BrianH,
I have an uninvited neighbor that does quite well with a cast net and it seems that the tilapia never learn. Even with his success the tilapia thrived until I finally placed enough cover to limit his casting area. The real damage he di was when he could no longer net the larger fish he started on the fingerlings. That and the introduction of a predator at the same time just about wiped them out.
There must be other control factors, the ponds in my area are stocked with tilapia yet are never over run, in fact barbs usually out number them. Many of these ponds do not have predators. I have seen fingerlings chase fry and I have seen adults eating fry that are feeding on pellets and other surface food.
