Every year, eels leave European rivers for a journey in a so-called "epic migration" to the North Atlantic's Sargasso Sea to breed for a single time, then eventually die.

However, a BBC News report said this final journey has long been suspected until, at present, there has been no direct evidence.

 

By fitting eels with satellites, scientists have tracked the creatures in their last leg of the route. They then said the information would help conserve the critically endangered species.

According to the Environment Agency's Ros Wright, who led the study, this is the first time they have been able to track eels to the Sargasso Sea, and they are delighted to have the first direct evidence of adult European eels to reach their spawning area.

Their journey, the study lead added, will reveal information about eel migration that has never been known in the past.

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European Eel

The European eel faces a lot of dangers throughout his life cycle. Such hazards include changes to ocean currents caused by climate change, poaching, pollution, and obstacles in waterways like dams and weirs.

The Environment Agency eel specialist Dan Hayter has been monitoring eels in the River Blackwater in Essex for two decades and has seen an extreme drop over that period.

Hayter described the eel monitoring work and said they "do catch eels every single day." Compared with the historic numbers, they are now quite low, and there has been a 95-percent drop since the 1980s.

Eel Conservation

Eels arise around the European coast, as small, fragile, and transparent glass eels, having floated across the Atlantic for two to three years from the Sargasso Sea.

They adjust to freshwater and mature in rivers, growing up to one meter long, until they are ready to swim back to reproduce once and then die.

To date, it has been quite challenging to investigate their migration throughout the ocean. Previous studies have followed adult eels to the Azores, although the trail went cold from there.

Through this study published in Scientific Reports, the researchers have now tagged adult eels in the Azores, showing "they can swim all the way all the way to the Sargasso Sea."

The Final Leg of the Journey

Describing their finding, Wright said they knew they could get as far as the Azores, although the final leg was just a country not discovered.

He added they thought if they could tag eels in the Azores, then they might fill the gap, and if they have managed this, they can confirm that they have filled in that final leg of the "journey to the Sargasso Sea."

Untangling the routes taken and identifying the location where eels are spawning is crucial for understanding the reasons behind their decline and informing conservation initiatives. 

As specified in the press release on the Gov.uk website, the eel's life cycle has long puzzled scientists. Even Aristotle, the Greek philosopher, pondered the question of where eels came from, deciding that they leaped up spontaneously from the mud.

Almost a century ago, it was believed that their destination was the Sargasso Sea, in the western Atlantic near the Bahamas, although until now, final evidence has been lacking.

Related information about eels' mysterious migration is shown on TED-Ed's YouTube video below:

 

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