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Watching eels cross the ocean

European Eel (Anguilla anguilla).
[Image courtesy of Eva Thorstad]

It is extremely difficult to track the movements of individual fish in the ocean but it seems that scientists are getting closer to that goal. This week in the journal Science, a team of researchers report that they have successfully followed a group of European eels during the first 800 miles of a long, 3,100 mile migration.

The eels were making their yearly trek from the coast of Ireland to the Sargasso Sea, near Bermuda in order to mate. Kim Aarestrup and colleagues attached miniaturized satellite transmitters to some of the eels, and used them to map the first part of this tremendous journey.

European Eel (Anguilla anguilla).
[Image courtesy of Bernt Rene Grimm]

Their data provides new information about the swimming direction, depth, and migratory behavior of these European eels and it also shows that the eels encounter a wide range of different environments along the way.

Aarestrup and the team of researchers found that the eels stayed in warm surface water at night, but at dawn, they dived down between 650 and 3,280 feet into cooler waters and stayed there during the day. The researchers suggest that the warm water at night could help the eels to keep their metabolism and swimming activity up.

They also suggest that cold water during the day might delay the development of the eels' reproductive organs until they reach the warm, tropical waters of the Sargasso Sea, where they will finally mate.

In the future, this type of satellite tracking technology might be improved so that researchers could track the entire journey of these eels to mate.