I was curious if there was a pattern, so I tested the bite-fight-bite-fight theory. I dived at Blue Hole, where I swam from diving bell to the bow of the wreck (what prankster designed a cartoon lion as a figurehead???) then down to the top of the broken mast to meet the first shark.
First he bit me and swam away, then he came back and fought me. Rough fight. Used the crossbeam at the top of the wreck to boost back to the diving bell. Once at full health I went back and did it again.
So far I've had 20 fights with that first shark, and I'm averaging two fights before I have to return to the diving bell for air and healing now. Every single time it's the same tho, no matter what side of me the shark is on, whether I'm swimming or drifting, holding down Counter or any other key... The first encounter is always a bite, the second one always a fight. If this pattern breaks, I'll post here, but if I get to 40 fights and the pattern hasn't broken yet, I'm calling it.
Bizarre observation : although the sharks in the blood cloud between the two halves of the wreck are CLEARLY agitated, the blood cloud you leave behind when you survive a shark attack, seems to have no effect. The cloud dissapates to quickly to stack two clouds from two fights, but that might be an interesting experiment, if someone's in the mood. :)