Petras is part of the escort for the siege turtle hatchlings during the Gyala Hatchery mission. He is the one who will give you three Smoke Canisters that are used to direct the attacks of the Siege Turtles.
After completion of the mission, he can be found in the Leviathan Pits and offering the next primary quest.
In the Leviathan Pits:
- "I grow weary of this place. We Luxons are not meant to stay in one place for too long..."