The spatial and temporal distribution of spawning activity by autumn‐run Chinook salmon Oncorhynchus tshawytscha (Walbaum) was examined across multiple years. The study period included two years of extreme drought conditions when water temperatures in the spawning reach of the Stanislaus River were considered sub‐optimal for spawning and egg incubation. Despite varying levels of superimposition, redd counts and densities remained stable and positively associated with river location, indicating that superimposition may be driven by habitat preference rather than the absence of suitable spawning locations. Spawning occurred slightly later during drought years (6–10 days later compared with wetter years). This delay was attributable to deferred migration instead of deferred spawning, and the majority of redds were constructed at water temperatures exceeding the optimal temperature range. As a consequence, estimates of juvenile production during 2014 and 2015 were among the lowest on record. These findings may be related in part to the high hatchery contribution to the population, above‐average temperatures during spawning and incubation, and superimposition rates. Management recommendations include adequate cold‐water storage in the upstream reservoir, refined spawning habitat restoration techniques in the light of superimposition rates and, on a broader system scale, actions that reduce the amount of stray hatchery Chinook salmon.

中文翻译：

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在不同环境条件和丰度的六年中，奇努克鲑鱼的繁殖时间和栖息地使用的稳定性

对秋游奇努克鲑 Oncorhynchus tshawytscha (Walbaum) 产卵活动的时空分布进行了多年研究。研究期间包括两年的极端干旱条件，当时斯坦尼斯劳斯河产卵区的水温被认为不适合产卵和卵孵化。尽管叠加水平不同，redd 计数和密度保持稳定并与河流位置呈正相关，表明叠加可能是由栖息地偏好而不是缺乏合适的产卵地点驱动的。在干旱年份产卵发生得稍晚（与多雨年份相比，延迟 6-10 天）。这种延迟是由于延迟迁移而不是延迟产卵，大多数redds是在超过最佳温度范围的水温下建造的。因此，对 2014 年和 2015 年幼鱼产量的估计是有记录以来最低的。这些发现可能部分与孵化场对种群的高贡献、产卵和孵化期间高于平均水平的温度以及叠加率有关。管理建议包括在上游水库中储存足够的冷水，根据叠加率改进产卵栖息地恢复技术，以及在更广泛的系统范围内减少流浪孵化场奇努克鲑鱼数量的行动。这些发现可能部分与孵化场对种群的高贡献、产卵和孵化期间高于平均水平的温度以及叠加率有关。管理建议包括在上游水库中储存足够的冷水，根据叠加率改进产卵栖息地恢复技术，以及在更广泛的系统范围内减少流浪孵化场奇努克鲑鱼数量的行动。这些发现可能部分与孵化场对种群的高贡献、产卵和孵化期间高于平均水平的温度以及叠加率有关。管理建议包括在上游水库中储存足够的冷水，根据叠加率改进产卵栖息地恢复技术，以及在更广泛的系统范围内减少流浪孵化场奇努克鲑鱼数量的行动。