This is a bit of a geeky post, but the Fishing Log gives a rather liberal definition of where "North Bloodshore" is. I've included a picture of my log and, honestly, it's only half that size. North Bloodshore ends roughly where the yellow fish icon is on the map in the "middle" of the area.
I've framed the North Bloodshore shoreline on two of the smaller maps with my blue player icon.
To help clarify where the southern icon is; it's just slightly north of where the NPC is along the shoreline. I took another picture of me standing next to him for reference. If you stand next to him, you'll get fish from the Costa del Sol region. Need to be a bit further north like I am.
The easiest way to isolate North Bloodshore is to go to the fabulous little hideaway at the very northern corner of the coastline. Great fishing there. Beautiful scenery. Sea Pickles are cute :3