Apparently there have been numerous instances when dolphins have protected humans from sharks.

It has been so prevalent that in some circles it is believed that where there are dolphins there is no danger of shark attack. Unfortunately this is not true. While dolphins are able and sometimes willing to protect humans from sharks, they may not.

Interesting thing. What exactly does it tell us about how dolphins regard us? That they think some of us are worth saving and some of us not worth the effort? Or that some of them will save us and some of them won't be bothered?