Juvenile Salmon Usage of the Skeena River Estuary

Migratory salmon transit estuary habitats on their way out to the ocean but this phase of their life cycle is more poorly understood than other phases. The estuaries of large river systems in particular may support many populations and several species of salmon that originate from throughout the upstream river. The Skeena River of British Columbia, Canada, is a large river system with high salmon population- and species-level diversity. The estuary of the Skeena River is under pressure from industrial development, with two gas liquefaction terminals and a potash loading facility in various stages of environmental review processes, providing motivation for understanding the usage of the estuary by juvenile salmon. We conducted a juvenile salmonid sampling program throughout the Skeena River estuary in 2007 and 2013 to investigate the spatial and temporal distribution of different species and populations of salmon. We captured six species of juvenile anadromous salmonids throughout the estuary in both years, and found that areas proposed for development support some of the highest abundances of some species of salmon. Specifically, the highest abundances of sockeye (both years), Chinook in 2007, and coho salmon in 2013 were captured in areas proposed for development. For example, juvenile sockeye salmon were 2–8 times more abundant in the proposed development areas. Genetic stock assignment demonstrated that the Chinook salmon and most of the sockeye salmon that were captured originated from throughout the Skeena watershed, while some sockeye salmon came from the Nass, Stikine, Southeast Alaska, and coastal systems on the northern and central coasts of British Columbia. These fish support extensive commercial, recreational, and First Nations fisheries throughout the Skeena River and beyond. Our results demonstrate that estuary habitats integrate species and population diversity of salmon, and that if proposed development negatively affects the salmon populations that use the estuary, then numerous fisheries would also be negatively affected.

洄游性鲑鱼在向海洋迁徙的途中会途经河口栖息地，但相较于其生命周期的其他阶段，学界对这一阶段的了解仍相对匮乏。大型河系的河口栖息地尤其可为源自全上游流域的多种鲑鱼种群及物种提供栖息支持。加拿大不列颠哥伦比亚省的斯基纳河（Skeena River）便是这样一处大型河系，其鲑鱼种群与物种多样性水平极高。该河河口正面临工业开发带来的压力：两座天然气液化终端与一处钾肥装卸设施正处于不同阶段的环境审查流程中，这也推动了学界针对幼鲑在该河口栖息利用情况的研究。本研究于2007年与2013年在斯基纳河河口全域开展了幼鲑科鱼类采样项目，以探究不同鲑鱼物种与种群的时空分布格局。两年间，研究团队在该河口全域共捕获6种溯河洄游幼鲑科鱼类，且发现拟建开发区域内部分鲑鱼物种的种群丰度位居该区域前列。具体而言，两年间的红大马哈鱼（sockeye）、2007年的奇努克鲑（Chinook）以及2013年的银大马哈鱼（coho）的最高丰度样本均捕获于拟建开发区域内。举例来说，拟建开发区域内的幼红大马哈鱼丰度可达其他区域的2至8倍。遗传种群溯源分析显示，本次捕获的奇努克鲑与绝大多数红大马哈鱼均源自斯基纳河流域全境，而部分红大马哈鱼则来自纳斯河、斯蒂克因河、阿拉斯加东南部以及不列颠哥伦比亚省北中部沿海的沿岸水系。这些鲑鱼资源支撑了斯基纳河流域及更广范围内的大规模商业渔业、休闲渔业以及原住民第一民族（First Nations）渔业。本研究结果表明，河口栖息地整合了鲑鱼的物种与种群多样性；若拟建开发活动对依赖该河口的鲑鱼种群造成负面影响，则众多相关渔业也将随之受损。