Fecundity is an important demographic parameter that contributes to the productivity of anadromous fish stock dynamics. Yet, studies on fecundity patterns in Pacific salmon (Onchorhynchus spp.) often only include a few years of data, limiting our ability to understand spatio-temporal trends. Here, we used data on 43 hatchery Chinook salmon (O. tshawytscha, Salmonidae) populations in Washington State to evaluate whether average fecundity changed over the past three decades. We then used data from a subset of stocks (18) to evaluate the relationship between fecundity and body length. Our results revealed significant changes in fecundity across the 25-year study period with most stocks showing declines in fecundity over the past decade. Results further showed that Chinook salmon have decreased in length over this same period and that annual variation in mean length explains a majority (62%) of annual variation in mean fecundity. Specifically, we estimated that a 1-mm reduction in length results in 7.8 fewer eggs (95% CI = 6.6–8.9). Given that the majority of Pacific Northwest Chinook salmon in the environment and harvested in fisheries originate from hatchery releases and that nearby hatchery and wild populations generally have similar ocean distributions, these results likely reflect patterns for many populations not included. Combined, our results highlight the need to consider changes in body size and egg production when assessing the dynamics of anadromous fish populations and designing management or conservation plans, particularly for depressed populations.

中文翻译：

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太平洋西北部奇努克鲑鱼的繁殖力趋势

繁殖力是一个重要的人口统计参数，有助于溯河鱼类种群动态的生产力。然而，关于太平洋鲑鱼 ( Onchorhynchus spp.)繁殖力模式的研究通常只包含几年的数据，限制了我们理解时空趋势的能力。在这里，我们使用了 43 个奇努克鲑鱼孵化场的数据 ( O .  tshawytscha, Salmonidae) 华盛顿州的种群来评估平均繁殖力在过去三十年中是否发生了变化。然后，我们使用来自一部分种群 (18) 的数据来评估繁殖力与体长之间的关系。我们的结果显示，在过去 10 年的 25 年研究期间，繁殖力发生了显着变化，大多数股票的繁殖力都出现了下降。结果进一步表明，奇努克鲑鱼的长度在同一时期有所减少，平均长度的年度变化解释了平均繁殖力年度变化的大部分 (62%)。具体而言，我们估计长度减少 1 毫米会导致产卵减少 7.8 个（95% CI = 6.6–8.9）。鉴于环境中和渔业捕捞的大部分太平洋西北奇努克鲑鱼都来自孵化场释放，并且附近的孵化场和野生种群通常具有相似的海洋分布，这些结果可能反映了许多未包括在内的种群的模式。结合起来，我们的结果强调在评估溯河鱼类种群动态和设计管理或保护计划时，需要考虑体型和产卵量的变化，特别是对于低迷种群。