In which of the oceans is the fauna of the least diverse? In what latitudes do sea turtles live?

In which of the oceans is the fauna of the least diverse? In what latitudes do sea turtles live? In what latitudes is herring common?

Of course, less diverse fauna in the cold Arctic Ocean. As a rule, most sea turtles live in tropical latitudes. But the herring lives in the northern latitudes. But in the Arctic Ocean, for example, a humpback whale lives. It is also called simply humpback. It belongs to the Polosatikov family. It is also worth knowing that it was named so because of its fin, which is located on the back. It is this fin that resembles a small hump. Also, this whale arches its back very much.