Wednesday, 23 October 2013

Spawn to be wild - eels in the rivers and streams of the south west

Many species that we know and love here in the South West can claim to have interesting and complicated life cycles, but none are quite as mysterious as that of the European eel (Anguilla Anguilla). They are in fact a type of catadromous fish – that is, they migrate from fresh water into the sea to spawn. For centuries the eel’s life history was not understood, even amongst the many fishermen who regularly caught both the larvae and the more mature stages without realising that they were related. Then in the early 1900s a Danish researcher concluded that the Sargasso Sea, in the western Atlantic near the Bahamas, was the most likely spawning ground and that the larvae slowly drift towards Europe on the Gulf Stream. We now know that after a journey of a year or more, the larvae metamorphose into transparent "glass eels", enter estuaries and start migrating upstream. After entering fresh water, the glass eels metamorphose into elvers, miniature versions of the adult eels. And this is where the trouble begins. Sluices, weirs, flood defences – these all seriously hamper the eel’s migration upstream to a suitable site where they can mature and grow, sometimes to as much as a metre in length in a mature female - before they begin their migration back to the Sargasso Sea to spawn.

Sadly the European eel is now endangered, but the good news is that Bristol Water and the Environment Agency have come up with a solution to help the eels’ migration upstream. Eel passes, that look a bit like a large upside down brush, allow the elvers to navigate up through weirs to a specially designed trap, the first of which has been operational at Bristol Water’s Blagdon pumping station for a few months now. This captures the elvers every night so that they can be safely released into the lake the next morning. Children from Ubley Primary School joined us to launch a fantastic new project which will help raise awareness of this strangely charismatic creature. We are also delighted to announce that four schools in the Congresbury Yeo river area will have the opportunity to rear young elvers in a tank in their classroom for several weeks whilst learning about the local water courses and how they can help to protect them for wildlife, before making the trip to Chew Valley or Blagdon lakes to release them. Who knows, in 20 years’ time their children might be watching the offspring of these elvers as they arrive here after their very long journey all the way across the Atlantic Ocean!
Cathy Mayne

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