Diadromous fishes migrate between marine and fresh waters for reproduction. For anadromous species, which spawn in freshwater, improved access to freshwater spawning and nursery habitats and ability of juveniles to emigrate to the ocean may support population recovery. Despite the potentially enormous influence of early life stage survival on adult population size, managers and scientists have limited capacity to assess numbers of juvenile anadromous fishes leaving freshwater ecosystems. Such data are critical for evaluating reproductive success and habitat suitability and have been identified as a top priority in anadromous fish research and management. We developed a state‐of‐the‐art underwater video and computational system to collect videos to estimate abundances and migration timing for juvenile river herring (Alosa pseudoharengus; Alosa aestivalis). We collected continuous video in the Monument River (Bourne, Massachusetts, USA) from June to November 2017. We trained three types of neural network models to detect and count fish in video frames and evaluated model performance by comparing human counts to model outputs. Our top model assessed presence and absence (F1 = 87%) and counted fish (counting error 9.4%) with an accuracy comparable to human counters (F1 = 88%). Our system's capability to collect accurate counts of emigrating juveniles will provide critical information that could be related to the numbers of spawning adults, system‐specific productivity, and spawning and nursery habitat suitability. Both the video collection system and computational model may be transferrable to other sites and for other species where tracking juvenile emigration may inform management efforts.

中文翻译：

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用于估算河流系统中洄游幼鱼丰度的视频监测和计算系统

产卵鱼类在海水和淡水之间洄游进行繁殖。对于在淡水中产卵的溯河产卵物种来说，改善淡水产卵和育苗栖息地的机会以及幼鱼移居海洋的能力可能有助于种群恢复。尽管生命早期阶段的生存对成年种群规模具有潜在的巨大影响，但管理人员和科学家评估离开淡水生态系统的溯河产卵幼鱼数量的能力有限。这些数据对于评估繁殖成功率和栖息地适宜性至关重要，并已被确定为溯河产卵鱼类研究和管理的重中之重。我们开发了最先进的水下视频和计算系统来收集视频来估计幼河鲱鱼的丰度和迁徙时间（拟哈伦鱼;夏芦荟）。我们从 2017 年 6 月到 11 月在纪念碑河（美国马萨诸塞州伯恩）收集了连续视频。我们训练了三种类型的神经网络模型来检测和计数视频帧中的鱼类，并通过将人数与模型输出进行比较来评估模型性能。我们的顶级模型评估了存在和缺席（F1 = 87%）并对鱼进行计数（计数误差 9.4%），准确度与人类计数器相当（F1 = 88%）。我们的系统能够收集迁徙幼鱼的准确计数，这将提供与产卵成鱼数量、系统特定生产力以及产卵和育苗栖息地适宜性相关的关键信息。视频收集系统和计算模型都可以转移到其他地点和其他物种，跟踪幼年迁徙可以为管理工作提供信息。