There 's no "winter" Matt, in the warm regions of the country tilapia spawn 3-4 times a year, in the "cold" regions tilapia spawn twice a year so all year long there 's a supply of bite size tilapia for the bass to eat, they don 't need the trout.
The situation with commercial fishermen is that of absolute ignorance, heck, most of them barely finished elementary school, so many of them view bass as a fish that eats the fish they fish for and don 't like bass, they want to see it dead and gone; but as I said, they are ignorant, the reason why they have good tilapia fishing is because bass are there eating away the excess tilapia population that the same tilapia produce. They don 't know that in an environment where there 's only tilapia it grows stunted. Tilapia has intersting breeding habits, first of all it 's a mouthbreeder, secondly, it 's very sexually active and most importantly it matures sexually at a very young age, at 6 months of age it 's ready to breed so if there 's nothing there to control their population the population reaches critical numbers in a very short period of time, they eat away every vegetable matter they can chew upon and when that 's gone they become detritophagous ( mud eaters ), since the population is too large and there 's not enough food they can 't grow, they stunt but still are sexually mature so they spawn which adds more numbers to the population, a never ending vicious circle. But stunted fish are not good enough for human consumption because they are too small and they don 't have the minimum legal size ( 10 inches ) they can 't be kept by the fishermen.
Actually what most of us know as tilapia is not really tilapia from the genus tilapia, we have got used to call tilapia to almost every fish that looks like tilapia when it 's actually a different species belonging to the genus Orechromis which is waht the mexican government stocks in these three principal species: O. aureus, O. mossambicus and O. niloticus, plus a few hybrids of those three species.
So for us who fish in Mexico we have this situation where unless it 's woody cover or some plant the tilapia won 't eat like water hyacinth the lakes are weedless, if you want to catch fish here where "tilapia" is present you have to be good as fishing structure beacuse that where you 'll find the fish.