In freshwater fishes, the nitrogen and carbon stable isotopes ratios in tissues commonly reflect the environment in which a fish is feeding, assimilated through its diet. For many species, small‐bodied or younger individuals generally feed lower in the food chain, while large‐bodied mature individuals feed at higher trophic levels. This is reflected in the stable isotope (SI) ratios within fish tissue, with large‐bodied fish typically exhibiting more enriched isotope signatures. However, an inverse relationship has been seen in recently‐hatched, premigratory juvenile fishes of anadromous maternal stock. This has been documented previously in some salmonids, and it is due to the maternal contribution of marine‐derived nitrogen to juvenile fish, which fades with isotopic turnover as they grow and assimilate energy from freshwater food webs. However, this phenomenon has not been previously documented for wild Pacific salmonids, as we present here. We found that the isotope ratios of premigratory juvenile Chinook Salmon Oncorhynchus tshawytscha were elevated at posthatch, declined with increased body size, and converged with those of sympatric freshwater resident Brown Trout at 3.39 g body mass or 79 mm TL (at approximately 48–84 d posthatch). Given our findings, researchers should account for the lingering maternal isotopic enrichment of premigratory juvenile salmon to avoid introducing bias into SI‐based freshwater food web studies. Additionally, the maternal life history (sea‐run or resident) for the progeny of partially anadromous Pacific salmonids can likely be classified by examining SI information, which is supported by our results and by previous research on other anadromous salmonids. Therefore, SI analysis could be a useful tool for characterizing the relative contribution of anadromous females in partially migratory populations of other Pacific salmonids (e.g., steelhead Oncorhynchus mykiss) to help with the management and conservation of these sensitive fish species.

中文翻译：

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母体转移的氮和碳对奇努克鲑鱼稳定同位素比的影响

在淡水鱼中，组织中氮和碳的稳定同位素比率通常反映了通过饮食吸收的鱼的摄食环境。对于许多物种，小体或更年轻的个体在食物链中的饲料通常较低，而大体成熟的个体在营养水平上的饲料较高。这反映在鱼组织内稳定的同位素（SI）比中，大体鱼类通常表现出更丰富的同位素特征。但是，在最近孵化的，成年后母本种群处于繁殖前期的幼鱼中发现了一种反比关系。以前在某些鲑鱼中已有记载，这是由于海洋来源的氮对幼鱼的母体贡献，随着鱼类的生长和吸收淡水食物网中的能量，其随着同位素转换而消失。然而，正如我们在此处介绍的那样，野生太平洋鲑鱼的这种现象以前没有记录。我们发现，迁徙前的奇努克鲑鱼的同位素比Oncorhynchus tshawytscha在孵化后升高，随体型增加而下降，并与同居淡水居民布朗鳟鱼（3.39 g体重或79 mm TL）（在孵化后约48-84 d）收敛。鉴于我们的发现，研究人员应考虑到迁徙前幼鲑的母亲同位素残留持续存在，以避免在基于SI的淡水食物网研究中引入偏见。此外，通过检查SI信息，可以对部分弱水生太平洋鲑鱼的后代的孕产妇生活史（无论是海上的还是常住的）进行分类，我们的研究结果以及先前对其他无水鲑鱼的研究都支持了SI信息。因此，SI分析可能是表征在其他太平洋鲑鱼（例如，head鱼）的部分迁徙种群中弱势女性相对贡献的有用工具。Oncorhynchus mykiss），以帮助管理和保护这些敏感鱼类。