Ride a tamed Ichthyosaurus close to the Shasta that you want to tame, it will start following you, after that you need to go to the surface and the taming progress will start. Once up top the surface, dismount to allow the Shasta to communicate to the Ichthy and use a Sickle to remove three leeches indicated on the sides of the Shastasaurus, the player will only have 30 seconds (For every domesticated Ichthy nearby up to 3) to complete this task or the Shastasaurus will lost taming effectiveness. After remove the three leaches the Shastasaurus will require feeding, so the player needs to swim closer to the mouth and feed it having the taming food on the last hotbar slot such as Extraordinary Kibble or Fish Meat. Repeat this progress until the Shasta is tamed.