This has been studied in several countries but the best information comes from the natives of the Tuamotu Archipelago in Polynesia, where freedivers in the past made 40 to 60 dives a day to depths of 100 to 140 feet to gather pearls. Their descents were assisted by a lead weight and they ascended by pulling themselves up a rope tethered to a collection basket. An assistant then raised the basket to retrieve the shells gathered on the bottom. Descent times were 30 to 50 seconds, total dive time, about 100 seconds and the surface interval between dives was four to six minutes. Many of the divers developed a severe illness called Taravana, the symptoms of which are similar to those of decompression sickness-paralysis, visual changes, hearing loss and dizziness. Some divers died.