By Helen Briggs BBC News
5 October 2016
Scientists are a step closer to solving the mystery of one of the great animal migrations.
Each autumn, eels leave European rivers to travel across the Atlantic Ocean to breed for a single time, then die.
Tagging studies show that the fish swim more than 3,000 miles (4,800 km) to the Sargasso Sea.
But, rather than one mass spawning in the spring - an idea held for a century - their arrival is staggered, UK researchers say.
"Eel migration is a rather romantic tale," said lead researcher David Righton, head of the Centre for Environment, Fisheries and Aquaculture Science (CEFAS) in Lowestoft.
"Eels only spawn once in their lifetime and then they die, so they're making this final journey of their life, towards the Sargasso Sea, to meet their life's goals, if you like.
"And so the fact that we've got a little bit of insight into that - but we've also got some new questions about how eels tackle that really fundamental problem of meeting that life goal - is really, really fascinating."
Mysterious life cycle
The life cycle of the eel has long puzzled scientists.
Even the Greek philosopher Aristotle pondered the question of where eels came from, deciding that they sprang up spontaneously from the mud.
Almost 100 years ago, it was discovered that their destination was the Sargasso Sea, in the western Atlantic near the Bahamas.
This led to the assumption that all eels took the shortest and quickest route across the ocean from freshwater rivers and streams.
"What we've found is that [some] eels actually take a more convoluted route to the Sargasso Sea," said Dr Righton.
"We propose that eels probably have a strategy that enables some eels to arrive in a very short period of time but others to take a longer, more meandering journey and perhaps arrive up to a year later and spawn in the subsequent seasons."
Eels arrive around the European coast as tiny glass eels, having drifted across the Atlantic for two or three years from the Sargasso Sea.