As part of the River Medina Restoration Project, a collaborative initiative delivered through the Isle of Wight Rivers Group and Newport Rivers Group, Environment Agency teams have installed a number of elver (juvenile eels) passes on a series of concrete weirs on the river.
Once common in British waters, the long-term future of the eel is bleak as the numbers entering European rivers has crashed by over 90 percent in recent decades. The decline is thought to be caused by a number of factors including over fishing, habitat loss, pollution, climate change and changes to oceanic currents.
Eels are unusual in that they start life in the ocean then grow in freshwater, before migrating back to the sea to spawn. One major concern regarding the survival of the European Eel is the presence of artificial barriers such as weirs, sluices and structures which prevent young eel migrating into our rivers to live out their adult life.
Figures indicate that approximately 20,000 hectares of stillwater habitat and 68,000 hectares of river habitat in Europe are inaccessible to eels due to manmade barriers, but the Environment Agency is dealing with this obstacle by installing eel friendly passes in waterways.
Data collected from fish population surveys carried out on the River Medina showed that very few eel were found in the upper catchment confirming the prediction that elvers were not able to swim up to the upper reaches of the river.
The elver passes are made using a four inch diameter flexible land drainage pipe with a “bottle brush” inserted through the entire length of the pipe. The pipe has a small amount of water passing through it which is gravity fed, and this provides a flow to help the elvers to find the entrance.
Dave Hunter of the Environment Agency’s Solent and South Downs Fisheries, Recreation and Biodiversity Team, said: “Due to the efforts of our specialist teams eel populations are being given a real chance to make a much needed comeback in rivers on the Island. This is great news, but more work needs to be done.
“These fish passes are relatively cheap and easy to install. Along with the habitat improvement works planned for the river, we hope that eel will be able to thrive in the Medina catchment which to date, they have been unable to do. This project is in addition to further extensive eel and elver migration projects across West Sussex, Hampshire and Isle of Wight area over many river catchments.”
Monitoring will be carried out in the spring of 2011 to assess the effectiveness of the new eel passes, and we hope to report back on this.
• Eels have a long-range lifecycle. They spawn in the ocean and their transparent larvae drift on ocean currents until they reach the continental shelf. As they approach the coast, they grow and take on a darker colour. Now called elvers, they enter estuaries and migrate upstream to grown and mature in rivers, lakes, ponds and wetlands as yellow eels. They can remain in freshwater for over 20 (and up to 40) years, before migrating downstream, taking on a silver appearance, to the sea. The mature adults are thought to migrate back to the mid-Atlantic to spawn. Truly one of nature’s great migrants.
• Eel are important to the diet of several other rare and protected species, such as otters and bittern.
• Eels are listed as endangered by the Convention on International Trade in Endangered Species.