Is there a myth that dolphins were humans who chose to return to the sea?

Question

In the Fantasy Island (1998) episode "Dreams", Michael Allen is a stockbroker who finds a mysterious woman (played by Jennifer Garner) who says this to him when they first meet.

Sally: You know, there's a theory that dolphins were once human beings who chose to return to the sea. That would explain it.

Michael: Explain what?

Sally: Why they have such a close connection to people.

As it turns out, "Sally" is indeed a dolphin who can transform to a human.

This sounds like the sort of thing that would be in a myth or traditional stories (although her phrasing it as a "theory" is a little strange). Are there any myths or stories about dolphins being humans who chose to return to the sea? Or is this something likely made up for the TV show?

Answer 1

In Ovid's Metamorphoses, book III, there is of course the story of the Tyrrhenian pirates that Bacchus turn into dolphins, but it's against their will, and as a punishment for betraying him.

Here is a translated extract of their transformation (the narrator at this point is a fisherman called Acoetes):

And Bacchus in the midst of all stood crowned with chaplets of grape-leaves, and shook a lance covered with twisted fronds of leafy vines. Around him crouched the visionary forms of tigers, lynxes, and the mottled shapes of panthers.
Then the mariners leaped out, possessed by fear or madness. Medon first began to turn a swarthy hue, and fins grew outward from his flattened trunk, and with a curving spine his body bent.—then Lycabas to him, 'What prodigy is this that I behold?' Even as he spoke, his jaws were broadened and his nose was bent; his hardened skin was covered with bright scales. And Libys, as he tried to pull the oars, could see his own hands shrivel into fins; another of the crew began to grasp the twisted ropes, but even as he strove to lift his arms they fastened to his sides;—with bending body and a crooked back he plunged into the waves, and as he swam displayed a tail, as crescent as the moon. Now here, now there, they flounce about the ship; they spray her decks with brine; they rise and sink; they rise again, and dive beneath the waves; they seem in sportive dance upon the main; out from their nostrils they spout sprays of brine; they toss their supple sides. And I alone, of twenty mariners that manned that ship, remained. A cold chill seized my limbs,—I was so frightened; but the gracious God now spake me fair, 'Fear not and steer for Naxos.' And when we landed there I ministered on smoking altars Bacchanalian rites.

Answer 2

Are there any myths or stories about dolphins being humans who chose to return to the sea?

I've long suspected that dolphins are the real subjects of Mermaid mythology. And I wouldn't be surprised to stumble across some obscure myths following more specifically along that line of reasoning.

Currently, I would just like to present this little tidbit gleaned from traditional Cherokee Cosmogonic Myths (c1902, by American Ethnologist, James Mooney; p239-40):

IV – THE MYTHS

Cosmogonic Myths

I. How the world was made

The earth is a great island floating in a sea of water, and suspended at each of the four cardinal points by a cord hanging down from the sky vault, which is of solid rock. When the world grows old and worn out, the people will die and the cords will break and let the earth sink down into the ocean, and all will be water again. The Indians are afraid of this.

When all was water, the animals were above in Gălûñʹlătĭ, beyond the arch; but it was very much crowded, and they were wanting more room. They wondered what was below the water, and at last […]

The Cherokee believed that the whole earth was covered with water at one time. All animal life, including humans, lived up in the sky (Galunlati). Presumably then, they were disembodied spiritual entities (like souls, or ghosts), while inhabiting the air.

It wasn't until after the "Beaver's Grandchild" (the little Water Beetle, aka Dayunisi) went below the water and brought up mud to build dams resembling islands and providing dry land on which the other mammals could walk, that they were able to leave the sky vault and live on the earth.

Furthermore, they realized after settling from the sky onto land, that:

There is another world under this, and it is like ours in everything – animals, plants, and people – save that the seasons are different. The streams that come down from the mountains are the trails by which we reach this underworld, and the springs at their heads are the doorways by which we enter it, but to do this one must fast and go to water and have one of the underground people for a guide. We know that the seasons in the underworld are different from ours, because the water in the springs is always warmer in winter and cooler in summer than the outer air.

They describe a world of water, with streams for trails. Entrance to that underworld is made through spring heads.

But in order to visit that world, one is required to:

• Fast (lose weight)
• Go to water (physically get into the water)
• Allow yourself to be guided by one of the underground people (follow them)

They spoke about it as if it was at least fairly commonplace to desire to go there, if not succeed in doing so.