||The aims of this study were (1) to investigate the differences of heavy metal concentrations in various cetacean species, (2) to know how the factors including feeding habits, habitats, body lengths, stranded or bycatch affect the accumulation of tissue concentrations of heavy metals in cetaceans, and (3) to compare with previously reported values. Ten different tissues from 9 species were collected from 2001 to 2011 and analyzed for As, Cd, Cu, Fe, Mn and Zn concentrations and isotope values (δ13C and δ15N). These 9 species included Risso’s dolphin (Grampus griseus), Pantropical spotted dolphin (Stenella attenuata), Chinese white dolphin (Sousa chinensis), Fraser’s dolphin (Lagenodelphis hosei), Dwarf sperm whale (Kogia sima), Omura's whale (Balaenoptera omurai), Pygmy killer whale (Feresa attenuata), False killer whale (Pseudorca crassidens) and Finless porpoise (Neophocaena phocaenoides).|
Both δ13C and δ15N showed significant variation among species (p<0.05). The highest δ13C values (-13.4 ‰ and -14.3 ‰) were found in Finless porpoise and Chinese white dolphin, whereas the lowest δ13C values (-16.9 ‰ and -16.9±0.39 ‰) were found in Omura’s whale and Fraser’s dolphin. The highest δ15N values (14.9 ‰ and 14.6 ‰) were found in Chinese white dolphin and False killer whale, whereas the lowest δ15N values (10.9 ‰) were found in Omura’s whale. Heavy metal analysis indicated that extremely high Fe (7169 μg/g dry wt. in liver) and Mn (87.5 μg/g dry wt. in liver) levels were found in a pregnant Dwarf sperm whale. The highest Zn levels were found in the liver (400.7 μg/g dry wt.) and kidney (288.0 μg/g dry wt.) of Chinese white dolphin, and the highest Cu level was found in Omura’s whale, the only baleen whale. Significant positive or negative correlations between certain elements (Cd and As) and factors (body length and δ15N) were found in Risso’s dolphin. A negative correlation between body length and δ15N in Risso’s dolphin was also observed. Multidimensional Scaling (MDS) and cluster analysis showed that stranded individuals had higher Fe and Cd levels than bycatch specimens.
The results of this study suggest that heavy metal concentrations in cetacean tissues are highly varied due to different species, feeding habits, habitats and physiological status such as pregnancy. Furthermore, via the correlation analysis between renal cadmium / hepatic arsenic concentrations and body length / δ15N in Risso’s dolphins, we can conclude that male Risso’s dolphin would gradually move to offshore to feed on more oceanic cephalopods with increasing age. Also, both stranded and bycatch Risso’s dolphin in this study exhibit higher heavy metal concentrations than those collected in 1994 and 1995 (except Mn in muscles), providing an early warning of the heavy metal pollutions in the surrounding waters of Taiwan.