Dr Carl O'Brien:
Partly because it is a question of input and output. To a certain extent you can control fisheries exploitation—the harvest rate. You can control how many boats go to sea and, by implication, how many fish are taken out of the sea. The biomass is a consequence of your management being appropriate or right for the sea and for the species. If you get the balance between exploitation or harvest rate correct, your biomass should continue to grow. One is input; one is output.