Japanese eels (Anguilla japonica) utilize a broad range of habitats along the marine-freshwater ecotone during their growth phase in inland waters. This study aimed to analyze the foraging behavior of yellow-phase Japanese eels in connected fresh- and brackish water habitats and to connect foraging behavior and habitat use through the analysis of carbon (δ13C) and nitrogen (δ15N) stable isotopes. Stomach contents of eels collected in fresh- and brackish waters were analyzed to identify food sources. Values of δ13C and δ15N were analyzed in eels and their potential food sources, and used to predict the recent foraging patterns of eels in the Matsukawa-ura, a brackish water lagoon, and in three freshwater tributaries. Eels preyed on the benthic river community and the mudflat community of the lagoon. Gobiid fishes were found to be an important food source for eels in fresh- and brackish water habitats, while Japanese mitten crabs (Eriocheir japonica) and shore crabs (Hemigrapsus spp.) were major prey in fresh- and brackish waters respectively. δ13C values of potential eel prey differed significantly between fresh- and brackish waters and were used to classify three recent patterns of foraging by the 73 eels included in this study: 1) freshwater foraging, 2) brackish water foraging, and 3) multiple-habitat foraging. The data suggested that some eels recently or frequently moved between fresh- and brackish water habitats while others demonstrated a higher fidelity to either fresh- or brackish waters. Isotopic characteristics of prey in the respective foraging habitats revealed the plasticity of habitat use of yellow eels in the study area. This study demonstrates an integrated approach to study habitat use and foraging behavior of eels. Furthermore, the study underlines the need to consider freshwater and estuarine habitats and the connectivity between them for eel management and conservation.

中文翻译：

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黄相日本鳗在淡水和微咸水相连生境之间的觅食行为

日本鳗鲡（Anguilla japonica）在内陆水域的生长阶段利用了沿海洋-淡水交错带的广泛栖息地。本研究旨在通过对碳（δ13C）和氮（δ15N）稳定同位素的分析，分析黄相鳗在相连的淡水和微咸水栖息地的觅食行为，并将觅食行为与栖息地利用联系起来。分析在淡水和微咸水中收集的鳗鱼的胃内容物以确定食物来源。对鳗鱼及其潜在食物来源的 δ13C 和 δ15N 值进行分析，并用于预测最近在松川浦、咸水泻湖和三个淡水支流中鳗鱼的觅食模式。鳗鱼捕食底栖河流群落和泻湖泥滩群落。戈壁鱼被发现是淡水和咸水栖息地鳗鱼的重要食物来源，而日本绒螯蟹 (Eriocheir japonica) 和岸蟹 (Hemigrapsus spp.) 分别是淡水和咸水水域的主要猎物。潜在鳗鱼猎物的 δ13C 值在淡水和咸水水域之间存在显着差异，并被用于对本研究中包括的 73 条鳗鱼最近的三种觅食模式进行分类：1) 淡水觅食，2) 咸水觅食，3) 多栖息地觅食。数据表明，一些鳗鱼最近或经常在淡水和咸水栖息地之间移动，而其他鳗鱼则表现出对淡水或咸水的更高保真度。不同觅食生境中猎物的同位素特征揭示了研究区黄鳗生境利用的可塑性。本研究展示了一种研究鳗鱼栖息地利用和觅食行为的综合方法。此外，该研究强调需要考虑淡水和河口栖息地以及它们之间的连通性，以进行鳗鱼管理和保护。