(CN) — In the heart of the Brazilian wilds, researchers have discovered a lake that is home to scores of electric eels shrewdly working together to bring down elusive prey, despite once being regarded as a species that exclusively hunts and dines alone.
Deep in the untamed lands of the Amazon rainforest off the banks of the Iriri River in Brazil, C. David de Santana and a team of scientists have discovered a small, unassuming lake fed by the waters of the nearby river. The lake, no deeper than 10 feet at its lowest point and well populated by a network of sunken logs, quickly captured the attention of researchers for a single, perplexing reason: living among the underwater debris are over 100 electric eels, all living in remarkably close quarters considering their history of being – like most fish – largely solitary predators.
While this discovery alone was fascinating enough to warrant recognition, researchers observed the eels had also devised a complex hunting ritual that relied on dozens of eels working together in tandem to catch their prey – a never-before-seen behavior for the electrified creatures.
In a study published Thursday in the journal Ecology and Evolution, senior author de Santana of the Smithsonian's National Museum of Natural History and his colleagues detailed these unprecedented observations that could fundamentally change the way we look at electric eels.
At the heart of this new discovery lies Volta's electric eel. This unique variant of eel, just recently discovered in 2019 by de Santana, is capable of producing shocks with a record 860 volts of electricity and can grow up to nearly 8 feet long under the right conditions.
Researchers found that the 100 eels residing in the small river basis were these rare Volta's electric eels, and their observations only grew more intriguing from there.
The eels largely kept to themselves during the bulk of the day and night hours, content to rest in the deeper portions of the lake and only come up to the surface for the occasional gulp of air. But in the dusky hours of twilight, the eels began to stir, according to the study.
After swimming with and interacting with one another for a brief period, the cabal of eels began to swim in the formation of a giant ring, and at the heart of their formation were newly trapped schools of tetra, small 1-to-2-inch fish that are natural prey to eels but can often be too fast and small for an eel to catch alone.
Once the tetras were encircled by the electrified circle, the eels would herd the fish to the shallowest parts of the lake, areas that are barely 3 feet deep.
It was here researchers say they observed a tactic more in line with the that of a pack of wolves or hungry killer whales than a gang of eels. After herding the tetras to the shallow waters, small groups of up to 10 eels separated from the formation to form smaller, more concentrated hunting parties. These small groups then charged at the pack of tetras and delivered a series of coordinated electric attacks, packing such a punch it often sends the tetras flying out of the water before splashing motionless back down.
De Santana noted that considering the already awesome electrical power of just one of these eels, such well-orchestrated assaults were likely producing energy at an astounding level.
"If you think about it, an individual of this species can produce a discharge of up to 860 volts – so in theory if 10 of them discharged at the same time, they could be producing up to 8,600 volts of electricity," de Santana said in a statement. "That's around the same voltage needed to power 100 light bulbs."
Once all the tetras were shocked into submission after around half a dozen high-voltage bombardments, the eels moved in and made quick work of the defenseless fish. All told, researchers say the entire process took just around an hour.
While there is still much to learn about this new hunting strategy, researchers believe that the eels likely only congregate and hunt in this manner on a yearly basis, a rare event that only takes place whenever eels stumble across an environment rich in prey and outfitted with proper shelter.
To help identify more of these astonishing attacks, researchers have launched the citizen scientist program known as Projeto Poraquê that can allow users to log and report sightings of other similar hunting congregations.
Regardless of what further information comes to light, de Santana said Thursday’s study makes clear that there is still much more experts don’t understand about the lifestyles and hunting habits of electric eels, and that researchers need to aggressively expand their knowledge base for these creatures as we navigate an environmental future gravely threated by climate change.
"Electric eels aren't in immediate danger, but their habitats and ecosystems are under immense pressure,” de Santana said. “This paper is an example of how much we still don't know, how many organisms whose life histories we don't yet understand."
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