Abstract:Coilia nasus, a historically significant fish species in the Yangtze River, has experienced a significant decline because of overfishing and habitat degradation. As an anadromous fish, C. nasus traverses different habitats over large geographic areas, making effective conservation difficult. Tracing their natal origin and lifelong habitat useage at the individual and population levels will enhance our ability to protect critical habitats of this anadromous fish. The migratory life history of C. nasus across freshwater, estuarine, and marine environments can be determined by analyzing otolith Sr/Ca ratios. However, difficulties remain in tracking their natal origins and identifying transitions between freshwater habitats during the early stages of their development. The use of otolith 87Sr/86Sr isotopic ratios offers a robust approach for tracing the natal origins and migration patterns of C. nasus. The Sr isotope (87Sr/86Sr) composition of the otoliths was analyzed using laser ablation multi-collector inductively coupled plasma mass spectrometry (LA-MC-ICP-MS) to confirm the hatching grounds and life histories of C. nasus in the Poyang Lake. In July and August 2023, a total of ten adult C. nasus and three adult C. brachygnathus were collected from the Duchang area of the Poyang Lake, Jiangxi Province, China. The otolith 87Sr/86Sr profiles from the core to the edge displayed minor fluctuations of approximately 0.71448, indicating that the three C. brachygnathus individuals reside in the Poyang Lake. The 87Sr/86Sr ratio of the otolith core region of nine C. nasus was close to 0.71448, indicating that they hatched in the Poyang Lake and subsequently returned to the lake (because they were caught in the Poyang Lake). Among these individuals, four migrated out of the Poyang Lake during their larval stage and five migrated during their juvenile stage. One individual exhibited an average 87Sr/86Sr ratio of 0.71078 in its first segment, suggesting that it was born in the main channel of the Yangtze River and then strayed into Poyang Lake after its sea life history. The results demonstrated the objectivity, accuracy, and stability of otolith 87Sr/86Sr ratio as a reliable geographical indicator for identifying the natal origin of C. nasus in the Poyang Lake. Furthermore, these findings shed light on habitat shifts between the Poyang Lake and the main Yangtze River channel, emphasizing the diverse timing of early life migration from the Poyang Lake. Consequently, despite being a preliminary study, this study demonstrates the potential of using Sr isotopes to distinguish between natal origins and freshwater habitats. This approach is significant within the context of a decade-long fishing prohibition in the Yangtze River, as it facilitates the assessment of species recovery and management while contributing to broader ecological and conservation insights.