Basic evolutionary principle: traits that are selected against do not persist, while those that are selected for tend to spread throughout the population.
Size limits on fish that may be caught and kept has also had an effect on fish size. Fish that grow to be smaller than the size limit reproduce more because the larger fish are all caught.
I want to sign up to aid in the study...
Pay me a small sum of $25.00 an hour and I will fish all day and turn over the records I keep on the fish I catch...
And, apparently, less aggressive bass have an advantage. Must be pretty heavily fished area.