Age-structured otolith chemistry profiles revealing the migration of Conger myriaster in China Seas

Abstract

Conger myriaster is an eel species of considerable economic value in China Seas and around the Korean Peninsula and Japan, but its migration pattern remains largely unknown. This study used otolith microchemistry to investigate the migration and spawning of C. myriaster in the Yellow Sea and East China Sea. Samples were collected from three geographic regions, i.e. Middle Yellow Sea (QD), South Yellow Sea (DS) and East China Sea (ZS), and the micro-chemical compositions of otoliths were analyzed using laser ablation inductively coupled plasma mass spectrometry to produce continuous life history profiles of 4-year classes. The ratios of trace elements were analyzed with growth rings of otoliths to infer age-specific life-history profiles. Hierarchical cluster analysis showed no obvious partitioning in otoliths cores among samples, suggesting a similar environment at birth in these fish. The chemical compositions showed non-significant differences among sampling areas from core to metamorphosis zone, beyond which Ba:Ca ratio showed significant differences in the QD compared to other regions within the first year. This suggested that individuals might experience similar environmental conditions in the early life stages, and, during metamorphosis, QD individuals separated from the population and moved toward coastal waters of Shandong peninsula. The ZS and DS individuals shared similar chemical composition within the first year but differed in Ba:Ca and Sr:Ca ratios afterwards, suggesting a separation of the two groups at ages 1−2. The chemical signatures of the otoliths provide information on the spawning and separation of C. myriaster, which may contribute to the management of the eel fisheries.