I found this old map. ( sounds like the opening line to a treasure hunt), from before the Coquet changed course(I think, maybe not but looks like it), and you can see an island shaped like a monkey. A few houses/buildings are shown. I've just had a long and interesting phone call with my mum about this but no real conclusions. When we were little, Monkey Island was the rocks where the old Dredger sank between the Jumpy Shore and Coquet Island , there used to be a large pole there, at a really low tide, you could see the wreck. Anyway, here is the map, well a little chunk of it. There's definitely a monkey shape there if you look for long enough.
https://db.tt/ax7cVQYJ