They were just metres away from one - weighing 40 tonnes – when it extended its giant flipper towards them. The 18m whale, longer than a doubledecker bus, seemed to be shaking hands!
Photographer Masa Ushioda took the pictures: "This particular female humpback was extremely friendly and very curious. She extended her pectoral fins to us repeatedly and sought for physical contact."
The female blew bubbles to keep amorous males back, while she communed with the divers.
Ushioda: "It was like the explosion of an underwater bomb. Seawater is over 800 times denser than air, so the impact of the sound wave was amazingly loud."