That matters because theory suggests that the maximum sustainable yield that can be cropped from fishery comes when the biomass of a target species is about 50% of its original levels.

• 这点之所以很重要是因为理论指出，一个渔场若能够获得最高持续产量，只有当目标物种的生物量是原来水平的50%25时才能实现。