Make a trap in the ocean which allows you to take a turtle close enough for it to grab, then feed it 50 black pearls and swim to a safe distance, make sure ur turtle is on passive and following you. It can be fed every 13 minutes. I have found that on official u need to stay in loading distance of the tusto at all times or it will glitch out of your trap
You need two people, one for feeding the black pearls and the other to feed the turtle that is in the grasp of the Tusoteuthis, with sweet vegetable cake for the health and to feed it stimulates berries as well
Just tamed a 150 on an official server. Building a trap high off the ocean floor works great just trap it and rotate out 150 tamed turtles hp pumped. Took about 2 hours with pearls for the tame. Took 50 pearls every 5-10 min. Happy taming!