Electric eels don’t seem to be the only ones I thought they were.
In a small lake deep in the Amazon River basin in Brazil, scientists first recorded fish not only living together, but actively working together to feed and kill their prey.
There is even evidence that the strategy works. From the abundant electric eels of the Volta (Electrophorus voltai, not a real eel, but a type of knife) found living in the lake, many were over 1.2 meters long and blooming.
“This is an extraordinary discovery,” said ichthyologist Carlos David de Santana of the Smithsonian’s National Museum of Natural History. “Nothing like this has ever been documented in electric eels.”
Not much is known about Volta’s electric eel. The fish was only recently discovered in a lake along the Iriri River and was officially described and recognized as a distinct species last year. But it has a fist, capable of discharging a single shock of over 860 volts – stronger than any other recorded electric eel.
De Santana and his team first spotted electric eel hunting in a group in 2012. More than 100 people appeared to be working together to herd and kill prey so that the entire bank could feed. But one observation was not enough to classify hunting as normal behavior.
In 2014, the team returned and found more Volta’s electric eels, so they started working on observing and recording the animals. After 72 hours of continuous observation, they saw the eels engaging in five more hunts. Not only was this enough to classify the behavior as normal, but it allowed the researchers to observe and record exactly how these “social looting events” occur.
Day and night, the electric eels rested for the most part. At dusk and dawn, during dusk, the electric eels were stirred to hunt. This, the team noted in their paper, is unusual: Volta’s electric eels are usually seen only feeding at night and solo.
The difference here is striking. On each occasion, more than 100 individual electric eels aggregated and began to swim in circles, effectively grazing smaller groups of fish, mostly caracini, in a “ball of prey” that they gradually escaped into shallower waters.
Then, once the ball of prey was squeezed out of nowhere, up to 10 electric eels moved forward and fired a powerful blow to the joint, stunning the prey – which would jump out of the water before falling back, meaningless.
“If you think about it, a person of this species can produce a discharge of up to 860 volts – so theoretically, if 10 of them are discharged at the same time, it could produce up to 8,600 volts of electricity,” he said. of Santana. “Approximately the same voltage required to power 100 bulbs.”
Once the prey was stunned, the joke could move and feed in its spare time.
The team found that each hunt lasted about an hour and involved five to seven electric shocks.
“Group hunting is quite common in mammals, but is actually quite rare in fish,” de Santana said. “There are only nine other species of fish known to do this, which makes this discovery truly special.”
However, although hunting may be normal, the team believes it could be quite rare. In their interviews with the locals, the congregation of electric eels and hunting behavior were not mentioned. So whether electric eels gather to hunt or go solo could depend on the right conditions, such as high abundance of prey, and specific locations with plenty of shelter for a large number of fish.
Although many are still unknown, the team believes the electric eels will return to the lake annually. They launched a citizen science project called Projeto Poraquê, where locals can record observations; these data could prove invaluable. And the team plans to return to the location in hopes of seeing the animals again.
“In addition to trying to locate additional populations of eels involved in group feeding, our future field and laboratory studies will investigate social predation in electric eels, focusing on the link between population, social structures, genomics and electrogenesis,” they wrote. They. in their newspaper.
“In short, this case provides a unique perspective for future studies on the evolutionary interaction between prey and escape tactics between vertebrates.”
The research was published in Ecology and evolution.