Eel Anguilla anguilla; Linnaeus, 1758. Family: Anguillidae
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 North Africa 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 are generally thought to 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 three and 30 years, and females between five and 50 years, in fresh water before returning to the sea and maturing. Body condition may be the stimulus to migrate and the eels become silver in colour. Migration is greatest on dark, moonless nights in autumn.
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 after about two years. 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 quite 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 freshwater 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 individuals tend to feed on vertebrates, whilst bigger ones 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 widely 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 per cent of its average level in the 1970s. At the same time the demand for glass eels increased, because they serve as 'seed' for the growing world market in eel aquaculture, indeed a small-scale fishery for glass eels formerly existed in the north west of Scotland and the Hebrides.
Little is known about historical fisheries for eels in Scotland, because until 2009 the fishery was unregulated. Since the eel grows very slowly in the cool, nutrient-poor waters of Scotland, populations are highly vulnerable to over-exploitation. Consequently there was little tradition of fishing for adult eels in Scotland. With the exception of a few long-established traps on rivers (the last known of these closed in 2005), most commercial fishing in the 20th century was by itinerant fishermen from England or continental Europe. Elsewhere in Europe, adult eels have formed 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 have been 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. These plans were required to set in place 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 affected the stock. This has led to the reduction or closure of many European eel fisheries, including in Scotland, where fishing for eels, by any method, is prohibited without a licence from Scottish Ministers under a freshwater fish conservation regulation introduced in 2009. The eel was listed on Appendix II of CITES from March 2009, so that all trade of eels from the EU to the rest of the world requires a statement of non-detriment from a competent scientific authority. In 2011, the species was listed as Critically Endangered on the International Union for the Conservation of Nature (IUCN) Red List.