I saw a BBC documentary where a guy called Gordon Buchanan - wildlife camera man and filmmaker spent weeks with a family and community on a tiny island in the Polynesian islands and they were a fish catching community with the majority of meat coming from the sea mixed with pigs and chickens they kept in small number.

Aside from the fisherman taking then that the fish stocks and numbers had gone vastly downwards in their life time, they were only in their late thirties early forties. These guys would use basic spear propelled via elastic tubing with home made goggles and they would be off lobster hunting for 6, 7, 10 minutes at a time under water and the longest he witnessed was 13 minutes without resurfacing for breath. They were so adept to the sea from such early age that their blood had adjusted with low amounts of oxygen or build up of nitrogen, something like that. Somebody better knowledge can explain the science behind it hopefully.