I would (before anyone got on the platform) cut the rope and sabotage the whole affair.
I'm very much against F-ing with Great White sharks. Recently a guy got bitten in half (a surfer) in Australia while a little farther out some jerk was chumming the water so that tourists could see the sharks. And the guy chumming (using blood) wanted to blow the whole thing off as a coincidence. Maybe, but that's one hell of a coincidence.
Leave the darn things alone. It's one thing to be out there in a boat where they naturally feed, and perhaps you'll get lucky and shoot one (hopefully with a telephoto from far away so as not to disturb them) as they feed, but don't dump blood or fake seals in the water. That's just ignorant. Just get out there, give them space, and wait patiently. That's why they invented alcohol and ear buds. You sit all day with your buddies, drink some beer, and aim your camera. As long as the captain is sober and you aren't teasing the animals (or throwing trash overboard) no harm/no foul.
But if you like dragging plastic seals through the ocean you might as well drive a Jeep through the Savannah dragging a large, plastic zebra so that you can see Cheetahs or lions chase them. It's pretty much the same thing, and it's not cool.
That's my opinion as someone who has spend countless hours in the ocean from about the age of seven, surfing, diving, swimming, relaxing, etc. I always have a bit of fear about sharks, but that will never stop me from enjoying the water. I just have to accept that I'm a step lower on the food chain out there, but I don't need some jokers reminding the sharks that they are hungry. Plus, it takes a lot of energy to chase down and attack that "seal". So the shark gets a piece of plastic?
What's next, remote-control mouse in a field so you can tease the hawks and get a good photo?
If you want to do that kind of thing, just use the old fishing string and dollar bill trick and watch some guy run down the sidewalk chasing money.