first of all, you're gonna be lucky to see a shark as a diver.
they don't like people and tend to stay away. also, the incidence
of shark attacks on divers is very low (they go for surfers or swimmers).
however, if the brown stuff hits the fan,
-- stay calm. sharks can attack instinctively at sudden movement
-- keep an eye on the shark. sharks seem to avoid going for "prey"
that is looking at them
-- swim slowly and carefully towards the boat or shore. don't get into
unneven or sporadic trashing... this can trigger an attack
if that doesn't work and the shark seems to be going for you, you'll have to
fight back
-- if you have no other choice, use any object to poke, hit, and push on
the shark as it comes near you. target the gills and eyes. the goal is to
let the shark know you're fighting back, not to injure or anger the shark.
if the shark decides to strike, your reflexes are going to be too slow to
do anyting. if the shark is coming at you slowly, it's probably still trying to
make up its mind as to whether you are prey.
i wish i had a source... these are tips i've gathered over the years from
listening to others