Mackerel Bait ball
The process that leads to the formation of a bait ball typically starts when predators locate a fish school deep below the surface. The predators make rushes and use various scare tactics to force the fish school to the surface, herding it at the same time into a compact volume. The alarmed fish, trapped against the surface above and surrounded all about, abandon their coordinated schooling movements and become chaotic. Their graceful and disciplined schooling strategies of uniform spacing and polarity degrade into frenetic attempts by each fish to save itself.
In this way, a dense bait ball forms as each fish scrambles to get away from the surface of the ball and hide in the interior. The symmetry of this centripetal action forms a sphere, the shape with the minimum surface area for a given volume. This exposes the fewest number of fish on the surface to the predators.
The movement, sound and smell can attract more predators, including different predator species, until there is a carousel of them, each species using their own characteristic predatory strategies. Fish that break loose are singled out and eaten. A frenzy can develop as predators compete, the water reddening with blood as shredded flesh and scales drift to the depths. As the bait ball reduces in size and number, it becomes progressively easier for the predators to target the remaining survivors.
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