The Plesiosaur - Without doubt this is the most popular candidate among monster believers and the press. The plesiosaur was not a dinosaur, it was actually a prehistoric aquatic reptile which lived in the warm seas which surrounded Scotland 70,000,000 years ago.
The plesiosaurs became extinct 65,000,000 years ago during the great extinction which may have been caused by the impact of huge meteor or planetoid. There is no continuity in the fossil record after that time.
There were several types of aquatic reptile including the ichthyosaurs, which were fish-like in appearance, and many species of plesiosaur. Some had short necks and large heads, others had small heads and long necks similar to the fictitious animal shown here.
If we are going to consider the possibility of plesiosaurs in Loch Ness we must consider how they could have arrived here. Around 12,000 years ago Loch Ness was still within the grips of the Lomond advance of ice and the loch would have been a solid block of ice. No animals at all could have lived in it then and far fetched suggestions that plesiosaurs could have survived in deep freeze until the ice thawed, is pure science fiction.
If plesiosaurs came into the loch it must have happened after the ice retreated when access to the loch would have been easier until the land bounced back from the weight of the ice and the loch's level rose. These creatures, then, must have been living in substantial numbers in the North Sea if a viable community were to become trapped in the loch. If there were large numbers in the North Sea only a few thousand years ago where are they today? This factor alone should rule out the plesiosaur, but there are other factors too.
The question must also be asked, why would plesiosaurs swim into a barren loch with no fish and few nutrients, which is how Loch Ness would have been immediately after the ice disappeared.
The plesiosaur, as we have said, was a creature of warm shallow seas. It may or may not have been warm-blooded, but it is unlikely that it could have survived in the ice age seas and the deep cold fresh water of Loch Ness. This is a critical issue which would rule it out as a candidate.
While there are any number of other factors which would count against plesiosaurs I will only mention one more here. The plesiosaur breathed air and, if it were to somehow survive in Loch Ness, it would need to have a high metabolic rate. These two factors, alone or combined, mean that the animals would have to surface regularly and would be seen often.
The plesiosaur really is not a front runner.
All of the problems with prehistoric aquatic reptiles are equally valid with modern day reptiles. In fact, all modern reptiles are cold-blooded and certainly could not be candidates for a large creature living in the 5o Centigrade or 42o Fahrenheit of the loch.
Giant Squid and Octopi - The class of invertebrates, animals without a backbone, have never been seriously suggested as candidates for the Loch Ness Monster, but it would seem sensible to deal with them anyway as they are real monsters of the oceans.
The existence of giant squid was only proven at the beginning of the twentieth century when a thirty-foot long juvenile specimen was washed up in Nova Scotia. The fact that such large animals living in the sea had not been previously proven could be seen as an argument in favour of Loch Ness Monsters in general, but as candidates there is one serious and fatal flaw in any suggestion of them living in Loch Ness. Anyone who has studied science, whether in an online university or at the highest levels of academia, can see the flaw in this logic.
Owing to Loch Ness being fresh water and the North Sea being salt water, plus the fact that the only way into the loch was from the sea after the last ice age, we can conclude that no large invertebrate could have made that transition.
Small fresh water invertebrates entered the loch on the feet of water birds over a period of time, but this could not have assisted their salt water cousins who would have needed a gradual change in salinity, which certainly did not occur in the case of Loch Ness, to adapt.
Sorry, the kraken does not live in Loch Ness.
All of the problems with invertebrates apply to amphibians with the added complication that there are no large amphibians in the world today.
Frogs and newts can be found in Loch Ness and these have been introduced as spawn on the feet of water birds. Unlike invertebrates, there are no saltwater amphibians, and yet the only way for some unknown giant amphibian to enter the loch would be, as previously mentioned, be from the salt water of the North Sea after the ice disappeared.
It is not possible to completely discount a large unknown amphibian if a way can be found to overcome the entry problem. Could a giant amphibian have sufficiently small spawn to stick to the legs of herons and other birds? If so where did they come from? Why are they not found elsewhere?
However unlikely it may be, a giant amphibian cannot be completely ruled out.
It has often been put forward that the Loch Ness Monster could be some sort of long-necked seal, sea cow or whale, but no such animal is known to exist anywhere in the world and it is now considered that all known large mammals have been catalogued.
There are two other serious problems. Mammals are all warm-blooded, consume vast quantities of food and surface regularly to breath. These factors alone completely rule out mammals as candidates.
I think you're on the wrong web site.
Leaving aside the very, very remote possibility of an unknown giant amphibian, if reptiles, mammals and invertebrates are ruled out, the fish category becomes the only sensible possibility.
There are three feasible fish candidates.
The first of these is the giant eel. For centuries there have been reports of sea serpents in the oceans and there is no practical reason why a huge species of eel should not exist and enter the loch from time to time. The biggest problem with this is that they have never been caught in rivers, lakes and lochs anywhere else in the world.
The second is the Wells catfish which has been known to grow to nine feet (3m), but this would appear to be too small as a surface object.
A far more likely candidate, and one which is found in other lakes, is the sturgeon, a migratory fish which comes into fresh water to spawn. While the Atlantic sturgeon is not known to reach immense proportions, like many fish, they can continue to grow into old age. The biggest sturgeon ever recorded was from a river in Russia. It was 8m (27 feet) long and from the bony scales along the side of its body, its age was estimated at well over 200 years.
The fish shown above was washed up in Lake Washington and was 3.5m (11 feet) long.
Important points in favour of the sturgeon are that they do have a slow metabolic rate, live deep, but occasionally surface. They are known to live in other lakes and some specimens, like the one in Lake Washington, have been known to live out their old age in fresh water.
Against the sturgeon is that the European sturgeon is not known to spend long periods in fresh water and the regular return of a giant sturgeon to Loch Ness would seem unlikely. The lake sturgeon is a different species and not found in the UK. Perhaps European sturgeon could adapt to fresh water, but that is not known.
There is one interesting sighting of a monster in the River Ness back in the nineteen-thirties. The lady concerned described a huge animal which resembled a crocodile with tusks swimming up the river towards Loch Ness. This description could well be applied to the bone large-scaled back of a sturgeon when viewed from above. Interestingly the sturgeon also has long barbels under its mouth which could be interpreted as tusks if the fish were wallowing. There are no other records of sturgeon in the river or loch although they have been found in the Moray Firth into which the River Ness empties. Another, but unsubstantiated report, is that one was caught in the River Garry. Any sturgeon found here must have come through Loch Ness.
The sturgeon may well be the most likely candidate for the Loch Ness Monster, but they are certainly not a very romantic solution. Who would come all this way to see the Loch Ness Fish?
One thing is absolutely certain. If a huge sturgeon is ever caught in Loch Ness, people will not accept that it proves the monster is just a bigger one. They will probably just wink, knowingly, and say, "Ah, so that's what Nessie eats!"
We shall see.