Basilosaurus are unaffected by their grab. Just go in with a high lvl basilo and its an easy kill to gather black pearls.
To tame use a plesio or mosa or turtle with about 15k hp and some armor and have your tribe mate stay on till youve fed it. Then swim up and have your mate dismount and also swim up. Keep the bait on follow and the tuso will most likely let go. Wait for about 7 to 10 minutes. Force feed your bait and go back in. Very easy with 2 people. WEAR flippers!
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