Distributing fishing mortality across the widest possible range of species, stocks, and sizes in proportion to their natural productivity (i.e., balanced harvest, BH) has been suggested as a new paradigm of fisheries management to minimize the effects of fishing on the ecosystem structure while maximizing overall yield. Models that have been used to test the effects of BH, however, usually concentrate on fish and assume full alignment of fishing mortality with the productivity of each species. Here, we used the trophic-level-based approach EcoTroph to investigate the effects of BH on the biomass and catch trophic spectra of a virtual ecosystem assuming (1) a full implementation, where all trophic levels can be fished according to their productivity and (2) a more realistic implementation, where low and intermediate trophic levels are only partially exploitable by fisheries mimicking current technological and practical limitations. EcoTroph simulations show that a BH fishing pattern does not fully maintain ecosystem structure but results in small structural changes and a large total yield. The resulting catch, however, was dominated by low trophic levels (i.e., 2–2.5). Considering that fishing mortality cannot be fully aligned to all species, we observed an additional adverse impact of BH: the increase in unexploitable biomass. In contrast, protecting lower trophic levels appeared as an efficient way to limit the impact of fisheries on the highest trophic levels, which play a crucial role in ecosystem stability and biodiversity. We conclude that given our inability to align fishing mortality to the productivity of each species, BH could lead to strong adverse impacts on the ecosystem. Instead of expanding fishing pressure toward new species and trophic levels, we first should ensure the sustainable management of those that are currently harvested beyond their capacity to replenish.

中文翻译：

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钓鱼无踪？使用 EcoTroph 评估平衡收获方法

根据自然生产力（即平衡收获，BH）在尽可能广泛的物种、种群和规模范围内分配捕捞死亡率已被建议作为渔业管理的新范式，以尽量减少捕捞对生态系统结构的影响，同时使总产量最大化。然而，用于测试 BH 影响的模型通常侧重于鱼类，并假设捕捞死亡率与每个物种的生产力完全一致。在这里，我们使用基于营养级的方法 EcoTroph 来研究 BH 对虚拟生态系统的生物量和捕获营养谱的影响，假设 (1) 完全实施，其中所有营养级都可以根据其生产力和 ( 2）更现实的实现，模仿当前技术和实际限制的渔业只能部分利用中低营养水平。EcoTroph 模拟表明，BH 捕鱼模式不能完全维持生态系统结构，但会导致结构变化小，总产量大。然而，由此产生的渔获量主要是低营养水平（即 2-2.5）。考虑到捕捞死亡率无法与所有物种完全一致，我们观察到 BH 的额外不利影响：不可利用的生物量增加。相比之下，保护低营养级似乎是限制渔业对最高营养级影响的有效方法，后者在生态系统稳定性和生物多样性方面发挥着至关重要的作用。我们得出的结论是，鉴于我们无法将捕捞死亡率与每个物种的生产力联系起来，BH 可能对生态系统产生强烈的不利影响。与其将捕捞压力扩大到新物种和营养水平，我们首先应该确保对目前捕捞量超出其补充能力的那些鱼进行可持续管理。