But he is not treading water he is pushing people under to used their buoyancy as a life preserver. Each one is only good for 5 minutes before they fully exhaust their air and therefore buoyancy. He only has 10 more living people in sight that he can use and he knows the closest boat is the Carpethia and that is 4 hours away. Yes it is an act of desperation because logically his actions have no chance of saving him.