It depends on the local laws... but we're building a drone that can fly to a preset GPS location up to 30 kms away and land. On top of the drone is a motion activated camera. The drone can shut down for a preset amount of time such as 24 hours, 48 hours or as long as you dare to risk. Then it takes off again and flies home. I'm also building a motion camera on a tripod that can be delivered by a drone while you move along the beach in a boat for those areas that can be reached by boat but perhaps landing on the shore isn't possible. I'll post again when the project is finished in the next couple of days.
As for thermal camera drones, they have a limited range of 5kms but if thats within your distance needs you could just fly patrols while counting turtles. They're expensive drones to own starting at about $5000 each.
To build one of the autonomous drones that I'm going to release in a "how to build" page is about $400 in parts.