Hey buddy I have some experience with sharks (both bulls and tiger and blacktip as well). Now with tiger shark: they most of the time never charge and are simply as calm as swimming as when they are chewing fish... So if u get to see one of those big beast, my advise is leave the area and dnt panick but also enjoy the sight coz it might be the only time of ur life to swim with one of those magnificiant animals (i've had 2 so far and would love to swim again with them)!
2nd: Bulls: Now those are really the psychopath: Now you can find those that really dnt give a damn about u, and others that will not let u spear a single fish and will get very aggressive toward u (like charge u to almost ram u or stop in the last few feet distance from u). My advise: Same as above: if it gets too sharky then leave... If not, keep a close eyes on them, stick to ur buddies and immediately upon spearing any fish, get it out of the water (over a buoy if no boat available).
3rd: Blacktips: now those are the ones that enlightens my dives
. I consider them like nice puppies, especially that the ones we get to see are mostly juveniles (1-1.5m) and we rarely get to see the mature ones (2m+) but I've had 6-7 of those "puppies" go into a frenzy within few feet of me to a speared fish (a nice sized trashing and bleeding trevally) that I was just hauling and getting ready to terminate, and within minutes was gone and all i was left were a bent spear. Blacktips are usually not that aggressive (except with speared fish around them) and simply swimming in their direction will fend them off. They dnt school, but sometimes it happens that they show up as more than one at the same time... especially juvenile ones.
Finally most important factor: SAFETY SAFETY AND SAFETY !!!!
I've speared in areas that were 3-4km of swim from the beach with no boat access and whatsoever and both encountered bulls and sharks... Now what was most important was the safety factors: Being 3 buddies carefully sticking to each other and ONLY one spearos shooting at a time.... The reason is that you are most likely to encounter shark after you've speared ur fish (especially after not stoning and shooting those types of fish that go crazy: trevallies, amberjacks, wahoos etc...) as both their blood but most importantly their trashing will attract any shark within the few km circumference of ur area... And for more than once, we had shark showing off right after shooting ur first fish to then disappear and never show up again! So as I said, remember power is in number and with a 110 or 120cm gun, u can even do some serious damage to a 2m bull if needed (though U SHOULDNT!!!!)
Finally: NEVER shoot a shark unless u really feel ur life is completely threatened (and threatened is not like simply having the shark circle u)... U can spoke them if needed (that is they charge u and get too close to u) but dnt attempt at shooting at a 2m bull or 3.5m tiger... U can lose ur gear or worse lose ur life or a limb(remember an injured animal is more dangerous than uninjured, especially if he realizes u r the source of his agony)....
Finally not to worry u: I've never had any major issue with sharks (Apart of a bull ripping off a 12lbs grouper I was holding in my hands, juveniles blacktips going into a frenzy in front of me, and a tiger chomping a a 1.5m cobia my buddy shoot and that i was getting ready to get
) ), but remember, we are intruding their natural habitats and we are not the apex predator... so respect, respect and respect!
Finally have fun, dive safe and tell us of your trip mate !