Stable C and N isotopes and five trace metal concentrations in the tissues of four odontocetes around Taiwan, Northwestern Pacific Ocean

The concentrations of iron (Fe), zinc (Zn), copper (Cu), manganese (Mn) and cadmium (Cd) were analyzed in muscle, liver, kidney and lung tissue samples, and stable carbon and nitrogen isotopes were measured in the muscle tissue samples from 10 Kogia breviceps (Kb), 3 Steno bredanensis (Sb), 14 Tursiops truncatus (Tt) and 4 Tursiops aduncus (Ta), collected from waters around Taiwan from 2003 to 2020.The results indicated that Kb and Sb primarily inhabit deeper and offshore regions, while Tt and Ta are found in shallower, nearshore areas. Kb primarily feed on deep-sea cephalopods, whereas the other three consume fish and a variety of marine invertebrates. In Kb, kidney Fe concentrations increased with body length, suggesting enhanced deep-diving capabilities as they mature-a trend not observed in the other species. Elevated Zn concentrations in muscle and Mn concentrations in kidney tissues of young Kogiids and Delphinids likely reflect physiological demands during early development. Furthermore, the high mean Cd concentrations detected in the muscle and kidney tissues of Tt and Sb indicate a rising trend in Cd pollution in the north-western Pacific Ocean over the past two to three decades.