Itakura Hikaru, Arai Kohma, Kaifu Kenzo, Shirai Kotaro, Yoneta Akihito, Miyake Yoichi, Secor David H, Kimura Shingo
Graduate School of Frontier Sciences, The University of Tokyo, Chiba, Japan.
Atmosphere and Ocean Research Institute, The University of Tokyo, Chiba, Japan.
J Fish Biol. 2018 Nov;93(5):805-813. doi: 10.1111/jfb.13782.
The natural occurrence of Japanese eels Anguilla japonica in Japan's highly altered catchments is a critical measure of habitat restoration and ecosystem health, yet this metric may be obscured by the incidence of co-occurring cultured eels. Distribution of wild and stocked A. japonica in the lower reaches of the Tone River cachment was investigated using otolith oxygen and carbon stable-isotope ratios (δ O and δ C). We developed a discrimination model to classify wild and cultured eels for 560 individuals and applied it to eels captured in the lower reaches of the Tone River catchment. Wild eels were found at all study sites of this part of the catchment, indicating natural recruitment of the species occurred from the estuary to third-order streams at least as far as Lake Imbanuma. The proportion of wild eels ranged from 86 to 100% at river and stream sites and was only 23% at upstream Lake Imbanuma sites. This difference probably depends on whether or not eels were released near the corresponding site. More than 50% of stocked eels occurred at sites proximate to release locations, indicating limited dispersal by cultured eels.
日本鳗鲡在日本高度改变的集水区中的自然出现情况，是栖息地恢复和生态系统健康的一项关键指标，然而这一指标可能会因同时出现的养殖鳗鱼而变得模糊不清。利用耳石氧和碳稳定同位素比率（δO和δC），对利根川集水区下游野生和放流的日本鳗鲡分布情况进行了调查。我们建立了一个判别模型，对560条个体的野生和养殖鳗鱼进行分类，并将其应用于在利根川集水区下游捕获的鳗鱼。在该集水区这一部分的所有研究地点都发现了野生鳗鱼，这表明该物种至少从河口到三级溪流（一直到印幡沼）都有自然补充。在河流和溪流地点，野生鳗鱼的比例在86%至100%之间，而在上游的印幡沼地点仅为23%。这种差异可能取决于鳗鱼是否在相应地点附近放流。超过50%的放流鳗鱼出现在靠近放流地点的位置，这表明养殖鳗鱼的扩散有限。
