Alewife Alosa pseudoharengus and Blueback Herring A. aestivalis—collectively referred to as river herring—exhibit complex life histories, exploiting freshwater and marine biomes to complete their life cycles. We investigated distribution patterns of river herring in the Penobscot River estuary, Maine, USA, from April through September in 2012 and 2013 and found both species in relatively low-salinity portions of the estuary in all months sampled. River herring made up the majority of samples in terms of abundance and biomass for most months. We developed age–length keys for monthly catches and found consistent presence of age-1 and age-2 river herring, especially during spring. We found seasonal patterns in age distribution with age-1 fish and older most abundant in spring and summer and age-0 fish only occurring in late summer through fall. These observations provide direct evidence of life cycle diversity for juvenile river herring, complementing other recent observations in other parts of their native range. Lastly, our findings suggest further consideration should be given to the importance of connectivity between marine, estuarine, and freshwater habitats for age-1 and age-2 river herring and to the more complex ecological roles of age-1 and age-2 river herring given their intermediate trophic level and presence in relatively fresh components of the Penobscot River estuary.

中文翻译：

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缅因州佩诺布斯科特河口河鲱鱼生命周期多样性的证据

灰西鲱鲱和蓝背西鲱一个。夏令时——统称为河鲱——展示了复杂的生活史，利用淡水和海洋生物群落来完成它们的生命周期。我们调查了 2012 年和 2013 年 4 月至 9 月美国缅因州佩诺布斯科特河口河鲱鱼的分布模式，并在所有采样月份中发现这两种物种都位于河口盐度相对较低的部分。在大多数月份，河鲱鱼在丰度和生物量方面构成了大部分样本。我们为每月捕获量开发了年龄长度密钥，并发现 1 岁和 2 岁河鲱鱼一致存在，尤其是在春季。我们发现年龄分布的季节性模式，1 岁及以上的鱼在春季和夏季最丰富，0 岁的鱼只出现在夏末到秋季。这些观察结果提供了幼年河鲱生命周期多样性的直接证据，补充了最近在其原产地其他地区的其他观察结果。最后，我们的研究结果表明，应进一步考虑海洋、河口和淡水栖息地对 1 岁和 2 岁河鲱鱼的重要性，以及 1 岁和 2 岁河鲱鱼更复杂的生态作用考虑到它们的中等营养水平和存在于佩诺布斯科特河河口相对较新鲜的部分。