European eels take epic slippery route to breed before death

New research into mysterious migratory routes taken by eels to their ancestral spawning grounds has found those routes far more circuitous than previously thought.

Irish and fellow European scientists tracking European eels have found the nocturnal sea animals stagger their swim to the Sargasso Sea in the western Atlantic, where they breed before they die.

More than 700 eels, including a number caught in Ireland, were tagged and tracked over the 5,000km route to the Sargasso, near the Bahamas.

The 44 Irish eels were taken from the Corrib, Mask, Burrishoole, Shannon and Erne catchments, and released in Galway Bay, according to Inland Fisheries Ireland (IFI) scientist Dr Paddy Gargan.

The study found their swim takes longer than thought and that they may take in the Azores on their route.

One of the Irish eels tagged registered a swim of 6,982 km, and 273 days to take the trip - with the longest migration taking over 300 days.

Dr Gargan said the research also found the eels dive deep during daylight and come to the surface at night - a vertical difference of some 600 metres.

Ireland was one of four countries, along with Sweden, France and Germany, which released eels between 2006 and 2012 for the EU-funded study.

Slower-paced migration

The results overturn previously accepted theories about one large journey to the Sargasso, and also show the slower-paced migration makes them more vulnerable to predators.

Eel populations have been falling, and commercial fishing is no longer permitted, Dr Gargan points out. An EU recovery plan for eel stocks is in place.

Dr Gargan is one of the authors of a research article, Empirical Observations of the Spawning Migration of European Eels: The Long and Dangerous Road to the Sargasso Sea, published in science publication Science Advances..