Whales Preying on Eels in Deep Atlantic Ocean

When the threatened European eels cross the Atlantic Ocean to get to the Sargasso Sea to spawn, they swim in deep water. But this does not protect them from predators, researchers from the University of Southern Denmark report: Even in deep water the eels are hunted and eaten according to a new paper entitled “Evidence of marine mammal predation of the European eel (Anguilla anguilla L.) on its marine migration” published in the Deep Sea Research Part I: Oceanographic Research Papers.

Fisheries biologists studying the European eel have found that the creature is hunted by whales even when it is swimming in the deep ocean where it typically is considered safe from attack.

Fisheries biologists studying the European eel have found that the creature is hunted by whales even when it is swimming in the deep ocean where it typically is considered safe from attack.

University of Southern Denmark biologist Magnus Wahlberg said it’s surprising that whales are hunting eels because there is not much historical evidence supporting the finding. Prior to Wahlberg’s study, there was only one instance of an eel being found in a whale’s stomach, according to the University of Southern Denmark, which explains why the marine mammals have usually not been included in discussions of the European eel’s natural enemies. The European eel is in decline, and all over the world biologists are struggling to map its mysterious life cycle in order to bring its numbers back up. One of the great puzzles is why and how the eel each year travels thousands of kilometers to get to the Sargasso Sea to spawn.

A European monitoring project has provided a group of eels with data loggers before their big trip across the Atlantic, and now biologist and associate professor Magnus Wahlberg from Southern University and colleagues from DTU have got a surprising message from the data loggers:

“It turns out that eels are hunted and eaten by whales. It happens in surprisingly deep waters where we normally think that the eels would be safe”, he says.

It might be quite common for whales to hunt eel in deep water and that we just have never seen it before

To date only a single case of a whale with an eel in its stomach has been described in the scientific literature. So these large marine mammals are usually not included in the discussion, when biologists talk about the eel’s natural enemies. “We do not know exactly which whale species are at play, but a good guess would be the pilot whale”, says Magnus Wahlberg.

According to the recorded depth profiles it is unlikely that the hunters were seals. “Seals do not dive this deep. The dive patterns better suit that of a pilot whale“, according to Magnus Wahlberg. However he is not quite sure what the new data on eel hunting in deep water mean. “It might be quite common for whales to hunt eel in deep water and that we just have never seen it before. This knowledge may be important for understanding how marine deep-water ecosystems functions“, says Magnus Wahlberg.

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