Carousel feeding

[1] The term carousel feeding was first used to describe a similar hunting behaviour in bottlenose dolphins (Turslops truncatus) in the Black Sea.

During the feeding phase several orcas begin to eat while the others continue herding the fish to maintain the ball.

It has been speculated that surface feeding is beneficial because the animals do not have to deep dive so energy is saved, and since the pressure is less intense each tail strike is more effective.

The final stages of herding include blowing bubbles to tighten the ball, flashing the orca's white underbelly to blind and disorient the herring, and slapping the sea surface with their tails.

[7] In addition, the fish are debilitated by the pressure change and turbulence which makes it easy for the orcas to catch them.

A carousel feeding event can last from ten minutes to three hours depending on the herring available and the number of orcas in the pod, as well as environmental conditions.

[9] Some of the strategies orcas employ include producing large waves to knock seals off ice floes, or even beaching themselves to catch sea lions.

[10] The strategies orcas develop depend on their typical prey type and the most efficient method to capture them considering environmental conditions.

Norwegian orcas have developed carousel feeding because it is an effective method to capture spring-spawning herring.

Cod and saithe are also common in the area but studies examining the stomach contents of Norwegian killer whales show the primary biomass consumed is from herring.

In the summer many Norwegian orca pods move to the coast of the Lofoten and Vesterålen islands where adolescent herring, mackerel and saithe are more abundant.

Since herring are the Norwegian orca's main food source it is clearly adaptive to have produced a cooperative feeding method specific to the predation of this species.

This means the orcas do not completely deplete their food source and potentially the strongest herring will survive the event.