Fish assemblages in large rivers are governed by spatio‐temporal changes in habitat conditions, which must be accounted for when designing effective monitoring programmes. Using boat electrofishing surveys, this study contrasts species richness, catch per unit effort (CPUE), total biomass, and spatial distribution of fish species in the Saint John River, New Brunswick, Canada, sampled during different diel periods (day and night) and macrohabitats (hydropower regulated river and its reservoir) in the vicinity of the Mactaquac (hydropower) Generating Station. Taxa richness, total CPUE, and total biomass were significantly higher during night surveys, resulting in marked differences in community composition between the two diel periods. Furthermore, the magnitude of diel differences in catch rate was more pronounced in lentic than in lotic macrohabitats. The required sampling effort (i.e., number of sites) to increase accuracy and precision of CPUE estimates varied widely between fish species, diel periods, and macrohabitats and ranged from 15 to 185 electrofishing sites. Determining a correction factor to contrast accuracy and precision of day‐ with night‐time surveys provide useful insights to improve the design of long‐term monitoring programmes for fish communities in large rivers. The study also shows the importance of multihabitat surveys to detect differences in the magnitude of diel changes in fish community metrics.

中文翻译：

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调节河中透镜状和水状生境中鱼类种群空间分布的狄尔模式

大河流中的鱼群受栖息地条件的时空变化控制，在设计有效的监测程序时必须考虑这些变化。通过船用电钓鱼调查，本研究在不同的diel时期（白天和黑夜）采样了加拿大新不伦瑞克省圣约翰河的物种丰富度，单位捕捞量（CPUE），总生物量和鱼类物种的空间分布。 Mactaquac（水电）发电站附近的大型栖息地（水电调节河及其水库）。在夜间调查中，分类单元丰富度，总CPUE和总生物量显着较高，导致两个diel时期之间的社区组成存在明显差异。此外，比起抽水的大型栖息地，在镜头上捕获率的迪尔差异的幅度更为明显。为提高CPUE估计的准确性和精确度所需的抽样工作（即地点数量）在鱼类，di鱼期和大型栖息地之间差异很大，范围从15到185个电钓鱼地点。确定用于与白天进行夜间调查的对比准确性和精确度进行对比的校正因子，可以提供有用的见解，以改进大型河流鱼类群落的长期监测程序的设计。这项研究还显示了多生境调查对检测鱼类群落指标中diel变化幅度的差异的重要性。和大型生境，范围从15到185个电捕鱼场。确定用于与白天进行夜间调查的对比准确性和精确度进行对比的校正因子，可以提供有用的见解，以改进大型河流鱼类群落的长期监测程序的设计。这项研究还显示了多生境调查对检测鱼类群落指标中diel变化幅度的差异的重要性。和大型生境，范围从15到185个电捕鱼场。确定用于与白天进行夜间调查的准确性和精确度进行对比的校正因子，可以提供有用的见解，以改进大型河流鱼类群落的长期监测程序的设计。这项研究还显示了多生境调查对检测鱼类群落指标中diel变化幅度的差异的重要性。