Blackfin Barracuda

Photo: Mark Rosenstein · CC BY-NC

Blackfin barracuda form dense cylindrical schools of hundreds to thousands of individuals in the open water above the blue hole arch, rotating slowly in a defensive formation that reduces each individual's predation risk. The school uses the current channelled around the reef point as an energy-efficient holding position, and the fish feed at dawn and dusk when the formation breaks up and small fish are pursued individually. The sheer mass of the school creates a living curtain that can temporarily block sunlight entering the blue hole, creating dramatic shadow and light play in the water column.