Otolith microchemistry provides valuable information about the environmental history of individual fish, but few studies have considered the influence of population or stock on life history traits. This study used the Sr/Ca ratio as an index of habitat use of spinyhead croaker Collichthys lucidus from 2 different populations (northern and southern China populations), including lifetime otolith microchemistry profiles (n = 63 fish) and determinations of natal habitat selection (n = 352 fish). The otolith data revealed 3 life history patterns in C. lucidus: Pattern 1 individuals spent most of their lifetime (>95%) in mesohaline waters (Sr/Ca range: 3-7 mmol mol-1), particularly during early growth; Pattern 2 individuals migrated from hyperhaline waters (Sr/Ca ≥ 7 mmol mol-1) to mesohaline waters; and Pattern 3 individuals migrated from oligohaline waters (Sr/Ca < 3 mmol mol-1) to mesohaline waters. Pattern 2 and Pattern 3 were specific to the northern and southern China populations, respectively, and Pattern 1 was shared by the 2 populations. The otolith core Sr/Ca ratios showed that most C. lucidus selected mesohaline waters as their natal habitat (i.e. 90.6% of 352 total individuals); 12.5% (19 of 152) selected hyperhaline waters and fell within the northern China population, and 7% (14 of 200) selected oligohaline waters and fell within the southern China population. These results indicate that life history diversity exists in this species, as the pattern of habitat use largely differed between the northern and southern China populations. The overall findings highlight that the behavior of different populations should be considered when determining fish migration histories.

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.