I want to preface this post by reminding people there are close to 400 species of elasmobranchs, and only a very small number grow to a size big enough to do any harm to a human. Most are cold water animals that stay smaller than 4 feet and feed exclusively on inverts and small fish.
I want to touch on two things quickly.:
First, the Indianapolis going down and turning into a shark story is nothing more than a story. Loss of life due to actual shark attack has been dispelled. Less than 10 people MIGHT have been taken by sharks. Sailors seeing sharks in the water turned into sailors 'seeing' sharks eating people. Remember the time frame - back then people knew very little of shark behavior, and they were seen as man eating monsters of the ocean. That image was burned into the heads of many of those young men prior to that night.
^ what about that somewhat famous video of that guy explaining how he's not in any danger as a bull shark(?) swims around him in shallow water.. and then BAM! it latches onto his leg taking massive chunks....the shark clearly knew that he wasn't "normal" prey....he wanted to bite him and did.
Dr. Erich Ritter is the man in the video you are talking about. He will tell you there were several factors at play. 1) They got too comfortable with the sharks around them, and weren't paying attention. They missed the cues that the sharks were investigating them more and more. 2) They had their hands in the water. Get in the water and watch hands waving. The white flashes when the sun hit's the palm looks very similar to schooling fish (food). What we see in that video is a great example of an investigatory bite. That bull bit and let go. Had it wanted to, it would have latched on, pulled him in and finished the kill. It did not, nor did the other sharks join in.
Let's step back and look at this from a different angle.
Shark 'attack' lends itself to a negative context right of the bat. It sounds like sharks are aggressive toward humans. In fact, the term should be shark investigatory bite. Sharks have amazing sensory abilities in the water, probably more that we as humans have on land. Prior to a bite, a shark will make several passes and figure out what an object is to the best of their ability. After that, it will bite. Why? There are there are two reasons. Sharks will bite as a means to capture prey. If they bite, they are going after a food source. Hunting in general takes a lot of energy. Sharks won't waste that going after something that won't restore the calories burned (which is why they tend to prey on sick, weak, injured animals). The second reason is to investigate further. If they can't ID an object, they will bite it to figure out what it is. This is why you hear about sharks with odd objects in their stomach/GI tract. If sharks saw humans as a viable food source, no beach would be safe for us - ever. They would have keyed into our patterns of playing in the shallows many decades ago, and been right there hunting the whole time. In fact, most people in the water have no clue how close sharks really are to them - and yet the shark swims by without the human even realizing one was there.
Humans are NOT a naturally occuring object in thier world. They aren't seeking us out as food. Sharks are smart and can be very curious. When they bite a human, most of the time it's trying to figure out what we are. Sadly, the sharks that will do that are big enough to cause fatal damage to the human body.
As someone who has been bitten by several species of sharks, I can assure you none of them fall into an aggressive / eat a human classification. They were wrong place/wrong time accidental bites - whether is be getting between a food source and the shark, missing signals and cues from the animal or the dumbest one of all - the "SFE" (stupid feeding error).
In my 20 years of dealing with sharks, I have never witnessed a shark waste the engery it takes to bite as an act of pure aggression.