Surveillance scheme reveals travel arrangements of mysterious eels

Eel catcher Peter Carter going out on the Well Creake to trap eels on a misty dawn out on the fens.

Eel catcher Peter Carter going out on the Well Creake to trap eels on a misty dawn out on the fens. - Credit: Matthew Usher

They are the mysterious species which gave their name to the historic city of Ely, and until recently were caught in the Great River Ouse.

Now scientists have discovered the secrets behind the travel arrangements of eels after a surveillance scheme which has tracked their 2,000km journey from lagoons in the Mediterranean to the Atlantic ocean.

Scientists, including from fisheries research centre Cefas, claim to have ended a long running debate about whether eels in the Mediterranean were trapped there and unable to find the Straits of Gibraltar and navigate back to the Atlantic.

The European eel is an endangered species; the population of European eel has become seriously depleted over the last three decades.

Earlier this year Peter Carter - Britain's last remaining traditional eel fishermen - decided to hang up his traps, ending a practice that has passed, largely unchanged, through countless generations.

The Outwell based Fenman said he had decided to give up, after struggling with changes to fishing laws and a fall in eel stocks.

But scientists said their tracking work proving their escape to the Atlantic shows that Mediterranean eels are likely to be able to reach the spawning area in the Sargasso Sea and contribute to future generations of eels.

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During their migration, eels moved to deep water (up to 800m) during each day and into shallower water (~350m) at night-time. A report from Cefas said that this was the same type of behaviour as reported in other studies of eel migration, although they are not clear why eels do this, speculating it might be to regulate temperature, to avoid predators, or for navigation.

'When eels reached the Straits of Gibraltar, they abandoned their vertical migration and instead swam to the seabed. There, they took advantage of outward flowing currents to make their migration to the Atlantic easier. After exiting the Straits they resumed their daily vertical migrations.

'Better understanding of eel biology will help us to manage their populations across Europe and beyond more effectively. Eels are an important food fish in Europe, often cooked in regional speciality dishes, such as the famous eel and mash shops in London,' the report said.

Dr David Righton, the principal Cefas Scientist said: 'These new data on the oceanic migrations of European eels show what an amazing species this fish is. Eels are mysterious creatures and hard to study, especially in the deep ocean. Our results are a triumph of technology, logistics and high quality eels.

'Many scientists have questioned whether eels could escape the Mediterranean because finding the Straits of Gibraltar is like finding a needle in a haystack. All of the eels migrated west after release, and two of them made it more than 2,000km from release and into the Atlantic.

'This is a great achievement for the team, and a significant scientific finding.'

The team attached satellite trackers to eight eels captured in lagoons of Salses-Leucate and Gruissan, southern France.

The effort was led by Elsa Amilhat and a team from the University of Perpignan, with the help of the local fishermen, and in collaboration with researchers from Cefas (UK), DTU-Aqua (Denmark), and the University of Agricultural Sciences (Sweden).

The research was funded by the French Ministry of Ecology. Several months after release, the trackers resurfaced and communicated their final position via satellite, in addition to depth and temperature data collected during the migration. The data was then used to map the migration paths in detail.

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