You might want to wait until 13th August to look into this mod, cant really give a lot of advice right now as dev kit is still lack of some data needed to make this mod possible
I would think you would need to have a range check around your object, if anything get in range, check if that object is primal dino, and is underwater → then grab that object and trigger some random event that if it’s happen to be true, make your bait the new target and force them to move closer to that rod (and maybe some % change to break your rod as well)
Dont think the data to check that if dino is underwater is available now - as least i cant really find it