Hod would you export an island as an XYZ ile from a whole coastline XYZ line?

LoPiret

Dear Global Mapper user,

I have imported an XYZ file (lon   lat   depth (all zero)) of the coastline of a fjord region.

What i would need is the coastline the islands each in a separate XYZ file.
How would I do this? 

Any idea (i doesnt need to be elegant) is very welcome,

With kind regards,
Loic Piret