Although most fisheries assessment and management focuses on the status of individual stocks, and regulations are commonly established as single-species total allowable catch limits (TACs), much of the catch from global fisheries comes from mixed-stock fisheries where species cannot be harvested separately. We show that in some fisheries where TAC and catch of demersal fish stocks are tracked, the average fraction of TAC harvested ranges from 21% to 68% overall and is declining. This is, in part, related to efforts to protect all species from overfishing, leading to ‘choke species’, which limit fishing pressure on other target species. While some choke species arise from a mix of low and high-productivity species, others result from allocation processes, which can be aggravated by shifting distributions due to climate change. Underutilization of TACs can also result from market limitations, low value of individual species, undercapacity or management measures. Proposed methods for increasing long-term yield require species to be managed in stock groups, or allowing the abundance of some stocks to fall below target reference points. We suggest that the observed low and declining aggregate harvests are due, primarily, to the focus on single-stock sustainability measures, rather than performance of the fisheries in relation to potential overall yield. While there is a growing consensus that single-species management should be replaced by an ecosystem-based approach, this will require clear legislative directives regarding management of the trade-offs involved. Time series considered in this analysis do not extend beyond 2019.

中文翻译：

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混合渔业中的配额使用

尽管大多数渔业评估和管理侧重于单个种群的状况，并且法规通常制定为单一物种总允许捕捞限量（TAC），但全球渔业的大部分渔获量来自混合种群渔业，其中物种无法单独捕捞。我们发现，在一些追踪 TAC 和底栖鱼类种群捕获量的渔业中，总体 TAC 捕获量的平均比例为 21% 至 68%，并且正在下降。这在一定程度上与保护所有物种免遭过度捕捞的努力有关，过度捕捞导致“物种窒息”，从而限制了对其他目标物种的捕捞压力。虽然一些窒息物种是由低生产力和高生产力物种混合产生的，但其他物种则是由分配过程造成的，而气候变化导致的分配变化可能会加剧这种情况。 TAC 的利用不足也可能是由于市场限制、个别物种价值低、能力不足或管理措施造成的。提高长期产量的拟议方法要求对种群进行种群管理，或者允许某些种群的丰度低于目标参考点。我们认为，观察到的总产量较低且不断下降的主要原因是对单一种群可持续性措施的关注，而不是与潜在总产量相关的渔业表现。尽管越来越多的人认为单一物种管理应该被基于生态系统的方法所取代，但这需要就所涉及的权衡管理制定明确的立法指令。本分析中考虑的时间序列不超过 2019 年。