European Eel

European eels undergo five stages of development in their lifecycle: larva (leptocephalus), glass eel, elver, yellow eel, and silver eel. Adults in the yellow phase are typically around 45–65 centimetres (18–26 in) and rarely reach more than 1.0 metre (3 ft 3 in), but they can reach a length of up to 1.33 metres (4 ft 4 in) in exceptional cases. They have 110 to 120 vertebrae. They tend to live approximately 15–20 years in the wild, although some captive specimens have lived for over 80 years. One such specimen known as "the Brantevik Eel" lived for 155 years in the well of a family home in Brantevik, a fishing village in southern Sweden.

Eels tend to range 0–700 metres (0–2,297 ft) underwater. After spawning in the Sargasso Sea, they disperse northwards throughout the Atlantic Ocean, its coasts, and the rivers that empty into it. Feeding occurs mainly at night via scent, with prey consisting of worms, fish (including ones too big to eat without biting off chunks), mollusks such as slugs, crustaceans such as crayfish, and occasionally plankton, when available in large quantities. European eels are preyed upon by larger eels, herons, cormorants, and pike. Seagulls also prey on elvers. Eels usually find and compete for shelter by hiding in plants or in tube-shaped crevices in rocks. They also hide in muddy fields when inland.

As the European eel population has been declining for some time, several projects have been initiated. In 1997, Innovatie Netwerk in the Netherlands began a project in which they attempted to get European eels to breed in captivity by using a swimming machine to simulate the 6,500 km (4,000 mi) journey from Europe to the Sargasso Sea.

The European eel is a critically endangered species. Numbers of eels reaching Europe is thought to have declined by around 90% (possibly even 98%) since the 1970s. Contributing factors include overfishing, parasites such as Anguillicola crassus, barriers to migration such as hydroelectric dams, and natural changes in the North Atlantic oscillation, Gulf Stream, and North Atlantic drift. Recent work suggests that polychlorinated biphenyl (PCB) pollution may be a factor in the decline. The TRAFFIC program is introducing traceability and legality systems throughout trade change to control and reverse the decline of the species. The species is listed in Appendix II of the CITES Convention. Hydroelectric dams have been shown to have a significant negative impact on eel populations.