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That would be better for this purpose than a Go Pro.
Except the motion detector only works out to 12 metres.
You might have to get a video and run it all the time. The cheapest Go Pro has a similar resolution to the best camera on that link and for a similar price.
Don't know about the infra red though.
Many moons ago heard a story about a pro in Pumicestone Passage who had a solution for blokes checking his pots. When he caught up with them they received a 12 gauge cartridge - unceremoniously discharged through the bottom of their boat. Rumour has it one bloke simply calmly placed his foot over the hole - but then couldn't reach the other one that was placed at the other end. He did get a holiday in the big house for his efforts though.
I do agree with the other lads about not getting into a stoush with these lowlifes. I know a few of the objects that get carried in the side pockets on my rig - besides the obvious knives that would make pretty handy weapons and I'm pretty sure my boat would not be the only one with them. A time out may be the least of your worries if you go this way. Smart thing is get some piccy's or even better video footage to make Fisheries job easy for them.