Heavy metals, gastrointestinal polymer-related materials, and gut microbiome in an Indo-Pacific bottlenose dolphin (Tursiops aduncus) recovered from a fisheries bycatch-related event in the East China Sea

Incidental cetacean bycatch provides irreplaceable opportunities to investigate population dynamics, mortality, and health. This multidisciplinary study examined morphology, age, gut microbiome, heavy metals, and gastrointestinal polymer-related materials in an immature male Indo-Pacific bottlenose dolphin (Tursiops aduncus, 248 cm, 114 kg, 5 years) accidentally captured in the East China Sea. Morphometrics indicated excellent body condition (BCI = 0.506) and superior dorsal fin shape compared to captive individuals, highlighting the role of natural environments in development. The gut microbiome was dominated by Proteobacteria and Firmicutes, showing segment-specific variation. Heavy metals accumulated mainly as Cd in kidneys and Cu and Zn in liver, with overall levels lower than those in other Chinese marine regions. LDIR analysis indicated the presence of polymer-related materials in the gastrointestinal tract, including reported matches to polyamide and chlorinated polyethylene, which may be associated with fisheries activities. These findings provide critical baseline ecotoxicological data for the East China Sea and underscore the importance of standardized passive biomonitoring networks that transform bycatch events into valuable scientific and conservation resources.