I know this sounds almost conspiracy theory-ish: just looking at the picture, my first guess is man-made. But I'm almost always wrong.
It just looks really perfectly spaced and each one is the same, in a very mechanical way. With all the talk of snooping on undersea data cables, undersea drones, and the continuance of submarine warfare, it seems possible that this is some kind of undisclosed military drone on either side looking for cables?