Forrest was just a casualty of the extreme depth the Tigers have on the back-end. It leaves 9 WHL rearguards on the roster.
This move pairs the Tigers roster down to 24 players. (25 including Rathjen) which is under the league limit of 25. I guess the Tigers don't have to make a move, but surely 9 Dman is still 1-2 too many.