Deprived of pelvic fins, the eel takes on the air of snake. This fish has the astonishing characteristic of living in fresh waters and reaching the sea to reproduce. Let us follow the eel on its long journey.
Presentation of the eel
Eel is the vernacular name for several fish longiformes lacking pelvic fins, including the deep-sea eel, the deep-sea eel electric, the American eel, the spring eel or the spiny eel. In France, the most common species is the eel ofEurope also called common eel (Anguilla Anguilla). The animal grows in fresh water and migrates to the sea for reproduction (it is then said amphibiotic or diadrom). Its silhouette recalls that of the snake, hence its name (from the Latin anguish, the snake).
Description of the eel
The serpent-like body of the eel has small scales and abundant mucus that makes it viscous and difficult to grasp. Its long dorsal and ventral fins merge at the tail and are inserted behind the pectoral fins (characteristic of the family of Anguillidae). The fish has a brown-green back and a belly yellowish in young subjects (yellow eel). Her back is tinted with black and her belly with reflections silvery in individuals ready to perform migration (silver eel). The lower jaw is slightly longer than the upper and the nostrils are tubular. The European eel measures 40 cm to 150 cm and weighs up to 6 kg for females which grow larger than the males.
Distribution of eels at sea
The range of the European eel extends from Iceland and Lapland, to North, as far as Morocco and the Canary Islands, South. As seen above, the eel must imperatively reach the open sea to spawn. During this breeding phase, the distribution of the fish extends over all the coasts of theAtlantic North: from Florida to Greenland, from Senegal to Scandinavia, as well as in the Mediterranean and the Black Sea.
Environment of the eel
Eel is a said fish euryhalin : its ability to adapt to changes in temperature and salinity water allows it to colonize all continental aquatic environments: lagoons, coastal marshes, estuaries and sources of rivers when these lead to the Atlantic Ocean or the Mediterranean. However, the animal prefers the waters stagnant (brackish or soft), shallow, where it buries itself in loose sandy-muddy bottoms. It is also found at more than 1000 meters of altitude, in rivers at salmon and trout, where the current is lively and cooler temperatures.
Migration and reproduction of the eel
To reproduce, the European eel goes thousands of kilometers into the sea of Sargassum where she ends her life. The journey to reach this sea located in the center-west of the Atlantic Ocean is estimated from six months to more thana year. This low current area – near the origin of the Gulf Stream and the Bermuda Triangle – characterized by waters with high temperature and salinity essential for breeding. Eels lay eggs at a depth of 500 meters above a depth of 6,000 to 7,000m.
Phases of eel development
During its life, the European eel knows 5 steps main processing:
- After hatching, eels begin their life as larvae flat and transparent called leptocephali. For about a year, they drift from the North Atlantic to the European coasts;
- As they approach estuaries, eel larvae metamorphose into elvers. Their bodies are refined starting with the head and tail. Elvers will begin to migrate into fresh water to feed while growing;
- Going up streams and rivers, elvers turn into young eels also called eels ;
- In contact with fresh water, their bodies take on color in a few weeks: the back becomes olive brown and the belly yellow, hence their name of eels. yellow. They are generally considered to be sedentary on average ten years;
- When migration reproduction, the eel again undergoes transformations to adapt to marine life. Her skin thickens, her back darkens, and silver highlights appear on her sides and stomach. We speak at this stage of eel silvery.
Omnivorous with tendency carnivorous, the eel adapts its diet according to the environment in which it lives. This hunter nocturnal is guided by a very developed sense of smell which allows it to easily locate its prey. In seawater, the eel mainly eats small crabs, marine worms and crustaceans, but also fish (gobies, sticklebacks, etc.) and gastropods such as periwinkles or bivalves (mussels, cockles …). In fresh water, it is fond of larvae and nymphs ofinsects (dragonflies, mosquitoes, bloodworms …) small fish (roach, bleak) and earthworms. During his growth, the eel can swallow up to 25% of its weight daily in order to build up reserves of fat because she fasts as soon as the temperature drops below 10 ° or when it exceeds 30 °.
At the stadium larval, the animal is subject to significant predation by other fish. Having arrived in inland waters, glass eels are in turn consumed by many predatory fish, such as pike, zander but also by large eels. As adults, they are the food of larger predators such as otters and birds. piscivorous (cormorant, heron). Namely that eels at the glass eel stage are also very coveted by fishermen.
In addition to overfishing and poaching, threats to the eel are parasites, construction of dams that disrupt their migrations and pollution by pesticides in particular of water courses which influences its fertility and weakens its immune defenses. Classified as Critically Endangeredextinction, the eel now benefits from a management in all the countries of the European Union aimed at reducing the causes of its mortality. These measures include in particular a fight against poaching ; strengthening of fishing supervision (professional and leisure); the fight against pollution; the restoration of its habitats, restocking streams from caught glass eels. The European eel has a lifespan of 50 years.
Photo credit: BMR & MAM