They can't fit through the resource caves' entrances. Just lure it into one and pull out your crossbow/harpoon gun for the knock out. Just be aware of any nearby megalodons, as they can fit into the cave easily and ruin your swimming session.
You can trap a plessi by leading it into a trap the same way u would trap a argi but with the huge hats u only need 3 or 4 n put a smaller one at the end the it cant leave. They can also be found around carno Island FOR MOBILE PLAYERS.
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