Oceans cover 70% of Earth’s surface, and remain almost entirely unexplored.
Are they home to still unknown sea monsters?
Gustav Paulay, curator of marine malacology, Florida Museum of Natural History:
There is a good chance that some pretty large animals remain undiscovered in deep oceans. A good example of this are the beaked whales, a group of cetaceans that is hard to encounter and new species keep getting discovered. An especially cool example is an undescribed beak whale that is being eaten in the Kiribati islands (see here).
Large invertebrates are commonly found of course, but few are giant squid sized. I would think that large fish could remain undiscovered; the megamouth shark was a good example of that a couple of decades ago.
Timothy Essington, professor of aquatic & fishery sciences, University of Washington:
Given the vastness of the ocean, I would not be at all surprised if someday some intrepid explorer discovered some bizarre new form of sea life that we never thought possible. It might be some creature of enormous size, a radically new body design, or some unique way that it “makes a living.
Paul Yancey, professor of deep sea biology, Whitman College:
The answer is: yes, it is possible. The key point here is that humans have only surveyed perhaps 5-10% of the oceans, and even lower percentage of the deepest oceans. New species are being found all the time, some of them fairly large. In fact, new species of whales, very large animals which live at or near the surface, were found as late as the second half of the 20th century. The giant (6-ft) Riftia tubeworms of hydrothermal vents were discovered in 1977.
Stephen Palumbi, professor of marine sciences, Stanford:
Where are the truly huge specimens, like those Captain Nemo fought on the deck of his Nautilus? It is possible that exceptional individuals exist, somewhere in the ancient blackness beneath the planet’s seas, hidden under ice caps, or among the volcanoes of the vast Pacific. If a creature grew beyond the strength of the largest whales, no mysterious squid beaks would appear as gastric evidence of the existence of a third giant squid species. If it lived its life in the hidden vastness of the deep sea, avoiding submarines, we’d have no way to know about it. Imagination will always tempt us more than reality: we’ll always draw monsters on the margins of maps.
In overall, the ocean is vast, and much of it remains unexplored. Large new creatures are still discovered on a fairly regular basis. Are undiscovered sea monsters still possible and plausible? Absolutely. Source