Orcas feast off the coast of Australia Jochen Kaempf

At the same time every year around 150 orcas meet 50 kilometres off the south coast of Australia, and now we may know why.

The extraordinary congregation happens between January and April and the orcas spend their time feeding and playing in a surprisingly deep patch of water around 40 kilometres across and around 1 kilometre down. Initially, researchers were puzzled that the orcas found that particular region so appealing as the surrounding ocean is low in nutrients.

Jochen Kaempf at Flinders University, Australia, suspected the geometry of the ocean floor …