If you are being chased by a plesiosaur,then swim up to the surface.like the mosasaur,the plesiosaur does not swim over a certain depth limit and is never seen at the surface(bit weird since they need to breathe,right?)
Not once in all my time on the ark have I seen one alone, there are always two, unless you've already killed one, so watch out when taming, kill one and tame the other or tame both, just remember when you find one that another is probably nearby, ready to tear you to shreds.
I found this guy while riding on my mega I was shooting tranquilizer arrows at two more of these things freaking jumped me!I was like where the heck did they come from!they killed my mega I thought I was gonna get another good tame and till this day their still there I never even went into the water after that I'm basically waiting till they despawn which I bet will never happen unless I kill them myself
A little difficult to tame but definitely worth it! I 100% recommend getting a plesiosaur I tamed a lvl 10 and its stats were very high! But if there're more than one make sure to kill one or separate them!