Aquabatics.

That’s a dolphin balancing on the head of a hump back whale. Prize-winning photographer Lori Mazzucca writes:

I was observing a strange interaction between a pair of bottlenose
dolphins and a humpback whale, when it became apparent that the two
species were collaborating in some way. The dolphin was lying on a
humpback whale’s head while it was slowly swimming along. Looking
through my camera lens the stunt appeared to be orchestrated by mutual
“agreement.” The whale very slowly—and vertically—lifted the dolphin
into the air. I expected the dolphin to wriggle atop the humpback’s
head to get off, but it just laid still and arched, trying to stay on
top of the whale’s snout. In this frame the dolphin was beginning its
slippery return to the sea. Once back in the ocean, the dolphin swiftly
swam away with the other dolphin, leaping joyfully as if they had just
scored a coup! Smithsonian Institute