Why are European eel endangered?

　　In addition to delicious, European eel has also plagued biologists for more than a century. They spend their adult life in estuaries and streams, and also, breed and travel to the Sargasso Sea near the Bermuda Islands. Subsequently, the tiny transparent juveniles returned to Europe on the Gulf Stream. However, the eel population has been mysteriously reduced, prompting people to take extreme measures to restore their numbers.

　　Now, researchers understand the dangers that young eel faces on the road: hungry fish. It has been thought that these eel infant are difficult to find and capture for most predators. However, a recent study exploring the traces of DNA in the gut of fish near the eel breeding water suggests that at least six marine species can quickly eat young eel.

　　European eel used to be very common, but its number has fallen sharply over the past 45 years. More importantly, the number of juveniles that eventually reached Europe by “glass eel” was reduced by 90%, causing some to wonder what they might have experienced. Are some creatures eating them up?

　　This seems unlikely. Young eel size, as well as a small willow leaf , was detected only once in the intestines of other fish at the end of the 19th century. It may also be that once swallowed, they disappear so quickly that they leave no trace. Mads Reinholdt Jensen, co-author of the paper and now a graduate student at Aarhus University in Denmark, said that in fact, this eel is hard to find, “even in a basin of water”. Researchers looking for a decline in the eel population analyzed all the possibilities, except who was eating young eel.

　　Jensen and colleagues at the University of Copenhagen did not analyze the young eel itself, but instead studied the DNA of 62 eel that the Danish team collected in 2014 and quickly frozen. The team wanted to find adult eel that spawned in the Sargasso Sea, but found nothing. The Jensen team developed specific molecular tags for eel. These labels can “catch” any eel DNA in the gut of fish. In the end, the researchers checked the DNA of European eel in six different fish species. They reported this finding in the journal Marine Biology, which was published a few days ago.

　　For the marine ecologist Tracey Sutton of Nova Southeastern University in Florida, USA, the latest findings were shocking. “This is contrary to the belief that these fish mainly feed on crustaceans. “The latest research shows a new approach to the food chain that we didn’t know before,” he explained. ”