Surfing bottlenose dolphins in South Africa, shown in the TV series Blue Planet 2. Sir David Attenborough is set to return to television for a new series of the BBC’s award-winning series. The seven-part series will mark 20 years since the channel’s natural history unit first set out to explore never-before-seen wildlife in the deepest and darkest realms of the world’s oceans.

Photograph: BBC/Steve Benjamin/PA