great quantities until the 1960s−1970s, when more than 8 million glass eels were introduced. Importing of glass eels was prohibited from 1979 to 1989 because of the risk of fish diseases. The annual eel catch was 70−80 tonnes in 1978−1980 but, with the end of stocking, had fallen to less than 30 tonnes by 1985. Stocking was restarted in 1989, and since then the annual catch has picked up. Eels are usually caught by long line, hook and line, fish trap or trap net.

Vulnerability, threats and management: The amount of glass eels migrating upstream to European rivers has fallen drastically, being only one per cent of figure in the early 1980s. Proposed reasons for this decline are over-fishing, environmental toxins, the parasite nematodes of the Japanese eel, natural population dynamics, and also the northward shift of the northern edge of the Gulf Stream. Up to 95 per cent of all eel catches in Europe comprise glass eels, the majority of them being used for cultivation and the remainder for stocking in the wild. Nowadays almost all eels in Finnish inland waters originate from stocking. The Evaluation of Threatened Species in Finland 2000 does not include the eel among nationally threatened species, as it does not reproduce in Finland; in Sweden, however, it is regarded as critically endangered (CR).

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