When the opportunity arises, electric eels hunt in packs with wily tactics.
Electric eels are a genus of knifefish, not true eels.
This is the story of a group of Volta’s electric eel, living in a small lake on the banks of the Iriri River in the Amazon. Volta’s electric eel can reach lengths of 2.4 meters, and are capable of producing 860-volt electric shocks: the strongest electric discharge of any animal.
These eel live in the lake with lots of tiny tetras, which are only some 4 centimeters long. This prime opportunity requires savvy to take advantage of the situation.
For most of the day and night, the eels lay nearly motionless in the deeper end of the lake, only sporadically coming to the surface to breath. Electric eels get the most of their oxygen from air: an adaptation in response to the low-oxygen waters which they sometimes inhabit.
Electric eels are crepuscular: active during the twilight periods of sunrise and dusk. Electric eels are customarily solitary hunters, sneaking up on sleeping fish and jolting them into an easy-to-eat torpor.
On their own, the eels would have scant chance to dine on elusive tetras. The lake eels tilt the odds dramatically with their group coordination.
Once up for the hunt, the eels first interact with each other and go over the game plan. There over 100 that form a hunting pack. The eels then form a circle around thousands of tetras, herding the tiny fish toward shallow waters. Tightening the corral balls the tetras up.
With the tetras in the shallows, trapped by the main eel group, 2 to 10 eels break off, moving in closer and launching joint electric attacks on the prey ball.
The electric shocks send the tetras flying out of the water. The tetras splash down stunned and motionless. This lets the shocking eels and their compatriots easily pick off defenseless prey.
In a single twilight session the eels perform their group hunting ritual 5 to 7 times.
“Hunting in groups is pretty common among mammals, but it’s quite rare in fishes,” remarked Brazilian ichthyologist David de Santana. “Our initial hypothesis is that this is a relatively rare event that occurs only in places with lots of prey and enough shelter for large numbers of adult eels.”
When the occasion arises, dolphins use a selfsame technique as electric eels to corral their meals.
Douglas A. Bastos et al, “Social predation in electric eels,” Ecology and Evolution (14 January 2021).
“Scientists discover electric eels hunting in a group,” ScienceDaily (14 January 2021).