I am not a scholar in this area, but I've carried knives for 65 years or more. In my working life it was not unusual for me to have four or more on me,
depending on the project and my various functions therein. As I have seen the term gralloching knife, it has usually applied to deer hunting, and having
never field dressed a deer, am unfamiliar with the size. As it was not legal (in my understanding) for the average guy to take a deer, he'd not need such.
He would, however, want a small blade to scale and gut fish and/or rabbits and other small game. Thus the sgian dhu. Maybe? I certainly would
never have thought of using something the size of a dirk or sgian achlais for fish; my pocket knife, or my mother's paring knives if I brought the string
back home before cleaning.