Ahh, so if the monster exists then it must, like the porpoises, only rarely travel to Loch Ness from the ocean, so that few sightings per century can be expected.

I thought all alien craft sightings were BS until four separate Navy pilots came forward to say they all saw that white tic tac in 2004. And three of the four pilots have done television interviews, most recently this 60 Minutes one:

https://www.youtube.com/watch?v=ygB4EZ7ggig

If not for the link between Loch Ness and the ocean I'd think the existence of the monster could probably be ruled out as attention seeking liars. But now that we know porpoises sometimes make the rare trip from the ocean, we can't 100% rule out the monster never does. Does Dochfour Weir have 24/7 thermal and sonar monitoring and recording? Would Dochfour Weir capture on video and count every single porpoise that passes through at 3am, 365 days per year?

You may mistake my post for suggesting Nessie doesn't exist. All I am getting at is, if there's a large animal the size of a whale migrating down to the loch, over a few hundred migrations since the weir was built, someone probably would have seen it. Therefore, the migrations, if they happen, most likely are a rarer event.

On the flip side, the existence of porpoises, while interesting, does not prove the existence of Nessie. It simply makes more room for the possibility.