Crusoe said..
Maybe we could make a list of ways to enhance the chance.
I always thought "swimming at dusk with a dog" was a good one, but "wrestling each other on the surface whilst snorkelling/swimming" might just beat it.
I've also order the book you recommended Bara, cheers
Actually theres no correlation between time of day and attacks in Australia. But we are still told to be wary of dawn and dusk because " well we have to say something" according to one official interviewed in the book

I reckon there's a false sense of security when on tour groups like this one. Just look at the whale shark diving off exmouth where groups of people happily jump in and thrash around offshore whenever the tour operator says so. Would never do it yourself off your own boat there but human psychology is pretty interesting on this stuff. There's a chapter on that and how we perceive risk etc.