The beached tuso on crystal isles can be tamed you just have to hit it on few times while on your tame and stand infront of tentacles. It will put you through the mesh but when you get off youll pop back up feed pearls and repeat until tamed. Your tame will also pop back up when it lets go
Read this, it might help you:
1: The best place to encounter tuso is 90-91 lat and cover all longitude from red ob to the end of herb Island.
2: Don't solo search, make a party and cover full bottom of the map.
3: Don't search in shallow water and surface, go for mid and deep sea.
4: They need to grab your tame then only can they be tamed.(Take Carbonemys with health and speed pumped)
5: They take 50 black pearls per serving.
6: They only agro in deep sea.
7: Last and the most important, the server must be brutal or their chance of spawning is not that much. Put server to brutal and for one day atleast go killingspree in ocean to open spawn spots for tuso.
8: Pump only melee and health to tuso.
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