Think about cod in the North Atlantic. At any given time, there is a stock of cod, a rate of renewal, and a rate of use—a catch rate. If the rate of renewal exceeds the catch rate, the cod stock grows and cod is being caught sustainably. The cod stock is also being used sustainably if its rate of renewal equals the catch rate and the stock remains constant. But if the catch rate exceeds the rate of renewal, the stock decreases and the cod stock is being used unsustainably.

EYE on the PAST