Here's another question, that sort of comes from comments that Sam Wright said about salmon. Essentially, what we have left is the most productive parts of the population. The lower production parts have been eliminated by habitat issues, harvest, etc.

Perhaps the same occurs with other resources. When crab, to pick an example at random, live in a generally quality environment with good water movement/exchange and so on they can sustain a (say) 75% exploitation of males >6". On a marginal environment (like 13 and 12) where water exchange is much more limited, etc., those same 6" males can sustain 50%. We seem to like one size fits all management paradigms.