Although I have never been to Tasmania and not familiar with the terrain around the named area, I do have a number of years experience handling cattle. Would it be possible for the council rangers or whoever is trying to control these cattle, to build portable yards in the forest areas where these animals are known to roam? It would take not just the yards but also lead up races so the cattle could be enticed into the yards with feed and watering points, you would also need staff to be there watching so that as they go past each point of the raceway’s gates can be shut behind them. This is a suggestion based on what I have done in earlier lifetime when dealing with livestock that have come down from station areas. The cattle can then be loaded onto trucks and taken to a abattoir to be processed for either human or pet food consumption. Yes, it would be time consuming to get them all but worth it in the long run.