A tightly packed, spherical mass formed by small schooling fish, such as sardines or anchovies, as a defensive response to being hunted from multiple directions by predators including dolphins, sharks, seabirds and larger fish. By clustering together, individual fish reduce their own chance of being singled out, and the resulting feeding frenzy, especially during South Africa's seasonal sardine run, is among the most spectacular predator-prey events in the ocean.
Facts
PeriodicityMost years off southern Africa between May and July (sardine run) 1 ScaleShort-lived, seldom lasting longer than 10 minutes 1 Identification
Distinguishing AppearanceA densely packed sphere of fish, the shape exposing the fewest fish to predators 1 Connections
Associated With
A bait ball is a defensive formation that small schooling fish or krill form specifically under active attack by predators, and does not occur in the absence of a predation event.
Bait balls are a hallmark, extensively documented feature of the sardine run, forming as predators drive dense shoals of migrating sardines into tight defensive spheres near the surface.
Sources
1. Bait ball - Wikipedia
Duration
The bait balls are short-lived and seldom last longer than 10 minutes.
Sardine run timing
Most years, off southern Africa between May and July, billions of sardines
Appearance and formation
The symmetry of this centripetal action forms a sphere, the shape with the minimum surface area for a given volume, thereby exposing the fewest fish on the surface to the predators.
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