Hatchery production of Pacific salmon for release into the environment is a common tool for conservation and supplementation of depleted stocks. Hatchery conditions are controlled to support high survival rates; however, once released into the environment, managers have little control over conditions experienced by juveniles. Thus, release timing is a critical decision in hatchery operations. This 3-year study used acoustic telemetry to estimate release timing effects on migration survival of fall run Chinook Salmon from the largest hatchery in California: the Coleman National Fish Hatchery. Juvenile Chinook Salmon implanted with JSATS transmitters were released in two or more groups each year, concomitant with the regular hatchery production. Arrays of acoustic monitors were deployed at six locations within the 517 km migration route to estimate reach-specific survival of each release. Mark-recapture models identified both year and release timing effects on reach-specific survival. In years when release effects were well-supported, survival was higher in the earlier release group. Survival in subsequent releases was similar or significantly lower indicating that conditions in the river may decline or stay the same but improvement was not observed. Survival was consistently high in the first 92 km of the migration route and may be related to predator swamping from the release of millions of hatchery fish. Survival declined, and became more variable, within the lower 425 km of the river with the lowest rates observed in the tidal bay-delta. These results indicate that both year and release timing can strongly influence survival and that time between releases likely influences the magnitude of the effect.

中文翻译：

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释放时间对科尔曼国家鱼类孵化场秋游奇努克鲑鱼幼鱼表观存活率的影响

用于释放到环境中的太平洋鲑鱼孵化场是保护和补充枯竭种群的常用工具。孵化场条件得到控制以支持高成活率；然而，一旦被释放到环境中，管理人员几乎无法控制青少年所经历的状况。因此，释放时间是孵化场操作中的关键决定。这项为期 3 年的研究使用声学遥测技术来估计释放时间对加利福尼亚最大孵化场：科尔曼国家鱼类孵化场秋游奇努克鲑鱼洄游存活率的影响。植入了 JSATS 发射器的幼年奇努克鲑鱼每年分两组或更多组放生，同时进行常规孵化场生产。在 517 公里迁移路线内的六个位置部署了声学监测器阵列，以估计每次释放的到达特定存活率。标记重新捕获模型确定了年份和发布时间对到达特定生存率的影响。在释放效应得到充分支持的年份，早期释放组的存活率更高。随后释放的存活率相似或显着降低，表明河流状况可能下降或保持不变，但未观察到改善。在洄游路线的前 92 公里处，存活率一直很高，这可能与数百万孵化鱼放生导致捕食者沼泽有关。在潮汐湾三角洲观察到的最低速率的河流下游 425 公里内，生存率下降，并且变得更加多变。