Get it with an argentavis, and throw it into a taming pen, than knock it out. Never fight it in the water, it will stun u, and it swims faster than u. It only eats fish meat. If it kills a fish it also gets it into its inventory instantly.
With the ability to go an unlimited amount of time under water this mount is perfect for deep sea diving! 2-4 will make sure you kill anything. Be wary of squids, so long as you have 4 you can still stun him even when he grabs a bary with his tentacle.
By far best dino to tame for deep sea exploration and farming. He's incredibly fast on land, out running taptors, carnos, theriz, etc. His swim speed in water is just as good, with megalodons crumpling to his stun and bite. Great stamina and offense, and you can stay away from base for days with this helpful guy.
This is like an earlier tame of the spino. It's incredibly fast, but can be bola'd and tranqed easily if you're smart about it. Keep in mind that it only eats fish meat (before AND AFTER being tamed) so keep it stocked on that. You can also pick it up with an argentavis despite it looking humorously impossible. Besides that you can do the rest :)