The key to sustainability is a systems capacity to recover after a disturbance, not the ability to hold it in a notional optimal state. Complex systems are constantly moving through adaptive cycles of rapid growth, conservation, release and reorganisation. You can’t ‘hold’ it in one condition of ‘optimal sustainable yield’ because the system continually self organises. The myth of the optimal state stems from our mistaken belief that we are in control and the systems we are managing are simple systems.