This vast expanse past the Super Drop-Off is almost nothing but pure blue, although there is still life. In the Northern area, you can find striped marlin. In the Southern area, you can find a pod of orcas. If the diver swims down under the orcas, a cutscene will air, and will show a group of sperm whales protecting their calf from orcas. After completing the second part of the Voice of the Night Sky quest, Cameroceras can be seen out past your swimming range at the Southeast (bottom-right) corner of your map.. The Open Sea is also the home of the Leviathan, but only during the daytime. During the night, he is replaced by a Sperm Whale.
The Open Sea is somewhat comparable to the North Coast of Canada's Ice Mosaic, as both areas are largely unbroken expanses of water with uniform surface types and with whales inhabiting them (both white and otherwise). However, the fact remains that they are opposite kinds of habitats. Despite this they have their similarities.