I wouldn't be worried about the sharks. Your metal tanks are clanging around, so they really aren't that interested in eating you. Humans mostly get attacked because they are on surf boards, and from underneath, they look like sea lions or turtles. The thing that I would be worried about is hypothermia. Old Jakey would never have made it through the night without freezing to death. Wetsuits work by holding a thin layer of water up against your skin. Your body temperature warms that water, allowing you to stay warm. However, the seals around your neck, ankles, and wrists are not waterproof, so your warm water will eventually leave and new cold water circulates in. Water conducts heat at 20X the rate of air, so your temperature will drop surprisingly fast. Without the warming sun at night, and after already spending long hours in the water already, a person will freeze to death for sure.