There has long been a superstition among mariners that porpoises will save drowning men by pushing them to the surface, or protect them from sharks by surrounding them in defensive formation. Marine Studio biologists have pointed out that, however intelligent they may be, it is probably a mistake to credit dolphins with any motive of life - saving. On the occasions when they have pushed to shore an unconscious human being they have much more likely done it out of curiosity or for sport, as in riding the bow waves of a ship. In 1928 some porpoises were photographed working like beavers to push ashore a waterlogged mattress. If, as has been reported, they have protected humans from sharks, it may have been because curiosity attracted them and because the scent of a possible meal attracted the sharks. Porpoises and sharks are natural enemies. It is possible that upon such an occasion a battle ensued, with the sharks being driven away or killed.
Whether it be bird, fish or beast, the porpoise is intrigued with anything that is alive. They are constantly after the turtles, who peacefully submit to all sorts of indignities. One young calf especially enjoyed raising a turtle to the surface with his snout and then shoving him across the tank like an aquaplane. Almost any day a young porpoise may be seen trying to turn a 300 - pound sea turtle over by sticking his snout under the edge of his shell and pushing up for dear life. This is not easy, and may require two porpoises working together. In another game, as the turtles swim across the oceanarium, the first porpoise swoops down from above and butts his shell with his belly. This knocks the turtle down several feet where another porpoise is waiting to give it another butt. The turtles seem to enjoy it, but perhaps they would not if they could feel the scratches on their shells from the porpoises' teeth. After such a burst of activity they usually take a short rest before they start off again.
A porpoise will follow a ship for hours at a time, leaping out of the water and doing somersaults. There is no evidence that porpoises have a language but they communicate with one another by squeaks, clicks and whistles. It has been suggested that they may be able to communicate with humans through these sounds, but this has not been proven. One theory is that they use these sounds to navigate, by detecting the echoes of their own voices. Another theory is that they use them to communicate their emotions, such as excitement or fear. Still another theory is that they use them to identify one another, as each porpoise has a unique set of squeaks, clicks and whistles.