Ecosystem Overfishing in the Ocean

Fisheries catches represent a net export of mass and energy that can no longer be used by trophic levels higher than those fished. Thus, exploitation implies a depletion of secondary production of higher trophic levels (here the production of mass and energy by herbivores and carnivores in the ecosystem) due to the removal of prey. The depletion of secondary production due to the export of biomass and energy through catches was recently formulated as a proxy for evaluating the ecosystem impacts of fishing�Ci.e., the level of ecosystem overfishing. Here we evaluate the historical and current risk of ecosystem overfishing at a global scale by quantifying the depletion of secondary production using the best available fisheries and ecological data (i.e., catch and primary production). Our results highlight an increasing trend in the number of unsustainable fisheries (i.e., an increase in the risk of ecosystem overfishing) from the 1950s to the 2000s, and illustrate the worldwide geographic expansion of overfishing. These results enable to assess when and where fishing became unsustainable at the ecosystem level. At present, total catch per capita from Large Marine Ecosystems is at least twice the value estimated to ensure fishing at moderate sustainable levels.渔业捕捞可视为一种物质与能量的净输出，此类输出无法再被捕捞层级以上的营养级所利用。因此，捕捞活动会因移除被捕食者，导致更高营养级的次级生产量（即生态系统中植食动物与肉食动物所产生的物质与能量）被消耗殆尽。近年来，学界将捕捞所带来的生物量与能量输出所导致的次级生产量消耗，定义为评估捕捞对生态系统影响的替代指标——也就是生态系统过度捕捞程度。本研究借助当前最优的渔业与生态数据（即捕捞量与初级生产量），量化次级生产量的消耗情况，以此在全球尺度上评估生态系统过度捕捞的历史与当前风险。研究结果显示，1950年代至2000年代期间，不可持续渔业的数量呈上升趋势（即生态系统过度捕捞风险升高），同时也印证了过度捕捞在全球范围内的地理扩张态势。上述结果可用于明确捕捞活动在生态系统层面变得不可持续的时间与地点。当前，大型海洋生态系统（Large Marine Ecosystems）的人均总捕捞量，至少是维持适度可持续捕捞水平的估算值的两倍以上。