PALMAS, Brazil—Summoning skills passed down from his Indian ancestors, Ricardo Waerokrá fired his arrow on a recent day at the hand-drawn picture of a fish, hanging on a pole some 30 yards away. He hit the fish, but Mr. Waerokrá was not satisfied.

“I missed the head,” murmured the muscular 40-year-old, who learned to hunt fish from his father.

This...