Changes in population demographic structure can have tangible but unknown effects on management effectiveness. Fishery management of Pacific salmon is often informed by estimates of the number of spawners expected to produce maximum sustainable yield (SMSY), implicitly assuming that reproductive output per spawner does not change over time. However, many salmon populations have experienced long‐term trends in age, sex and length compositions that have resulted in smaller body sizes of mature fish. We present an empirically based simulation approach for evaluating management implications of declining reproductive output resulting from shifting demographics. We simulated populations with or without demographic trends, selective or unselective harvests, and harvest policies based on assessment methods that did or did not account explicitly for demographic trends when estimating SMSY. A management strategy evaluation showed reduced expected harvests and run sizes when populations exhibited negative demographic trends. Reduced abundances and increased conservation risks (higher probability of falling below an abundance threshold) could be partially mitigated by using stock‐recruitment analyses based on total egg mass instead of spawner abundance, or via precautionary management where target escapements were higher than SMSY, especially in fisheries that selectively removed large fish. Explicit accounting of demographic trends in stock‐recruit analyses resulted in up to 25% higher run sizes and up to 20% lower conservation risks compared to traditional methods when trends toward smaller, younger and male‐biased runs were present in the population. Conservation of population demographic structure may be critical for sustaining productive fish populations and their benefits to ecosystems and people.

中文翻译：

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在渔业管理中考虑鲑鱼体型下降可以降低保护风险


人口结构的变化可能对管理有效性产生有形但未知的影响。太平洋鲑鱼的渔业管理通常以预期产生最大可持续产量 （SMSY） 的产卵器数量估计为依据，隐含地假设每个产卵器的繁殖产量不会随时间变化。然而，许多鲑鱼种群在年龄、性别和长度组成方面经历了长期趋势，这导致成熟鱼的体型变小。我们提出了一种基于实证的模拟方法，用于评估人口结构变化导致生殖产出下降的管理影响。我们模拟了有或没有人口趋势的种群、选择性或非选择性收获，以及基于评估方法的收获政策，这些评估方法在估计 SMSY 时明确考虑了或没有明确考虑人口趋势。管理策略评估显示，当种群表现出负面的人口趋势时，预期收成和运行规模会降低。通过使用基于总卵质量而不是产卵器丰度的种群补充分析，或通过目标擒纵机构高于 SMSY 的预防性管理，可以部分减轻丰度降低和保护风险（低于丰度阈值的可能性更高），特别是在选择性移除大鱼的渔业中。当种群中存在较小、年轻和偏向男性的趋势时，与传统方法相比，在种群招募分析中明确考虑人口趋势导致运行规模增加多达 25%，保护风险降低多达 20%。 保护种群人口结构对于维持生产性鱼类种群及其对生态系统和人类的益处可能至关重要。