So from a purely logical stand point, the existence of such a large and ancient creature is unlikely. But assume for a minute that it is possible. What would a plesiosaur need to live in an enclosed lake? Tropical waters: Scientists believe plesiosaurs were warm-blooded. Like crocodiles and alligators, plesiosaurs would need to live in warm waters. The loch is very cold with temperatures averaging about 40 degrees Fahrenheit (4.4 Celsius).
Food: Like other warm-blooded creatures, plesiosaurs would need a large quantity of food. If there is a group of Nessies, then even more food would be needed. Because the loch is full of silt (underwater dust) not much light gets into the deepest areas. So the food chain, which would depend on plankton, is very weak at its base. As a result, there is probably not enough food to support such a large creature.
However, the plesiosaur theory is not the only one. Many other ideas attempt to explain the sightings and "photographs." But two separate sonar surveys of the loch have not found any evidence of a creature larger than a salmon. The last survey,1 completed in 2007 by the British Broadcasting Company (BBC), involved 600 different sonar beams. Using satellite navigation systems, the team made sure every inch of the loch was searched. The team found nothing.

With cell phones and digital cameras, one would think that sightings of Nessie would increase. This has not happened. The BBC team believes the legend of Nessie has endured because people see what they want to see. To prove this, the team used a fence post, raising it before groups of tourists. Afterwards several of the tourists asked to draw pictures of what they had seen drew pictures of a monster's head.
In the article, the author states the theory of the plesiosaur is not logical:

So from a purely logical stand point, the existence of such a large and ancient creature is unlikely.

How does the author imply that other theories besides the plesiosaur are most likely not true? Use evidence from the text to support your answer.