Captain Nemo is apparently some kind of fish that commands a submarine.
His submarine endlessly roams the ocean in search of his family, but conducts scientific studies along the way, as well as sinking a British warship or two when time allows. This is done because Nemo is an avowed anti-imperialist. This is despite the fact the British Empire now consists of a few tiny islands that nobody else wants. He so far has avoided confrontation with the United States and China and wisely so, since they have gear that actually works.
Captain Nemo carefully avoids land except for his secret base at the northeast side of Clipperton Island in the Pacific Ocean at 109°14 W, 10°19 N. Since his crew is sick and tired of fish and seaweed for every meal, he knows they will mutiny the minute they see a McDonald's or Burger King.