Some one have the answer to this help me. I went to two under water caves and attempted to tame animals. This large under water cave was attached to an above ground crystal cave. Glowing orange and had Bats,snails,acorpions etc. The underwater had sea animals. All the kinds that are hard to find Mozasaurs,Lepluradons,the scary squid. They were all greatly larger than normal and it wouldnt let me tame. Thwy would go unconscience no tame. Food correct in inventory just nothing. Gps 45.5,88.6 Let me know would love to bring home something. Ps bring a pack of Sharks its crazy hard in there.
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.
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
After tamed, you can grapple onto them while a tribmate drives it and easily tame more large water mounts. If you are about to touch a structure or terrain, crouch to take off the hook or you will die instantly and your body will fly across the map
The trick to ko these guys is to wait for them to agro you, once they're close enough, swim up and backwards until you've reached their swim limit and shoot them as many times as possible. When they lose interest, just do the same trick and eventually you'll knock it out