ABSTRACT
Marine mammal populations, such as the St. Lawrence beluga whales (Delphinapterus leucas), the Mediterranean Sea striped dolphins (Stenella coeruleoalba), the US Atlantic coast and Gulf of Mexico bottlenose dolphins (Tursiops truncatus) and the Baltic gray seals (Halichoerus grypus), show high concentrations of environmental contaminants which have been associated with disease in these populations (Baker, 1984; Kuehl et al., 1991; Leonzio et al., 1992; Olsson et al., 1994; Kuehl and Haebler, 1995; Borrell et al., 1996; Jenssen, 1996; Munson et al., 1998). The St. Lawrence beluga whales form a small endangered population (Committee on the Status of Endangered Wildlife in Canada, COSEWIC) that inhabits the St. Lawrence estuary and the Saguenay Fjord (Michaud, 1993). Both these regions are contaminated with environmental contaminants including polycyclic aromatic hydrocarbons (PAHs), organochlorine compounds (OCs) and mercury, which originate from atmospheric transport, a variety of local industries, such as aluminum refineries and chloro-alkali plants, municipal effluents, the Great Lakes, St. Lawrence tributaries, and soil erosion (Martel et al., 1986; Dalcourt et al., 1992; Gobeil and Cossa, 1993; Pham et al., 1993; Gearing et al., 1994; Quémarais et al., 1994). Necropsies of dead stranded whales have shown a high prevalence of tumors, non-neoplastic lesions and opportunistic diseases (DeGuise et al., 1994, 1995; Martineau et al., 1994, Chapter 13 in this volume). Cancer has been diagnosed as the principal cause of death in 18 per cent of 73 examined carcasses and the annual crude cancer rate was estimated to be 233/100 000; higher than in many human and domestic animal populations (DeGuise et al., 1994, 1995; Martineau et al., 1999 and more recent data in this monograph). Population modeling, field studies and necropsy observations of female reproductive organs have suggested a
lower reproductive rate in this population than in Arctic populations (Béland et al., 1988, 1993; Michaud, 1993). High concentrations of polychlorinated biphenyls (PCBs), OC compounds and mercury have been found in tissues of the St. Lawrence beluga whales (Muir et al., 1990, 1996). On the contrary, Arctic beluga whales have low concentrations of environmental contaminants (Muir et al., 1990). Benzo[a]pyrene (B[a]P)-DNA adducts have been detected by high pressure liquid chromatography (HPLC) fluorescence analysis in St. Lawrence beluga whales, but not in Arctic beluga whales (Martineau et al., 1994; Mathieu et al., 1997). However, B[a]P-DNA adducts were detected in Arctic beluga whales using competitive enzyme-linked immunosorbent assay (ELISA) with a fluorescent endpoint (Mathieu et al., 1997). It remains to be determined whether this immunochemical assay will detect higher levels of B[a]P-DNA adducts in St. Lawrence beluga whales. Moreover, no gross evidence of cancer has been found in approximately 50 Arctic beluga whale carcasses sampled for routine biological purposes (David J. St. Aubin, 30 October 1997, personal communication). Factors such as tumor induction, tumor promotion and immunosuppression induced by environmental contaminants have been proposed to explain the elevated cancer prevalence in the St. Lawrence population (DeGuise et al., 1994, 1995). Environmental contamination may also be involved in the high prevalence of cancer in California sea lions (Zalophus californianus) (Gulland et al., 1996).
