While they have a lot of health they are stupidly usless to fight back attackers, needless to say overrun them; Specially in water where every 10 feet theres 3 f*cking eels, 5 sharks and 2 mantas comming atcha.
Avoid running into fights as much as you can or always have a couple badass tames or tribemates following you to clean up attackers, otherwise you will be struggling for your tame's life as well as everything you brought with it.
Tamed you'll be able to build on its back. When diving he provides an oxygen bubble on his back allowing you to submerge your base on the floor of the ocean.
Are you turtley enough for the turtle club?