Don't bother wasting sweet veg cakes and risking high level dinos. Get it to grapple your mount, feed it, swim away with your mount on passive and follow, squid will let go after a while, wait above the squids aggro level until the feeding interval is up and then go back to feed it again. Rinse and repeat until tamed. You don't need to stay in the squids grasp for the whole time, affinity won't drop whilst you wait above it.
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
Listen clostly, dont lure them to the surrface or they wont want to be tamed. Second, it takes one 50 black pearl feeding. Third, they have to be holding onto something. DO NOT BRING PLATFORM SADDLES NEAR THE SQUID IT WILL GLITCH OUT.
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!