So, there is the question again. Does a 22 mile lake have enough fish and mollusks to sustain a population of plesiosaurs for yrs? Thousands of years? And without a noticeable drop in food supply? And feeding the local human population without being noticed as well? And feeding other fish predators as well?
there is a famous paper published as a tongue and cheek article (Ryder was the author)in one of the zoology journals that we read when I was in 4th year university (I have a bio degree) and it looked at exactly that:
does loch ness have enough of a food supply to allow a large enough population of plesiosaurs to live?
the answer was no. loch ness is oligotrophic and not very productive.
not enough food in it to sustain a breeding population of predators that large.