Diversity in habitat use by the East Asian fourfinger threadfin Eleutheronema rhadinum revealed by otolith Sr:Ca and Ba:Ca profiles

Abstract

Determining the movement and migration patterns of fish between different environments is crucial for understanding the distribution of fish populations and the ecological mechanisms underlying their spatial dynamics. This study is the first to employ otolith Sr:Ca and Ba:Ca profiles to elucidate habitat use by the commercially valuable estuarine species Eleutheronema rhadinum. Age 1+ fish were present in samples from the East China Sea and South China Sea, caught off China in October to December of 2019. Characterization of both otolith element profiles through a quantitative approach suggested migration plasticity for E. rhadinum, especially during the first year. However, the Ba:Ca profile revealed a more distinct pattern of habitat use compared with the Sr:Ca profile, suggesting that the Ba:Ca ratio is more appropriate for life-history reconstruction of this species. Most individuals appeared to be estuary-dependent, with some appearing to have entered fresh water for a short time during their first year of life. After their first winter, individuals tended to move into coastal waters, and most apparently overwintered in the marine environment. Knowledge of the diverse life-history strategies of this valuable species at different life stages should be incorporated into future conservation and management efforts.