The brown eel is an endangered species but the ESB (Electricity Supply Board) has killed 300,000 of them at its hydro-electric dam on the River Erne at Ballyshannon.

The tiny juvenile eels, known as elvers, survived a perilous journey from where they hatched from eggs in the Sargasso Sea 4,000 miles away across the Atlantic Ocean only to be suffocated to death in an ESB trap.

Dr. William O’Connor from the European Eel Consultancy in Limerick described the incident as a failure of international significance and estimated that more than 336,000 elvers had died.

He said it was a “major and unnecessary kill of a critically endangered species”.

Ironically the traps in which the eels perished are there to ensure the small, worm-like fish get into the Erne. They can’t climb over the ESB’s huge hydro-electric dams at Cathleen’s Falls, at Ballyshannon, and Cliff, near Belleek. So the eels are trapped and transported by road around the dams.

An ESB spokesman confirmed that there had been an “regrettable incident” at Cathleen’s Falls over the Easter weekend.

“It would appear that an exceptional number of elvers entered one trap overnight at the very start of the season, exceeding the trap tank storage capacity with consequent mortalities in the order of 112 kgs,” he explained.

He said the ESB is working with DCAL (Department of Culture, Arts and Leisure) in Northern Ireland and IFI (Inland Fisheries Ireland) in the Republic in carrying out a full investigation into the incident.

The spokesman said trapping protocols are being updated as a result.

“This investigation is ongoing and a final report will be published in the coming days,” he added.

“In conjunction with IFI and DCAL, ESB has successfully operated an elver trapping programme at the station for over five decades and remain committed to this important conservation programme,” he stated.

“Despite this regrettable incident, ESB can also confirm that as of May 7, 461 kgs of live, healthy elvers have been trapped at the station and successfully moved North in conjunction with DCAL. This represents a significant increase on previous elver runs and so the trapping operations carried out by ESB and DCAL will continue as required,” the spokeman said.

Hydro-electricity is regarded as environmentally friendly because it does not produce the carbon dioxide associated with climate change. However, it has proved to be anything but environmentally friendly for the fish in Lough Erne, particularly eels and salmon which must migrate between the Erne and the Atlantic Ocean to complete their life cycle.

The eel begins life on the other side of the world, emerging from eggs laid among the tangled forests of seaweed in the strange surroundings of the Sargasso Sea, close to the notorious Bermuda Triangle. Millions of these tiny fish migrate across the Atlantic Ocean, arriving off the coast of Ireland between November and March as translucent glass eels not much bigger than a darning needle. Many migrate into our lakes and rivers between May and September as elvers and older bootlace eels. There they will live for up to 40 years, feeding voraciously during the summer before swimming down to the bottom and burying themselves in the mud at the onset of the first frosts to wait out the winter in a state of hibernation. Eventually they will get the urge to reproduce, turning silver and heading back to the Sargasso Sea where they will spawn and complete their life cycle.

Eels were fished for commercially on the Erne for generations but with numbers plummeting across Europe a total ban on their commercial exploitation came into force four years ago.

Scientists who have been studying eels have reported an increase in the numbers of juvenile eels returning to European waters in recent years.

Dr. O’Connor said: “Everybody is surprised that over the past three years the numbers of juvenile eels, called glass eels or elvers, arriving into European rivers has increased markedly.

“This year we’re in the middle of a particular record run of juvenile eels - perhaps the best run that has happened in the past 30 years,” he added.

However, he believes the system of trapping and transporting eels around hydro-electric dams is not working as it should.

Referring to the deaths of the eels at Ballyshannon, he said: “I know mistakes have been made and people have been caught off guard in terms of both elver trapping and the assisted migration programmes and also the monitoring of elver numbers, and we have quite clearly seen that this has not been done properly.

“But the current upturn is a tremendous opportunity to manage eel stocks sustainably going forward and we’d like to see the positive message of this upturn,” he added.

“The European eel was a species that was all but written off up to two years ago and the species has certainly surprised everybody in eels with this fantastic turnaround in fortunes,” stated Dr. O’Connor.