Really no need to fret about attack by a shark. Here's an orientation to the topic from my "Ask RSD" column in the Mar '00 issue of "Rodale's Scuba Diving" that will also answer your question about what consistitutes aggressive behaviors:
"Do need to worry about sharks while diving?"
While statistics are not fully reliable and vary substantially across time, over the years 1990 through 1997 an average of about 9 unprovoked attacks per year on divers were reported worldwide. Slightly less than 20% proved fatal. In other words, out of the millions of dives done worldwide in each of the last 8 years, on average less than 2 divers per year died as a result of unprovoked shark attack. Death by lightening or a vending machine falling on you is far more probable. Furthermore, these attacks were much more likely to occur in some areas than others. The most numerous attacks on divers occur in the continental US, Australia and Africa (2/3rds in the Republic of South Africa), respectively. Within the US, Florida and California account equally for the majority; Hawaii has less than 1/4 the total of these two states. The Caribbean is low on the list.
Sharks, about which much remains unknown, are among the ocean's most fascinating and maligned creatures. Around for hundreds of millions years, they have changed little in the past tens of millions. The approximately 370 living species range in size from the 6" carnivorous juvenile Dwarf Sharks to the 45+ plankton eating mature Whale Shark.
Sharks are fearsome predators due to marvelously acute sensory systems, including the ability to sense infinitesimally weak electrical fields, very low frequency sounds such those generated by escaping and struggling prey, and a sense of smell which can detect a single drop of blood in one million drops of water. While vision tends not to be nearly as well developed, some sharks have excellent sensitivity to contrast and motion, and low light acuity.
The majority of sharks pose no threat to man; only about 42 species have been implicated in attacks worldwide. Great Whites account for the majority, and these are often believed to be cases food confusion; humans are not at the top of the menu with high fat animals like seal and sea lion. Next in order are the Tiger and Bull, who some feel aggress just because the diver is in proximity.
Most shark attacks occur from below or behind and are unseen by the diver, although prior to an attack is it not uncommon for them to make increasingly closer passes, or even bump you. Sharks within the line of vision also may signal they are disturbed. This commonly takes the form of an S-shaped posture, with arching of the back, lowering of the pectoral fins, & movement of the tail to one side, and sometimes shaking of the head from side to side--you'll recognize it. If you observe this, return to the boat if possible; if not, slowly sink to the bottom or back up against a reef or wall, and remain motionless. If a shark approaches you very closely, purge your second stage in front of it, then hum deeply or yell into it. If you have no other recourse, such as when a shark starts bumping you, bang it on the snout or gills, but if possible do this only with a gloved hand or arm, or inanimate object. The skin of many sharks is quite rough and could easily draw blood from an unprotected body part. A number of protective measures have been experimented with, including certain chemicals and electrical shields, but none has proved infallible.
You can reduce the already very tiny odds of attack by: (1) not diving near fishing, and especially spearfishing; (2) diving in groups; (3) avoiding deep channels and shallow water which rapidly becomes deep; (4) not diving at dusk, dawn or after dark; (5) avoiding shiny jewelry and exposure suits with contrasting colors; (6) avoiding murky water; (7) not harassing a shark; and (8) quickly returning to the boat when a shark becomes overly inquisitive or postures.
A diver following the above suggestions has no reason for fear."
On the UNEXSO shark feeds, aggressive types like great whites, tigers & bulls will not appear. They will be Caribbean reef sharks, and all or nearly all females. To the best of my knowledge, and I track this, no diver on a UNEXSO feed has received more than an apparently inadvertent bump.
Have fun.
DocVikingo
