Science Daily reported today on findings from scientists at the University of Toronto that show traditional fishing policies related to "keepers" may be mis-guided. Their research found that having fishermen keep small fish, and throw the big ones back, would result in more sustainable fisheries. This is the opposite of the situation in most fisheries today, in which "keepers" are only those fish above a certain size.
Their findings make sense. The bigger fish in a population are those most likely to be mature and able to reproduce, thus producing more fish and larger fish stocks.