Social predation in electric eels

Abstract

Social predation-when groups of predators coordinate actions to find and capture prey-is a common tactic among mammals but comparatively rare in fishes. We report the unexpected social predation by electric eels, an otherwise solitary predator in the Amazon rainforest. Observations made in different years and recorded on video show electric eels herding, encircling shoals of small nektonic fishes, and launching joint predatory high-voltage strikes on the prey ball. These findings challenge the hypothesis that electric eels may have a single foraging strategy and extend our knowledge on social predation to an organism that employs high-voltage discharge for hunting. Thereby offering a novel perspective for studies on the evolutionary interplay between predatory and escape tactics.

Keywords: amazon fishes; feeding strategy; fish behavior; xingu river.

FIGURE 1

Schematic illustration of stages involved in the social predation as observed in 2014. (a) Identified behavioral states throughout 24 hr. (b) Aerial perspective during each stage. Stage 1, resting: electric eels were seen laying almost motionless, close to the mud bottom or among submerged fallen branches and trees; Stage 2, interacting: showed increased activity by swimming near the water surface and interacting with each other in the resting area; Stage 3, Migration: group of eels move from the resting area to the hunting area; Stage 4, hunting: groups of over 100 eels aggregate and start swimming in circles, herding groups of small fishes into a “prey ball,” and posteriorly launching a joint predatory strike. (c) Transversal section of the resting (Stages 1 and 2) and hunting (Stage 4) areas; showing the different patterns of spatial occupation by electric eels in the study area and in the water column