LAUSR

Eels have fascinated biologists for centuries, due to their amazing long-distance migrations between freshwater habitats and very distant ocean spawning areas. The migratory life histories of the Japanese eel, Anguilla japonica, in the waters of south China are not very clear, despite its ecological importance, and the need for fishery regulation and management. In this study, strontium (Sr) and calcium (Ca) microchemical profiles of the otoliths of sliver eels were measured by X-ray electron probe microanalysis (EPMA) based on data collected from different habitats (including freshwater and brackish habitats), in the large subtropical Pearl River. The corresponding habitat preference characteristics were further analyzed using redundancy analysis (RDA). A total of 195 Japanese eels were collected over six years. The collected individuals ranged from 180 to 771 mm in total length and from 8 to 612 g in body weight. Two-dimensional pictures of the Sr:Ca concentrations in otoliths revealed that the A. japonica in the Pearl River are almost entirely river eels, spending the majority of their lives in freshwater without exposure to salt water. While the catadromous migration time has delayed about one month in the Pearl River estuary in the past 20 years. RDA analysis further indicated that juveniles and adults preferred water with high salinity and high tide levels. Youth preferred habitats with high river fractals. Our findings contribute to a growing body of evidence, and showing that the eels extremely scarce currently and conservation measures against them are imminent, including the protection of brackish and freshwater areas where they live in south China.