Scuba Diving/Can a person survive a free dive (no oxygen) of 350
QUESTION: Can a person survive a free dive (no oxygen) of 350 feet if a trained dolphin takes the person down and back up?
ANSWER: Physiologically? Yes it is possible.
Humans have been to just over 700 feet of sea water (214 M) during no record apnea attempts.
This normally involves riding a weighted sled to depth and then riding a inflatable lift bag back to the surface on a single breath hold.
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QUESTION: Would most people be able to survive that? Would most people who are stranded at see with no live jacket be able to hang on a trained dolphin for hours, when the dolphin is taking this person to land. If the person less go of the dorsal fine the dolphin comes back.
In my opinion no, not without a natural physiological advantage and a lot of specialized training. These are world class athletes performing free dives approaching these depths.
As for the dolphin scenario I am afraid I do not have adequate experience to make an informed comment.