The Raffles Bulletin of Zoology (2002)


Data on causes of death for finless porpoise (Neophocaena phocaenoides) specimens stranded in Hong Kong between 1995 and 2000 were evaluated. We diagnosed several causes of death, including fishing net entanglement (44%), vessel collision (17%), reproductive abnormalities (17%), parasitic infections (17%), and shark attack (5%). The incidence of net entanglements may have increased in recent years. We also examined the levels of five types of environmental contaminants of particular concern (DDTs, PCBs, HCHs, BTs, and Hg). Organochlorine concentrations generally increased with age in males, but decreased with age in females, the latter likely due to the reproductive transfer of these lipophilic compounds to the offspring during gestation and lactation. Mercury levels increased exponentially with age in both sexes. Organochlorine pesticide (DDT), and to a lesser extent, polychlorinated biphenyl (PCB) concentrations were extremely high in some individuals. There was some evidence for higher (but not statistically significant) DDT and HCH concentrations in specimens classified as in ‘poor’ health. This suggests that these organochlorines may indeed be affecting the health of Hong Kong finless porpoises. Mercury levels were also very high, and were in the range of concentrations previously found to be associated with liver disease in bottlenose dolphins. However, the levels of mercury were similar in specimens classified both as in ‘good’ and ‘poor’ health. Although much further work needs to be done to clarify the factors related to mortality and morbidity of finless porpoises in Hong Kong, this preliminary study suggests that fishing net entanglement may be the primary human-related cause of death. Further, there is now sufficient evidence to point to the damaging effects of some environmental contaminants on these animals. We suggest that efforts to mitigate these effects be implemented immediately to ensure the conservation of the porpoise population.