Tim Mellon,
In the image you've posted in your Reply #2 above, you say you are seeing a cable/wire on the left and a cable/wire on the right. Have you even considered the possibility that what you're calling the cable/wire on the right isn't a cable, wire, or rope at all? Have you even considered the possibility (I would say likelihood) that it is simply the shadow of the higher portion of the coral/rock ledge pretty distinctly visible in the the lower right portion of the image. The shadow of the upper part of the ledge is being cast on to the lower part of the ledge. Note how your right-hand "cable/wire" bends as you approach the lower right portion of the image, and this bend matches the bend in what pretty obviously to me is the face of the rock/coral ledge. Your right-hand "cable/wire" is actually this shadow.
Frankly, looking at the left-hand cable, it's not so obvious that it is a cable at all, either. It could be the shadow cast by another small step/ledge in the rock.
Evaluating where the light source is in an image and evaluating the resulting shadows is very important in analyzing an image. How do I know this and know to be wary of shadows that might look like physical objects? I have looked at hundreds of underwater images from electronic still cameras and still captures from underwater video cameras, all taken using artificial light. I work with a group of people who collectively have looked at tens of thousands of such images. They all agree with me that what you see as a "cable" on the right side of this image is really a shadow cast by the rock/coral.
Jeff P.