Manchester Research Laboratory, Northwest Fisheries Science Center, National Oceanic and Atmospheric Administration Fisheries, Manchester, Washington, United States of America.
PLoS One. 2013 Sep 5;8(9):e73427. doi: 10.1371/journal.pone.0073427. eCollection 2013.
Habitat modifications resulting from human transportation and power-generation infrastructure (e.g., roads, dams, bridges) can impede movement and alter natural migration patterns of aquatic animal populations, which may negatively affect survival and population viability. Full or partial barriers are especially problematic for migratory species whose life histories hinge on habitat connectivity.
METHODOLOGY/PRINCIPAL FINDINGS: The Hood Canal Bridge, a floating structure spanning the northern outlet of Hood Canal in Puget Sound, Washington, extends 3.6 meters underwater and forms a partial barrier for steelhead migrating from Hood Canal to the Pacific Ocean. We used acoustic telemetry to monitor migration behavior and mortality of steelhead smolts passing four receiver arrays and several single receivers within the Hood Canal, Puget Sound, and Strait of Juan de Fuca. Twenty-seven mortality events were detected within the vicinity of the Hood Canal Bridge, while only one mortality was recorded on the other 325 receivers deployed throughout the study area. Migrating steelhead smolts were detected at the Hood Canal Bridge array with greater frequency, on more receivers, and for longer durations than smolts migrating past three comparably configured arrays. Longer migration times and paths are likely to result in a higher density of smolts near the bridge in relation to other sites along the migration route, possibly inducing an aggregative predator response to steelhead smolts.
CONCLUSIONS/SIGNIFICANCE: This study provides strong evidence of substantial migration interference and increased mortality risk associated with the Hood Canal Bridge, and may partially explain low early marine survival rates observed in Hood Canal steelhead populations. Understanding where habitat modifications indirectly increase predation pressures on threatened populations helps inform potential approaches to mitigation.
人类交通和发电基础设施（如道路、水坝、桥梁）导致的栖息地改变会阻碍水生动物种群的移动，并改变其自然迁徙模式，这可能对其生存和种群生存力产生负面影响。对于那些其生命史取决于栖息地连通性的洄游物种来说，完全或部分的障碍物尤其成问题。
方法/主要发现：胡德运河大桥是一座横跨华盛顿州普吉特湾胡德运河北出口的浮桥，水下延伸 3.6 米，形成了胡德运河到太平洋洄游的钢头鱼的部分障碍。我们使用声学遥测技术监测通过胡德运河、普吉特湾和胡安·德富卡海峡的四个接收器组和几个单个接收器的钢头鱼幼鱼的迁移行为和死亡率。在胡德运河大桥附近检测到 27 个死亡事件，而在整个研究区域部署的 325 个接收器中，只有一个死亡记录。在胡德运河大桥的接收器组中，钢头鱼幼鱼的检测频率更高，在更多的接收器上，持续时间更长，而在三个类似配置的接收器组中，钢头鱼幼鱼的检测频率更低。更长的迁移时间和路径可能导致在大桥附近的幼鱼密度更高，与迁移路线上的其他地点相比，这可能会引起对钢头鱼幼鱼的聚集性捕食者反应。
结论/意义：本研究提供了强有力的证据，证明胡德运河大桥对洄游产生了实质性的干扰，并增加了死亡率风险，这可能部分解释了胡德运河钢头鱼种群早期海洋存活率低的原因。了解栖息地改变如何间接增加受威胁种群的捕食压力，有助于为缓解措施提供信息。
