Just to be correct ...It is not that they dont get as far south as Katherine, as they are certainly further south but more that there isnt enough suitable waterways there for them. for example there is a large swamp down on the roper river that has thousands of them.. and they occur as far south as central NSW, from what I have seen.

I dont really know much about the public land hunting around Darwin. Marrakai and Co are the guys who get right into it...