Everyone, just go to the island, south cave. No need for anything special. Clear the cave and water, dive in and tame the one's on the bottom of the water. They don't aggro unless you hit them.

(Scuba helps, the piranha will jump out of the water and kill themselves, sarcos cant fit into the artifact hallway all the way. Lure and kill them both to clear the water.)

If it helped, lemme know. Cheers.

-MDLostReaper