This decline probably began as long ago as 1700. Today the numbers continue to fall as a result of a combination of factors so varied that this single population of belugas can be said to have suffered from the effects of virtually every human activity that threatens other small cetaceans around the world.
Most of the initial damage was caused, over a period of 250 years, by a large commercial hunt, conducted by the first Europeans and then by Canadians, who killed the whales for their blubber and oil. By the time this hunt ended in the 1950s, as a result of a decline in the market for whale oil, the beluga population had fallen to less than 2,500.
Belugas had meanwhile become scapegoats for periodic failures in the St Lawrence fisheries. In the late 1920s, the Quebec government argued that it was necessary to kill them in order to protect fish stocks and a cull was instituted with hunters being paid a bounty for each whale they killed.
During the 1950s, the St Lawrence River area underwent major industrial development with the increased growth of cities like Montreal and Quebec City, the establishment of international shipping ports and the construction of the St Lawrence Seaway, which opened up an important route for shipping from the Great Lakes to the Atlantic. This resulted in an increase in the amount of wastes and pollution reaching the river and a tremendous rise in the level of boat traffic in the region.
In addition, the construction of dams on rivers such as the Manicouagan, Outardes and Bersimis, all of which flow into the St Lawrence, may have critically altered important beluga habitats; the range of these animals is now believed to be about half the area it was 50 years ago.