How Blue Planet II filmed the fish that uses 'tools' to break open clams

Sequence director Rachel Butler explains how the filming team spent 100 hours underwater on Australia's Great Barrier Reef to capture the fish that uses 'tools'.

We called him Percy because he’s so tenacious. Persistent Percy.

About five times a day he would swim to find a clam and then return to this one bit of coral that he would use as a kind of anvil – smashing the shell until it broke. Sometimes it would take him five minutes – other times it would take an hour. We’d be swimming around and you could hear the smashing – properly hear him knocking against the coral.

I think we have all been quite staggered by the physical and cognitive abilities of a lot of the animals that live in our blue planet. I don’t think any of us were quite prepared for what we would find down there.

In any habitat it’s nice to have animals that are kind of 'pin-up' species, superstars that will help people to care about that particularly habitat. I think Percy is great for that. He is an intelligent and characterful fish that uses tools. When I think of the Great Barrier Reef – and its future - Percy will always stick in my mind.

Interview by Terry Payne