A bait ball, or baitball, occurs when small fish swarm in a tightly packed spherical formation about a common centre.

[5][6] Some species of forage fish, driven by nutrient availability and their life-cycle stage, form vast schools at predictable locations and times of the year.

Schooling fish are easier to attack once they abandon their free streaming behaviour and form into a tight bait ball.

Many predator species have learned that by interacting cooperatively they can panic schooling fish into forming a 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.

Their graceful and disciplined schooling strategies of uniform spacing and polarity degrade into frenetic attempts by each fish to save itself.

[10] Swordfish charge at high speeds through forage fish schools, slashing with their swords to kill or stun prey.

[14][15] Gannets plummet from heights of 30 metres (100 feet), plunging through the water and leaving vapour-like trails behind like fighter planes.

The attraction of huge numbers of prey fish means that these predator species, which might otherwise be mutually antagonistic, usually cooperate with each other in pursuit of their common goal.

[30][31] In 2001, Clua and Grosvalet proposed a four stage model to describe mixed species feeding behaviour involving common dolphins, tuna and shearwater sea birds.

The run, containing millions of individual sardines, occurs when a current of cold water heads north from the Agulhas Bank up to Mozambique where it then leaves the coastline and goes further east into the Indian Ocean.

A similar great migration of herrings occurs each year during the summer plankton bloom along the coast of British Columbia and Alaska.

In winter, the coastal fjords and inlets are relatively lifeless, and the resident Steller sea lions must dive deeper and further from the coast to catch the widely-dispersed herring.

Spring storms disturb nutrients in the water which, together with the strengthening power of the sun, act as the catalysts for the plankton bloom.

The finale to the programme features unique underwater footage of humpbacks engulfing whole bait balls, and reveals their co-operative hunting behaviour called bubble-netting.