Abstract

A population of approximately 650 beluga (Delphinapterus leucas) inhabits a short segment of the St. Lawrence Estuary. Over 17 years (1983-1999), 129 (or 49%) of 263 St. Lawrence estuary (SLE) beluga carcasses reported stranded have been examined. The major primary causes of death were respiratory and gastro-intestinal infections with metazoan parasites (22%), cancer (18%) and bacterial, viral and protozoan infections (17%).

Cancer was observed in 27% of examined adult animals found dead, a percentage similar to that found in humans. The estimated annual rate of all cancer types (AR) (163/100,000 animals) is much higher than that reported for any other population of cetacean and is similar to that of man, and to that of hospitalized cats and cattle. The AR of cancer of the proximal intestine, a minimum figure of 63/100,000 animals, is much higher than that observed in domestic animals and humans, except in sheep in certain parts of the world, where environmental contaminants are believed to be involved in the etiology of this condition. The human population living in proximity of the SLE beluga habitat is affected by higher rates of cancer than people in the rest of Quebec and Canada and some of these cancers have been epidemiologically related to polycyclic aromatic hydrocarbons (PAHs) produced by local aluminum factories. Considered with the above observations, the exposure of SLE beluga to PAH and their contamination by these compounds suggest that PAHs are involved in the etiology of cancer of the digestive system in these animals.

Acknowledgements

The authors wish to thank Drs. P. B. and, S. DeGuise, S. Lair, R.J. Letcher, L. Measures, Dr. R. Norstrom for helpful discussions, and R. Plante and C. Guimont (Filmar) for recovering and transporting carcasses. We acknowledge the financial support of World Wildlife Fund Canada, Alcan, Fisheries and Oceans Canada, Fondation de la Faune du Quebec, Societe des Pares du Quebec, and NSRC.