Other attempts to explain are feeble at best.
What we do know is that two specific creatures live in the deep. One is the Sea serpent and the other the Mososaur. Neither need to ever come to surface at all.
This represents very good confirmation. We need to get down there and to simply be quiet to observe what must be a biologically rich environment.
"On July 30, 1915, our U-28 torpedoed the British steamer Iberian, which was carrying a rich cargo across the North Atlantic. The steamer sank so swiftly that its bow stuck up almost vertically into the air. Moments later the hull of the Iberian disappeared. The wreckage remained beneath the water for approximately twenty-five seconds, at a depth that was clearly impossible to assess, when suddenly there was a violent explosion, which shot pieces of debris - among them a gigantic aquatic animal - out of the water to a height of approximately 80-feet."
"At that moment I had with me in the conning tower six of my officers of the watch, including the chief engineer, the navigator, and the helmsman. Simultaneously we all drew one another's attention to this wonder of the seas, which was writhing and struggling among the debris. We were unable to identify the creature, but all of us agreed that it resembled an aquatic crocodile, which was about 60-feet long, with four limbs resembling large webbed feet, a long, pointed tail and a head which also tapered to a point. Unfortunately we were not able to take a photograph, for the animal sank out of sight after ten or fifteen seconds."
Submarine captains are not known to be prone to exaggeration, leading to a conclusion that he would not detail such an encounter in any other way but had happened. There would be no known reason to concoct such a remarkable story knowing that most people who report strange creatures are generally meet with only ridicule.
Some investigators have theorized that this encounter could indicate a surviving specimen of pliosaurs or mosasaurs, both of which are thought to have resembled giant crocodiles. The fossil record of these creatures also seems to indicate that their spines were very flexible, which could account for the more serpentine like movement of the creature.