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 orcas are attracted to an abundance of squid to feast on, funneled there by a special configuration of narrow canyons.

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 20 kilometres across and around 1 kilometre down. Initially, researchers were puzzled that the orcas found that …