Bigeye Trevally

Photo: Mark Rosenstein · CC BY-NC

Bigeye trevally school in masses of several thousand individuals at Jokombo, forming the tight spherical bait balls that are a hallmark of current-swept seamounts with high prey productivity. The school's formation behaviour is driven by predation pressure — when a large tuna or shark approaches, the mass contracts instantaneously and individuals on the periphery swim faster to maintain their position inside the protective group. At night these schools disperse entirely, with individuals hunting independently across the reef, and dawn dives catch the reassembly process as fish aggregate back into the formation.