Me and my buddy just tamed a 145 by building a trap against our north tropical bubble. From there you can actually reach the plesiosaur from the inside and tame it using darts to speed up the torpor process. From there it's just a waiting game. You can pretty much use any trap that you can use for wyvernd. Behemoth gate frames and one gate or conservatively use one gateway and door and pillars and ceilings staggering it down so that if it swims more towards the bubble it'll be way easier to hit
If you want to tame one I recommend using a icthy because I tamed one by using it. If you are try to pump up its stamina and speed. But obviously if your not like your a sarco master like me🐊🐊 you can use that. Use a crossbow and tranq darts or toxiant arrows because it reloads faster and guns don’t work underwater. Trust me I tried it. It didn’t turn out well. After like 20 tranq arrows it will be unconscious then get somewhere near 10 raw prime meat and BOOM!! You have a plesiosaur /\ if this helped
There is a glitch at the redwood on the center, where plesiosaurs will spawn really near the coast and whole groups of 2 or 3 are glitched in the water, meaning you can knock out multiple plesiosaurs at the time.
My trusty sarcosuchus made knocking my plesi exceedingly simple, for three reasons. The sarco is fast, it ascends quickly, and you can shoot from its back. Once I separated my plesiosaur from her friend and killed it, the procedure was simple. When the plesi reaches a certain height it begins to flee. I dragged her up then filled her with tranqs until she aggro'd again. Repeat process until unconscious. Simple with sarco.
The trick is to argo one, have him chase you into an underwater cave where he will not be able to fit through the door but his long neck and head does. when you do this he will not de-agro, you can then get a clear shot from the cave with a bow and tranq arrows