The author is very close-minded and not open to any other theories at all, he does not even take them into consideration. The only theory he mentions is the plesiosaur one, then goes into search efforts.
Personally, I believe that 'Nessie' is a greenland shark, a rare shark that lives at the deepest reaches of the northern oceans, and could easily have been inside the lock undiscovered because of the hundreds of caves that exist under the waters of Loch Ness.
