One of the coolest pieces of irony about our planet is that the ocean covers most of the surface of the Earth, and yet, the vast majority of it is still unexplored! So, you can bet your bottom dollar that there are tons of unsolved mysteries linked to anything ocean-related.
The Giant Cannibal Shark
In November 2003, a female great white shark, previously tagged by researchers, inexplicably disappeared. According to data from the tag, the fish suddenly dove to a depth of 1,903 feet, and the surrounding water temperature rose from 46°F to 78°F. Apparently, it was a surprise attack.
Given that cannibalism is sometimes observed among great white sharks, scientists seriously believe that the female was simply eaten by another, larger and more aggressive shark.
The Stronsay Beast
In 1808, after a storm, the carcass of a gigantic, unidentified creature washed ashore on the island of Stronsay in the Orkney Islands. Local farmers measured it and determined it was 55 feet long – and that’s without its tail, part of which was clearly missing!
Local naturalists were unable to identify the remains, but later biologists concluded that it may have been part of a giant shark. According to eyewitness accounts, the creature had three pairs of limbs, its ribs were lined with bristles, and a “mane” of bristles ran along its entire back. The bristles glowed in the dark when wet, and its stomach contents were red.
Overall, the creature’s description is somewhat similar to the words of people who allegedly saw the Loch Ness Monster more than a century later. However, the Stronsay monster is described as having a cartilaginous rather than bony skeleton – which clearly indicates that we’re dealing with the remains of a shark, rather than something unidentified.
Kaz II, Dubbed “The Ghost Yacht”
In April 2007, the yacht Kaz II was found drifting near the Great Barrier Reef off the coast of Australia. Everything on the yacht appeared as if the crew was still on board – except that none of the three crew members were!
There were various theories that all three drowned while rescuing one of the crew members, or were kidnapped by another vessel, but to date, no bodies have been found or any confirmation of either theory.
The ocean, the biggest livable space on Earth, covers more than two-thirds (around 70%) of our planet’s surface. And yet, according to NOAA Ocean, most of the ocean remains unmapped and unexplored.
As of June 2025, 27.3% of the world’s seafloor had been mapped. Though this seems like very little, the upside is that we’re learning more about the ocean every year.
One of the reasons why progress can be quite slow is that 90% of the ocean is deep ocean, deeper than 200 meters or 656 feet, making it challenging to map with current technology.
The HMS Daedalus’ Sea Serpent
In 1848, HMS Daedalus was off the coast of present-day Namibia en route to Saint Helena when Captain McQuhae and many crew members saw what they described as a sea serpent in the water.
“The creature passed rapidly, but so close under our lee quarter that had it been a man of my acquaintance I should have easily recognized its features with its naked eye,” Captain McQuhae recalled.
According to eyewitnesses, the creature could’ve been up to 60 feet long and swam at speeds of 12 to 15 miles per hour. Today, some researchers assume that the seamen simply saw a sei whale – but this is far from certain.
Baltic Sea Anomaly
In 2011, while exploring the Baltic Sea floor, Ocean X Team, a company specializing in deep-sea exploration, searching for lost treasure, historic shipwrecks, and underwater anomalies, discovered a strange object 200 feet in diameter, resembling the Star Wars’ “Millennium Falcon” landing on the Baltic seabed.
Even stranger, while the research team was above the object, they experienced interference with the communications system. As soon as they moved a few hundred feet away, everything worked again. Scientists who obtained soil samples claim the object is purely natural. But why, then, was there interference? The researchers have no answer yet.