As far as I know, the circles only represent waypoints. Along this 'route' the minefield will be laid down.
I don't know if there's a map that displays all the minefields for sh3, but if you want to check for other minefields, open up the MissionEditor (it's in the same folder as your sh3.exe).
In the top of the screen, select the start and end date of the period you wish to see.
Then, click the little 'open folder' icon, and open 'campaign_scr.mis'.
Now if you click the little hand-icon, you can move around on the map. On the map, that icon made of two triangles (like in the screenshot just above Helgoland) indicates a minefield. If you don't have the little hand icon active, you can select these minefield icons. And after selecting one of them, right-click and select 'properties'. There you can see (among others) the date the minefield will appear in game, and the date when it will be gone again.
By the way, I played five careers out of Wilhelmshaven before I read about this minefield. (Someone had the same problem as you) So I guess I was just very very lucky
