Selective harvest increasing populations is a very difficult arguement to make. It really matters more on spawning pressure than anything else. Leaving the biggest fish as spawners is great but older fish often have the same fertility issues other animals and humans have. Also larger fish have larger appetities and as soon as the wigglers enter the water column those post spawn adults are on a major feeding binge. Many times fish parents will guard the fry after they are free swimming. I have caught bass in a small local stream that were clearly guarding swarms of small fry, released them 20 ft away and they immediately went back to guarding. Mothers seldom eat their own spawn but the neighbor…different story Taking them after spawn removes what little protection the fry have. Leaving too many large adults in a small body of water creates over crowding and many won’t even get a chance to spawn. I have raised tropicals in a 100 aquarium hatchery for 30 years as well as fished large and small bodies of water for 30 years. I could argue this either way from now to dooms day. One marvelous aspect of fishing culture is that they have an incredible ability to bounce back…again providing certain criteria are met. When lets say crappie populations drop for what ever reason (except food base depletion) they have an incredible opportunity to rebound in 2-5 years based on lack of predation. I believe that carp populations have much much more to do with loss than human predation. Carp will raid nests and consume thousands of fry long before they ever get a chance. Fry and juvenile fish have plenty of food base in almost any water. Once they reach 1 1/2″ or so and require larger size and more volumn food the story changes. The single biggest thing you can do to increse populations is increase cover. Sink as many Christmas trees as possible. I like to leave a line attached so when the green has rotted away they can be removed in small ponds. In bigger water don’t worry. There are many kinds of crustaceons that feed on that decaying matter that feed the entire chain. Now another interesting twist. Years ago I fished Kentucky Lake with a local guide and six other members of our party. Every one of us (8) were using the exact same flourescent green jig and 5# mono. Four other members were in his boat and we were 10 feet away. Everyone was casting within a 20ft circle. The guide caught over 30 monster slabs and I caught 5-6 and noone else caught anything. The guys in his boat even had him tie their jigs on believing he must have some attractant on his hands. No use. Now you would have had 6 men who, if fishing by themselves, would have sworn there were no fish in that lake. I could have thought there were some but hard to catch. The guide nailed fish after fish after fish. It was becuase the bite was extremely light and you really had to focus.