Eel Anguilla anguilla; Linnaeus, 1758. Family: Anguillidae
Description
The European eel ( Anguilla anguilla) in fresh water is unmistakable. It has a highly distinctive, elongate, snake-like brown body with yellow flanks. Minute scales are deeply embedded in the skin. The animal has a protruding lower jaw with small blunt teeth. The dorsal, caudal and anal fins form a continuous fringe; pelvic fins are absent.
The eel is widespread in Europe, being found from Iceland and North Cape in the north, to the coasts of Morocco in the south, and the Black Sea in the east. Eels can be found in all types of water body, including both upland and lowland, flowing water and still, and productive and unproductive waters, although they probably prefer rich, muddy, slow-flowing environments.
Life History and Behaviour
Eels are the only European fish to leave the European coast to spawn in the sea. Depending upon growing conditions (i.e. temperature and food availability) male eels spend anywhere between seven and 20 years, and females between nine and 50 years, in fresh water before returning to the sea and maturing. Body condition may be the stimulus to migrate. The eels become silver in colour and migration is greatest on dark, moonless nights.
The gonads mature when the eels enter the sea. They utilise their high fat reserves (up to a third of their body weight) on migration to their spawning grounds in the Sargasso Sea. Spawning takes place in the spring. Although no spawning adults have ever been found, newly hatched leptocephali larvae, 5 mm long, have been recovered at depths of 100-300 metres. The larvae feed on plankton and grow to 25 mm in two months. Travelling eastwards on ocean currents, they metamorphose into un-pigmented 'glass eels' as they reach the Continental Shelf, eventually arriving on the Atlantic coast of Europe in something like 12 months. As they near the coast, pigmentation begins to develop and they spend some weeks in estuarine waters preparing to enter freshwaters as 'elvers'.
It has recently been discovered that a substantial proportion of eels never enter fresh water at all, but instead remain around the coasts of Europe, whilst others make frequent migrations back and forth between fresh, brackish and salt water throughout their lives. Eels grow faster in coastal and estuarine environments than in freshwater, and perhaps the fresh water stage in Europe should be regarded as an adjunct to the migration from tropical to temperate seas, rather than the sole purpose of the journey.
The eel has a varied diet in fresh waters, feeding habits varying with size and location. Smaller animals tend to feed on vertebrates; larger animals take an increasingly large proportion of fish. Little food is taken in winter.
Eels and People
World-wide, eel species are in decline, both in terms of juvenile stocks and adult catches. In Europe glass eels were formerly used for direct consumption or for stocking rivers, but the number of juveniles arriving from the Atlantic has steadily fallen since 1980 and is now at perhaps just 5% of its average level in the 1970s. At the same time the demand for glass eels has increased, because they serve as 'seed' for the growing world market in eel aquaculture. A fishery for glass eels exists in the north west of Scotland and the Hebrides. The scale of this fishery is unknown, and indeed eel fisheries in Scotland have never been regulated.
Since the eel grows very slowly in the cool, nutrient-poor waters of Scotland, populations are highly vulnerable to over-exploitation. Consequently there is little tradition of fishing for adult eels in Scotland. With the exception of a few long-established traps on rivers (now largely, or perhaps entirely, abandoned), most commercial fishing has been by itinerant fisherman from England or continental Europe. Elsewhere in Europe, adult eels form probably the single most economically important freshwater fishery.
In 1998, however, ICES declared that "the European eel stock is outside safe biological limits and the current fishery is not sustainable." Protective measures are being implemented in Europe: in September 2007 the European Union issued Council Regulation (EC) No 1100/2007 establishing measures for the recovery of the stock of the European eel, requiring member states to produce Eel Management Plans that setting measures to reduce anthropogenic mortalities of eels sufficiently to ensure that escapement of silver eel biomass is at least 40% of the escapement that would have been expected if no anthropogenic influences had impacted the stock. In practise this will involve the reduction or closure of many European eel fisheries. In addition, the eel is due to be listed on Appendix II of CITES from March 2009, so that all trade of eels from the EU to the rest of the world will require a statement of non-detriment from a competent scientific authority.