Chapter VI 



EFFECTS OF POLLUTION ON MARINE MAMMALS 



Marine mammals can be affected directly and 

 indirectly by a variety of environmental contaminants 

 of human origin. These include persistent organic 

 compounds and toxic metals from point and non-point 

 sources, lost and discarded fishing gear and other 

 marine debris, and noise from a variety of anthropo- 

 genic sources. Direct effects include mortality from 

 toxic chemical spills, entanglement in lost and discard- 

 ed fishing gear, and hearing loss caused by loud 

 noises. Indirect effects include decreased survival and 

 productivity due to contaminant-caused decreases in 

 essential prey species. 



Actions taken by the Commission and others with 

 regard to marine debris are described in the Commis- 

 sion's previous report and in the sections of this 

 report concerning Hawaiian monk seals and conserva- 

 tion of marine mammals and their habitats in the 

 Southern Ocean. The following sections of this 

 chapter provide background information and describe 

 efforts by the Commission, in consultation with its 

 Committee of Scientific Advisors, to identify and 

 precipitate actions necessary to minimize threats posed 

 by chemical pollution and noise from various sources. 



Effects of Chemical Contaminants 



Virtually all marine mammals alive today have 

 been exposed to a variety of chemical compounds and 

 trace elements introduced into the marine environment 

 by human activities. Many of these substances enter 

 the marine environment directly as a result of runoff, 

 leakage, dumping, or atmospheric transport. They are 

 also dispersed in the enviroiunent via food webs. As 

 high-order predators, marine mammals (except the 

 sirenians and some baleen whales) can experience the 

 effects of biomagnification. They can acquire rela- 

 tively large burdens of foreign substances by ingesting 

 contaminated prey. Like other air-breathers, marine 

 mammals also are exposed to contaminants via atmo- 



spheric gas exchange. The physiological processes 

 involved in storage, metabolism, and elimination of 

 contaminant burdens are poorly understood. Also, 

 there is great uncertainty about the mechanisms and 

 pathways of contaminant flux in marine environments 

 and food webs. 



The possible effects of chemical contaminants on 

 the health of individual marine mammals and on the 

 welfare of marine mammal populations have received 

 increasing attention over the past three decades, and 

 especially during the last few years. Among the 

 concerns are (1) the apparently increasing incidence of 

 disease outbreaks involving many animals with 

 apparently high burdens of organochlorines or other 

 contaminants; and (2) the growing experimental and 

 other evidence that contaminants often found in 

 marine mammal tissues have deleterious effects on 

 reproduction. Recognizing the growing importance of 

 the problem, the Marine Mammal Commission, the 

 Environmental Protection Agency, the National 

 Marine Fisheries Service, and the National Fish and 

 Wildlife Foundation jointly sponsored a Workshop on 

 Marine Mammals and Persistent Ocean Contaminants. 



The workshop, held in Keystone, Colorado, on 

 12-15 October 1998, was attended by more than 50 

 scientists from seven countries. Their expertise 

 spanned the disciplines of environmental toxicology, 

 environmental chemistry, marine mammal health and 

 husbandry, pathology and disease, physiology, im- 

 munotoxicology, marine mammal population dynamics 

 and ecology, experimental design, and environmental 

 risk assessment. The workshop focused on science 

 rather than policy and was organized by a steering 

 committee with representatives of the Commission, 

 the Biological Resources Division of the U.S. Geolog- 

 ical Survey, the National Marine Fisheries Service, 

 the Environmental Protection Agency, and the aca- 

 demic community. Its objectives were as follows; 



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