Study on the Life History and Critical Habitat Identification of <i>Coilia nasus</i> From the Yellow River Based on Microchemical Characteristics of Otolith

To reconstruct the life history of Coilia nasus in the Shandong section of the Yellow River, an electron probe microanalyzer (EPMA) was employed to analyze the Sr and Ca values in the otoliths of 12 individuals collected from Pangkou Bay. The results indicated that the life history of C. nasus is complex and diverse, the individuals in this study can be categorized into five distinct patterns. Pattern I includes P1, P2, P3, and P4, whose life history tracks indicate hatching in brackish water near the Yellow River estuary; after approximately 1 year, they begin to migrate along the Yellow River to Pangkou Bay for spawning. Pattern II encompasses P9, P12, and P13, which hatch in freshwater habitats; as these individuals grow, there is an abrupt change from Stage 1 to Stage 2, but their life history does not extend to marine habitats with high Sr/Ca values, and after about 1 year, they migrate along the Yellow River to Pangkou Bay for spawning. Pattern III includes P6, P8 and P10, which also hatch in freshwater habitats and experience abrupt changes; however, the mapping analysis reveals a large area of red and yellow concentric rings, indicating a history of seawater habitat and an extension of their life history to Laizhou Bay. Pattern IV is represented by P11, whose living environment was relatively stable, with no significant abrupt changes and no migratory life history characteristic, which presumed to be a freshwater settlement type that passively entered the Yellow River due to the flood season of Dongping Lake. Pattern V is exemplified by P7, whose analysis results show two trips to freshwater and brackish water habitats, both of which produced significant pattern changes which indicates that it conducted a reproductive migration at the first instar, swam to the Yellow River estuary after spawning, and migrated to Pangkou during the reproductive period of the following year to lay eggs until it was captured. This study demonstrates that most individuals in Pangkou Bay are of the migratory type. Compared with the sexual maturity of individuals in other waters of the Yangtze River basin, Pangkou Bay is identified as an important spawning ground for the migratory type of C. nasus .