European eel
Anguilla anguilla
John Spilsbury sent these two photos of an eel he caught in the River Tame at Reddish Vale, ok they are not up to his usual excellent standards, but he was wrestling with a very slippery customer and only had his mobile phone to capture the moment.
The European eel has a interesting life cycle.
They are international marine travellers only completing part of their life cycle in freshwater and coastal areas.
Spawning has never been observed, but is thought to take place in the spring, deep in the Sargasso Sea between Bermuda and the Bahamas.
Although eggs have never been collected, maturing females are reported to contain up to 10 million eggs. The eggs develop into a leaf like larva. It was thought that these larvae took up to three years to migrate from the Sargasso Sea to the European coast, but recent studies suggest that the journey may take as little as12 months.
Eel larvae, photo, from Wikipedia
When the larvae reach European waters they change into what is called the glass eel stage before continuing with their migration. In the British Isles, from around
May, once the temperature has reachedabout 10 degrees celsius, the glass eels make their migration from estuaries to freshwater.
Once the glass eels develop pimentation they are known as elvers, and are very similar in shape to adult eels. In freshwater the eel lives on or near the bottom, often digging into gravel, and migrate slowly upstream. During this period they are known as yellow eels.
Male eels stay in freshwater for between 7 and 12 yrs, maturing at an average length of about 36cm. Females stay between 9 to 20 yrs and mature at a larger average size of 50cm, though
Glass eels, photo from Wikipedia
the eel can grow up to 1 meter in length and live up to 40 yrs. When eels mature, they change to a blue/silvery colour, and are known as silver eels, they then migrate seaward during the autumn, usually on dark stormy nights.
Populations of eels have become increasingly threatened as the number returning to European rivers has declined dramatically over recent decades. In one study, it was estimated that numbers had fallen by 90% since the early 1980s, and recent studies suggest the number of new glass eels entering British rivers has now dropped to 1% of former levels. Eel populations are now considered to be “outside safe biological limits”
The crash happened over the whole European continent with no single, obvious cause. Suggestions for possible causes have included over-exploitation, inland habitat loss, climate and ocean current change, disease and pollution.
Some more eel facts.
Eels secrete a slimy substance all over their bodies, which is thought to protect them from changes in salinity.
Eels are capable of surviving for periods of time out of water and can cross land and damp meadows in their search for water systems.
Eels prefer to move when it is dark and large migrations are known to occur on wet, stormy nights especially when the half moon is on the wane. This knowledge is exploited by commercial fishermen fishing for glass eels.
Mature eel, photo from Wikipedia
