The best answer I can give can only be applied to small lakes. When I first started with MDC we did a project at Jamesport Community Lake. For some reason it always provided good crappie fishing while almost every other small lake had stunted crappie. Through a tagging study we found that that 80-85% of the crappie over 8 inches were harvested every year! This kept them from stunting in the smaller lake. In a large reservoir like Truman, I'd be very surprised if 40% were harvested every year. But this is one of those questions that's makes my job challenging. Managing a resource you can't walk out and look at or count is difficult sometimes. Crappie only live about 5 years if they are growing good. An 8 year old crappie is ancient. They are a short-lived species and can handle a pretty good harvest rate. Length limits protect smaller fish so they can grow to desired size and help offset lost year classes when the spawn isnt very successful. Reduced daily limits (15 vs 30) help spread the harvest to more anglers. Getting an actual number of crappie in a lake of any size is an extremely difficult task. Getting an estimate in a lake the size of Truman is virtually impossible. The only way to estimate it would be to set nets to cut off small coves and kill every fish in the cove. Even then the estimate is questionable. Many other states used this method in the past but virtually none do so anymore. I've not heard of MDC doing it during my 26 years.