So, the button idea had been floated around this house before. My main objection to it was that there were buttons just like that in the era, but that they had holes though them - otherwise they don't stay on - and they generally aren't as ornate. I'll still bring it up as a possibility, though.
I like the fishing implement idea more and more.What irritates me is that the dang thing looks so familiar, but I can't place it in its context. I have a vague recollection of seing something like it when I was a kid, but I can't remember where or when.
I am not too sure about the context that it was found in, other than it is in the harbour and that it's a Norse harbour (i.e. viking age).