DOLPHIN ANGELS

I've been reading this book, The Wild Places, by Robert MacFarlane, and every so often there is a paragraph or part that just touches me and I want to share it. Here is today's:
In 2004, a father and son were sailing in the Gulf of Mexico when their yacht was capsized by a gust of wind, sixty miles offshore. They clung to the hull, as it was carried on the powerful currents of the Gulf. After night fell, the water became rich with phosphorescence, and the air was filled with a high discordant music, made of many different notes: the siren song of dolphins. The drifting pair also saw that they were at the centre of two rough circles of phosphorescence, one turning within the other. The inner circle of light, they realised, was a ring of dolphins, swimming round the upturned boat, and the outer circle was a ring of sharks, swimming around the dolphins. The dolphins were protecting the father and his son, keeping the sharks from them.
(p.42)
I read more about this story, as it is an actual true event, on the internet, and learned that the father and son were of great faith. They were out there for two days, and felt strongly that God would take care of them. Here is a quote from the father about their experience:
We made peace with God about it. Ultimately it came down to unless God moved on our behalf, we wouldn't make it in," Ken Heybrock of High Point said. (AP, Charlotte Observer).
My take is that God sent in his dolphin angels. It is pretty amazing that the dolphins would do that. Here are some other stories I found of dolphins saving humans from shark attacks:
http://www.buzzle.com/editorials/11-23-2004-62070.asp
http://www.eurocbc.org/page157.html
http://newsinfo.inquirer.net/breakingnews/regions/view/20081216-178325/Dolphins-save-Puerto-Princesa-fisherman
http://today.msnbc.msn.com/id/21689083

Apparently, it is an occurence that has been reported as happening as far back as ancient Greece, where the first dolphin related human rescue was reported. Very fascinating. I wonder what motivates the dolphins to take the actions they do. Any theories?