^{Prue Wheeler via Storyful}

Prue Wheeler was out for a morning snorkel along Western Australia’s Ningaloo Reef on May 5 when she saw an extraordinary sight: schools of fish forming a bait ball that then slowly diminished in size.

A bait ball is created when small fish move tightly packed in a spherical formation around a common center. It is a defensive measure adopted by small schooling fish when they are threatened by predators.

Wheeler said in her post;
"As I jumped in for our morning snorkel yesterday at a regular snorkel & dive site off Coral Bay. I was treated with this nature show...
These small pelagic fish were being preyed upon by large predatory fish (mainly grey reef sharks & barracuda - also targeted by the seabirds from above). In awe I watched this baitball slowly diminish in size with this evolved, sophisticated evasion techniques displayed by the bait fish as they react to a predator with lightening reflexes, these defense maneuvers almost appear choreographed as their silver bodies dazzle in the most incredible formations. Unfortunately for these bait fish this is the last defensive measure adopted by fish schools when they are overwhelmed & the more effective defense strategies have broken down."