When you think of great transformations in wildlife, your mind will probably conjure up images of butterflies emerging from their chrysalis, or a tadpole losing its tale, growing limbs and becoming a frog. What if I told you there’s another creature that can be found in our local rivers which transforms five times over the course of its life? A life which can last for over two decades and span continents! You’d be eel-ated, wouldn’t you?

The European eel. They might not seem like much to look at, but they have a fascinating lifecycle which starts near the island of Bermuda, in the Sargasso Sea. It’s here that they hatch from eggs as transparent, leaf-shaped larvae (also known as leptocephalus) and join the Gulf Stream as it sweeps across the Atlantic Ocean.

They drift for 4,000 miles, over a year or two, before they reach the shores of Europe and North Africa. This is where their first transformation takes place, as they become finger-length, see-through eels known as glass eels, and continue their journey inland.

The Severn Estuary is a welcome sight for these young, adventurous eels, as they migrate upstream in search of a freshwater and estuarine habitat. Along the way, they grow and their skin darkens, and they’re now known as elvers.

Elvers have been found in the nearby River Trym. Peter Coleman-Smith, from the Trout in the Trym community group, explained: “We have a small number of freshwater eels in the Trym of varying sizes from a few centimetres (elvers) up to about 45cm. There are also reports of eels in the Henleaze Swimming Lake, which is close to the Trym. 

“I am sure there were once many more eels using the Trym to grow as it's the first tributary of the River Avon which fish migrating up from the sea will reach. 

“Conversations I've had with a few folks in the Sea Mills area indicate there were far more a few decades ago. So, we have them, but they are rare!”

To help them with their onward journey, the Somerset Eel Recovery Project made and installed eels ropes in Westbury Wildlife Park. These help the young eels to navigate the weir and keep heading upstream.

Once they’ve found themselves a freshwater habitat to settle down in, their bellies become yellow and they now known as yellow eels. They can remain in this state for more than 20 years! 

Bristol Water and Bristol Avon Rivers Trust previously ran the ‘Spawn to be Wild’ project, where local schools looked after a tank of elver and released them into Blagdon lake after six week. Around 4,000 eels have been released through this project, which taught local school children all about eels and how to protect them. There’s also an eel trap at Blagdon Reservoir, which allows Bristol Water to transfer eels into Blagdon Lake, where they can remain until they’re ready to reproduce.

Once eels are ready to spawn, they make their final transformation and change colour again, into silver eels. Then it’s time for the almighty journey back to where it all began, the Sargasso Sea. Amazingly, no one has observed eels mating in the wild, so there’s still one mystery left that these magicians have to reveal!

Euopean eels are critically endangered, having rapidly decline over the last 40 years. A 15 year study of European eels in the Bristol Channel published in 2012 found that since the 1980s, on average eel populations have declined by 15% each year. This left the population of eels at the time of the study’s publication at only 1% of 1980s numbers.

This dramatic loss is caused by a variety of factors, including overfishing and illegal fishing (glass eels are a delicacy in some places), habitat loss, pollution, invasive parasites, climate change and blockage of migration routes. It’s this last factor that we can do something about.

If you’ve been inspired to take action for eels, check out The Somerset Eel Recovery Project, Bristol Avon Rivers Trust and Trout in the Trym to find out more about river cleans, wildlife monitoring and eel rope building sessions happen near you.