I would suggest that the CWD are able to live in much larger groups and at a higher density than the more territorial muntjac, thats why they spread less. I have personally filmed fifty cwd in one field. And yet five miles away there's none. They're two different deer in many regards, living completely opposite lives.A sigificant reason is that water deer suffer badly from post capture myopathy and often don't survive being transported. Muntjac are far more robust and easier to move around for (illegal) introductions

