Mercury bioaccumulation and trophic dynamics in marine fishes off Taiwan revealed by stable isotopes

This study examines total mercury (THg) concentrations and stable isotope ratios (δ¹³C and δ¹⁵N) in 49 specimens from 12 pelagic and mesopelagic species collected from Taiwanese fisheries. THg levels ranged from 0.01 to 0.17 μg g^-1 wet weight (w.w.; 0.05 ± 0.04 μg g^-1), with δ¹⁵N values from 8.5 to 12.9 ‰ (10.9 ± 1.2 ‰), and δ¹³C from -19.1 to -15.4 ‰ (-16.7 ± 0.9 ‰). Most species exhibited strong positive correlations between body length and THg, indicating size-dependent bioaccumulation, whereas Cephalopods (e.g., Uroteuthis edulis) and Cutlassfish (e.g. Trichiurus japonicas) showed weaker trends, reflecting distinct life histories. THg also increased with δ¹⁵N, supporting trophic-level biomagnification and species with higher δ¹⁵N values tended to occupy deeper habitats, indicating depth-related enrichment. Biomagnification slopes and trophic magnification factor (TMF) were slightly higher in the western (WNPO) than in the eastern (ENPO), suggesting more efficient Hg transfer through food webs beside Hg pollution. Strong THg-δ¹⁵N relationships (R² = 0.8) across regions highlight the combined influence of trophic dynamics and oceanographic conditions on Hg accumulation, with important implications for ecosystem-based fishery management and seafood safety.