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.
The researchers report that the revelation has implications for European eel conservation efforts because this hunting occurs while the eels are swimming across the Atlantic Ocean to spawn in the Sargasso Sea.
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.
"It happens in surprisingly deep waters where we normally think that the eels would be safe,"Wahlberg said. "We do not know exactly which whale species are at play, but a good guess would be the pilot whale."
Wahlberg and his team reached their conclusion after fitting 156 European eels with data logging devices before releasing them in to the ocean for their westward journey across the Atlantic.
Three of the eels never made it to the Sargasso Sea to spawn, their data loggers were found washed ashore, where passersby found them and returned them to the scientists.
The data loggers continued to operate after the eels had been consumed, recording depth and temperature, revealing a puzzling increase in temperature in the cold Atlantic waters at a depth of 600 meters. The water temperature rose from 10 degrees Celsius to 32 C, which the researchers believe is indicating to the eel being eaten by a large, deep-diving mammal.
"Seals do not dive this deep. The dive patterns better suit that of a pilot whale," Wahlberg said. "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."
Wahlberg and his colleagues published their research in the journal Deep Sea Research Part I: Oceanographic Research Papers
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