This month we are highlighting one of my favourite species that can be found in the river, the European eel. This is a species that undertakes an incredible journey and can live for a very, very long time. Believe it or not but the oldest recorded eel was over 80years old! Remarkably there are also reports of one eel that was believed to be over 150 years old! This was a fish known as the Brantevik Eel and lived in a well in Sweden, before it died in 2014. Whilst there is some controversy around this number, we do know that they can easily reach ages of over 50 years old in the right conditions.
Closer to home, the Mersey and Gowy catchments appear to be a very important location for eels with good numbers still recorded. Sadly, this is not the case for many UK rivers, with one of the biggest problems for eels being the installation of weirs and hydroelectric schemes that prevent upstream migration. Poor water quality and overfishing have also contributed to a reduction of eels in our rivers. In fact, because of the decline in eel numbers, they are now classed as critically endangered On the IUCN Red List, with a 90% decline in elvers (the juvenile stage of eels) being recorded in UK Rivers.
For the fish that do make it into the Mersey, there are a number of different routes that take them to the hearts of major cities like Liverpool and Manchester via the canal systems, or to quiet remote farm ponds and upland rivers in the Peak District and Cheshire plains. Regardless of where they end up though, at some point, sometimes decades after they entered the river, they will once again feel the pull of the moon and head back out to sea. Read on to find out more about the incredible journey eels undertake.
When eels first arrive in the Mersey, they are almost completely transparent and are affectionately known as glass eels (like in the photograph above left), even at this stage they can already be up to 3 years old! Having spent the very early stages of life drifting as larvae in the ocean currents. Once in the river, they take on the darker colouration of the more commonly seen elver (like in the picture above right).
The juvenile fish will then find a home either in the river itself, or amazingly, they will travel over land and find themselves in ponds, lakes, canals and reservoirs. Here they feed on worms, snails, shrimps and even fish and slowly they grow bigger and bigger before eventually reaching adulthood. Once mature, the eels will make their way back into the river systems before once again returning to the sea and their long journey back to the breeding grounds in the Sargasso Sea. The Sargasso Sea is a mysterious place located within the Bermuda triangle of the East coast of North America. Very little is known about eel breeding behaviour but slowly through satellite tagging studies some of the mysteries are beginning to be solved.
Due to the complex migratory behaviour it is currently impossible to breed European eels in captivity making them very vulnerable to exploitation and making conservation of the species very difficult. For the Mersey eel this means that to successfully spawn, they will have to complete a journey of over 13,000km, that’s the equivalent of driving the full length of the UK over 13 times!
We have been working really hard with a team of researchers at Manchester Metropolitan University to try and develop a new method of surveying for eels. With the help of local angler and eel enthusiast Peter Baker (pictured right) we were able to collect a small mucous sample that we have been able to extract eel DNA from. This little fish will help us to unlock some of the secrets about eel movements within the rivers and canals around the UK. This is a really exciting project and we hope that our brilliant student, Molly, will be able to provide an update on this project in one of the future newsletters. Also, we’d like to say a huge thank you to Peter for his help and the tireless work he does for eel conservation.
For us in the Mersey, eels are, (for the time being at least) still quite a common sight with both fishermen and birds regularly catching them. Eels are enjoyed by cormorants, grey herons, bittern and even some of the gull species, as well as being a favourite food for another Mersey resident, otters. We hope you agree that they are an incredible species with a fascinating lifecycle and are one of the real long-distance wanderers of the seas.
Keep an eye on our social media pages for updates on this and our other projects. We might also have some exciting volunteer opportunities for anyone wanted to get involved with eel conservation.
Lastly we’d also love to hear from you. Please get in touch with any eel photographs or stories you’d like to share with us!
Andrew Wolfenden, Biodiversity Manager