Is episodic river acidification affecting wild Atlantic salmon populations in the Maritimes?

大西洋鲑鱼是加拿大东部人民的标志性物种，具有重要的经济、文化、人类生存和生态价值。近几十年来，返回加拿大河流的大西洋鲑鱼数量已降至前所未有的低点（历史水平的20%）。尽管作出了巨大的恢复和保护努力，但由于海上鱼类死亡率高仍然是一个令人困惑的问题，我们未能阻止鱼类数量的下降。最近的研究提出了这样一种可能性，即春季融雪期间的偶发性河流酸化可能是问题的一个重要而被忽视的部分。这一自然过程因人类活动（如燃煤）产生的酸沉淀而加剧，已知会通过增加河流中铝的生物利用度来影响鲑鱼。在酸性条件下（pH <6），这种天然丰富的金属溶解成无机形式（Ali），即使在短期，低水平的暴露中也会损害鲑鱼的鳃。一个特别令人关注的影响是银化，海水适应的一个重要的生理过程，发生在春季迁出（小鲑鱼）阶段的损害。最近欧洲和美国的研究提供的证据表明，小鲑鱼在淡水中的酸度/阿里的间歇性暴露可以减少早期海洋生存的20%至50%，在剂量依赖性的问题。尽管可能发生，但尚未在加拿大大西洋地区调查该问题。例如，Miramichi河（NB）拥有世界上最大的鲑鱼群，其pH值在春季经常降至6以下。我们的项目旨在回答以下问题：是否间歇性河流酸化显着有助于在加拿大东部鲑鱼的低回报率？在四年的时间里，我们将从各种NB和NS河流收集水样和迁移的小鲑鱼。我们将特别测量水样中的pH值和阿里浓度，铝生物累积和鱼鳃中的银化生物标志物，以及小鲑鱼的盐度耐受性。该项目旨在通过实施有效的缓解策略（如石灰），为影响大西洋鲑鱼种群的可采取行动的淡水因素的管理决策提供信息。

The Atlantic salmon is an iconic species for the people of Eastern Canada, with important economic, cultural, human subsistence and ecological values. In recent decades, the number of Atlantic Salmon returning to Canadian rivers has declined to unprecedented lows (20% of their historic levels). Despite great restoration and conservation efforts, we have failed to prevent the declines as high fish mortality at sea remains a puzzling issue. Recent studies have raised the possibility that episodic river acidification during spring snowmelt may be an important and overlooked part of the problem. This natural process, which has been exacerbated by acid precipitation from human activities (e.g. coal burning), is known to affect salmonids by increasing aluminum bioavailability in rivers. Under acidic conditions (pH <6), this naturally abundant metal is solubilized into inorganic forms (Ali) that can damage salmonids gills, even in short-term, low-level exposures. A particularly concerning effect is the impairment of smoltification, a critical physiological process for seawater adaptation, occurring during the spring outmigration (smolt) phase. Recent European and American studies have provided evidence that episodic exposure of smolts to acidity/Ali in freshwater can reduce early ocean survival by 20 to 50%, in a dose-dependent matter. This issue has not yet been investigated in Atlantic Canada, despite its potential occurrence. For example, the Miramichi river (NB), which has the largest salmon runs in the world, has a pH that often drops below 6 in the spring. Our project aims at answering the following question: Does episodic river acidification significantly contribute to the low return rates of salmons in Eastern Canada? For four years, we will collect water samples and migrating smolts from various NB and NS rivers. We will notably measure pH and Ali concentrations in water samples, Al bioaccumulation and smoltification biomarkers in fish gills, as well as smolt salinity tolerance.The project is designed to inform management decisions on actionable freshwater factors affecting Atlantic salmon populations, by implementing effective mitigation strategies if applicable (e.g. liming).