Pollution Is Blamed for Killing Whales in St. Lawrence

Pollution from industrial activity along the St. Lawrence River and its tributaries, including the Great Lakes, is causing disease, premature death and a declining birth rate among the white beluga whales in the river, according to Canadian researchers.

The St. Lawrence beluga population, estimated at around 5,000 at the beginning of this century and at about 1,200 after commercial whaling ended in the 1950's, is now believed to be about 450.

Concerned scientists point out that the organisms upon which the whales feed have also been found to be polluted, and note that the area has Canada's highest level of birth defects, although no direct cause-effect relationship has been shown.

Other marine mammals in the same stretch of the St. Lawrence, including harbor porpoises and seals, had been found to have high levels of contaminants in their tissue. Scientists say, however, that there is insufficient data to tell whether these animals are declining in number.

Autopsies of dead belugas washed onto the banks of the river have found very high levels of more than 30 hazardous chemical pollutants, including DDT, polychlorinated biphenyls or PCB's, the pesticide Mirex, metals such as mercury and cadmium, and polycyclic aromatic hydrocarbons similar to those found in cigarettes and regarded as cancer-causing agents.

The diseases found in the 72 dead whales examined so far include bronchial pneumonia, hepatitis, perforated gastric ulcers, pulmonary abscesses and even a case of bladder cancer. A majority of the whales appear to have died from septicemia, or blood poisoning, which killed them because their immune systems failed.

Dr. Joseph E. Cummins, a professor of genetics at the University of Western Ontario in London, Ont., said that the immune system deficiency was triggered by the toxic substances ingested by the whales. When the chemicals are metabolized in the whales' tissues, they attach themselves to the genetic material.

Dr. Cummins said he had reviewed the available scientific literature on the contamination of animals by toxic substances and added, ''I have come to the conclusion that the St. Lawrence beluga is the most polluted mammal on earth.''

The beluga, or Delphinapterus leucas, is not the great white whale hunted by Captain Ahab. Largely a denizen of the Arctic, it is white, but small as whales go, reaching a length of 20 feet. Its voice, a sweet, musical trill, caused whalers of an earlier day to dub it the ''sea canary.''

There are an estimated 30,000 belugas in Arctic Canada as well as populations off the coasts of Alaska, Iceland and the Soviet Union. But the St. Lawrence belugas are an isolated, declining population that was given endangered status by the Canadian Government in 1983. Once ranging from Quebec City well into the Gulf of St. Lawrence, the St. Lawrence belugas are now limited to a short stretch of river on both sides of the mouth of Saguenay River, about 100 miles north of Quebec City.

Leone Pippard, a Canadian writer, has studied, photographed and lobbied for the St. Lawrence belugas for 15 years. The whales were overhunted starting in the beginning of the century until commercial whaling ended in the 1950's, she said. Then, in the 50's and 60's, hydroelectric plants built along tributaries of the St. Lawrence caused changes in the salinity of the river and in the numbers and kind of fish and other marine organisms upon which the beluga feed. 'Most Devastating Blow'

But pollution is the ''most devastating blow,'' she said.

A spokesman for the Canadian Department of Fisheries and Oceans said that there was insufficient data to say conclusively that toxic substances are the chief cause of the decline of the beluga. Yvan Vigneault, who heads the fish habitat division in the department's Quebec office, said pleasure boats and the hydropower dams could also be factors.

But a number of scientists studying the whales are convinced that the toxic substances are the greatest pressure on the remaining beluga population in the St. Lawrence.

Dr. Pierre Beland, a biologist who is science director of the St. Lawrence National Institute of Ecotoxicology, a private research group, is one of the scientists who has intensively studied the pathology of dead belugas beached along the St. Lawrence. He said that many of the pollutants found in the whale tissues could be traced to their sources. For example, he said that there were large quantities of the polycyclic aromatic chemical benzo-a-pyrene in the whales and that this chemical was emitted as a waste by Alcan Aluminium Inc. plants along the Saguenay River. A company spokesman said such a direct link had not been conclusively proved.

Dr. Beland also noted that the autopsies found lesions of kinds never before encountered in marine mammals, as well tumors in numbers 10 times as great as normally found.

He reported that many belugas were dying starting at the age of 14 or 15, whereas a healthy whale can live 30 years. Even more ominous for the future of the St. Lawrence belugas is his estimate that the ratio of young to adult belugas has sunk below what is required for the population to expand. Report on Brain Tissues