If the bay is 18 feet than they should be there all winter if there is enough of this deep water. Look for any substantial dropoffs that drop into this 18ft water and fish the edge and also up on top of any flats close to this deep water. If there are any weed edges that you can see in the fall, fish along them at first ice (a GPS may be useful).
So if you haven't already, get out there with a depth finder and do some searching in preparation for the hardwater.
If there is any creeks flowing into the bay you could try around them too, especially at first (be careful) and last ice.