Columbia River hatcheries release millions of juvenile Chinook Salmon Oncorhynchus tshawytscha to support fisheries and mitigate for historical productivity declines from dam construction and upriver habitat losses. Recent federal biological opinions for Federal Columbia River Power System operations also have mandated restoration of estuarine rearing habitats to mitigate for mortality of naturally produced (NP) salmon at main-stem dams. We compared genetic stock compositions, distributions, abundances, and length frequencies of hatchery-marked and unmarked Chinook Salmon to evaluate the extent of hatchery influence on nearshore estuarine habitat use and the potential for interactions between hatchery-origin (HO) and NP salmon. Cumulative Chinook Salmon releases from all hatcheries in 2010 and 2011 dictated estuarine stock composition, abundance, and life histories during the spring–summer migration peak. Naturally produced salmon from the lower Columbia River populations, including many fry migrants, were most abundant, but larger HO juveniles also frequented nearshore sites, where their total biomass often equaled or exceeded that of NP fish. Large releases of a single stock of origin (Spring Creek Group fall run) in April and May created sharp pulses in the estuary entry timing of fingerling-sized salmon and dominated abundance and stock composition at some sites. Successive releases from scores of hatcheries during spring and early summer ensured a consistent presence of HO salmon near shore, regardless of the habitat-specific residence times of individual fish. Overall, the historical replacement of diverse wild populations with fewer hatchery stocks of a narrow size range and migration timing has intensified nearshore habitat use during the spring–summer migration peak and reduced life history variation of Columbia River Chinook Salmon. Such changes could undermine the fish conservation goals of both hatchery mitigation and estuary restoration programs.

中文翻译：

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哥伦比亚河口近岸栖息地孵化场和自然生产的奇努克鲑鱼的丰度和分布

哥伦比亚河孵化场释放了数百万条奇努克鲑鱼Oncorhynchus tshawytscha幼鱼支持渔业并缓解因大坝建设和上游栖息地丧失而导致的历史生产力下降。最近针对联邦哥伦比亚河电力系统运营的联邦生物学意见还要求恢复河口养殖栖息地，以降低主干坝上自然产生的 (NP) 鲑鱼的死亡率。我们比较了孵化场标记和未标记的奇努克鲑鱼的遗传种群组成、分布、丰度和长度频率，以评估孵化场对近岸河口栖息地利用的影响程度以及孵化场原产地 (H2O) 和 NP 鲑鱼之间相互作用的潜力。2010 年和 2011 年所有孵化场的累积奇努克鲑鱼释放决定了春夏洄游高峰期间河口种群的组成、丰度和生活史。来自哥伦比亚河下游种群的自然产生的鲑鱼，包括许多鱼苗移民，数量最多，但较大的 HO 幼鱼也经常光顾近岸地点，它们的总生物量通常等于或超过 NP 鱼的总生物量。4 月和 5 月大量释放单一来源种群（Spring Creek Group 秋季运行）在鱼种大小的鲑鱼进入河口的时间产生了尖锐的脉冲，并主导了某些地点的丰度和种群组成。春季和初夏期间从数十个孵化场连续放流确保了近岸 HO 鲑鱼的持续存在，无论个体鱼类的栖息地特定停留时间如何。总体，不同野生种群的历史更替与较小规模范围和迁移时间的孵化场种群数量减少，在春夏季迁移高峰期间加强了近岸栖息地的利用，并减少了哥伦比亚河奇努克鲑鱼的生活史变化。这种变化可能会破坏孵化场缓解和河口恢复计划的鱼类保护目标。