Take a low lvl turtle and tame it, raise it's O2 and health until it's max lvl, then saddle it up, and bring a tribemate with you so that your turtle does not die and you can tame the giant squid with ease.
Use a Mosa to tame this beast. Let the Mosa get grabbed wait a couple seconds get off feed it black pearls. Have your mosa on follow lowest, swim a bit away from the Tuso after feeding it, when the Tuso lets go the Mosa will swim to you. Repeat until Tuso it tamed. Super easy!
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