auv-ee
May I add to your remarks that ROVs are somewhat limited. They do not (usually?) work from a direct tether to the surface ship. They are lowered in a cage and turned loose with a tether back to their transit cage. The tether's length is limited. So their ability to move along in a search is limited. They'd have to search an area and come back to their cage to be moved to the next block lest cords get tangled.
They're ideal for working on drilling rigs. For wide area searches they would seem, to me, to be somewhat limited. (And I wonder when they will grow binocular vision.)
{^_^}