Otolith Strontium Isotope (87Sr/86Sr) Reveals Mixed Life Histories of Coilia brachygnathus in the Middle–Lower Yangtze River Floodplain
2025
Zhongya Xuan | Yinping Wang | Sheng Wang | Yanping Yang | Chongrui Wang | Silei Liu | Kai Liu
Life-history plasticity allows fishes to exploit heterogeneous freshwater networks, and proactive habitat selection enhances their capacity to cope with climatic and human-induced stressors. Coilia brachygnathus, long regarded as a freshwater resident, nevertheless has a poorly understood habitat use and selection. We reconstructed habitat use of C. brachygnathus across the middle-lower Yangtze by coupling water 87Sr/86Sr baselines with otolith 87Sr/86Sr transects. We used 60 water samples, compiled published datasets, and measured additional water samples from the mainstem, major tributaries, and connected lakes. In situ 87Sr/86Sr profiles were smoothed with generalized additive models, revealing significant within-profile variation for all fish. Two modes emerged: (i) residents, whose otolith values remained within local water ranges, consistent with limited movement: and (ii) migrants, whose profiles departed from local baselines, indicating exchanges among lakes, tributaries, and the mainstem. Several fish captured at Anqing and Zhenjiang possess Poyang-like core signatures that declined to mainstem values, while bidirectional shifts were common in the Dongting-Xiang system. These results overturn the residency paradigm, demonstrate flexible partial migration, and indicate proactive habitat selection in the face of environmental change, thereby supporting management that maintains river&ndash:lake connectivity and quantifies lake contributions to mainstem stocks.
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