A Natural Food Storehouse for Whales - The Result of a Fragile and Unique Ocean Equilibrium

Located at the junction of the Quebec City, Saguenay–Lac-Saint-Jean and North Shore regions, the Saguenay–St. Lawrence Marine Park is the site of a rich feeding ground for whales, both summer residents from the Atlantic and belugas that live there year-round. The unusual topography of the ocean bottom provides favourable conditions for concentrations of organisms and small fish that provide food for marine mammals. This phenomenon has attracted whales to the area for centuries, stretching back to when Basque whalers hunted them some 450 years ago. It is a subject of particular interest to Yvan Simard, a researcher at Quebec's Maurice Lamontagne Institute. Under St. Lawrence Vision 2000, a federal-provincial research program implemented in the 1990s, Mr. Simard studied the processes responsible for the existence of this natural food storehouse, using tools that included multi-frequency hydroacoustic equipment and oceanographic techniques.

The Saguenay–St. Lawrence Marine Park is the point farthest upstream on the continent where large migratory whales can be observed. In the spring, whales arrive from far away in the Atlantic Ocean, where they had migrated the previous fall to breed or escape the ice cover that forms in the St. Lawrence Estuary. When the ice breaks up in the spring, the whales undertake the long return journey, passing through the Strait of Belle Isle and Cabot Strait. They can thus benefit from the rich abundance of food in the estuary by stopping over in a number of feeding grounds to build up their fat reserves, which are crucial to their reproductive success. The feeding ground in the Saguenay–St. Lawrence Marine Park has some special characteristics rarely seen elsewhere, which relate to the distinctive ocean bottom topography and the currents in the St. Lawrence Estuary.

A long underwater valley called the Laurentian Channel extends from the mouth of the Saguenay (near Tadoussac) to a point between Nova Scotia and Newfoundland. This 300 to 500 metre deep trough stretches more than 1,000 kilometres, from the maritime estuary and the Gulf to the entrance of the Atlantic Ocean. The channel is characterized by the presence of two marine currents: a surface-layer current, which transports low-density freshwater flows in a downstream direction and a deep-layer current, which transports salt water from the Atlantic Ocean to the head of the channel in the St. Lawrence Estuary. (See image opposite)

Krill, small crustaceans that are an important food source for whales, are carried in the cold waters that flow in from the ocean. Resembling shrimp,  krill swim in a depth interval of 75 to 150 metres during the day to escape predators and come back to the surface at night to feed. Carried by the deep water current moving upstream in the underwater trough, the krill finish their journey at the head of the channel, which forms a cul-de-sac at Tadoussac. This underwater wall, the terminus of the underwater trough, stops the current and forces cold waters back up to the surface under the powerful action of the tides. The krill are thus brought to the surface;  they swim towards the bottom, struggling against the rising current. These descending krill mix with the swarms of krill rising from the bottom, forming a dense layer upon which whales come to feed. This large concentration of krill attracts other predators as well, including capelin, a favourite food for whale species such as minke whales and belugas.

This large concentration of food—the spectacular result of a combination of physical and biological phenomena—is closely tied to climatic conditions. Indeed, the circulation of water in the estuary,  characterized by two-layer marine currents, is dependent on freshwater inflows from the St. Lawrence as well as on other factors. Water temperatures also influence the size of krill aggregations in ocean waters. Climate change may thus have a predictable impact on the entire system. Although difficult to predict, over the long term, climate change is bound to affect many of the marine species in this food chain. At present, owing to financial constraints, no government agencies or private research facilities have the data collection capability to monitor the whale populations that are present in the vast expanse of the Gulf of St. Lawrence.

Studies are being carried out to document other factors that could disturb this natural food storehouse, such as the impact of noise on whales. These animals use sounds extensively to communicate with one another, locate prey and navigate underwater. Beluga whales are so highly vocal that they have been nicknamed “sea canaries” due to the squeals and chirps they make. Sound, particularly the frequencies used by whales, travels faster and much farther in water than in air. A whale's call can be heard by another whale 100 kilometres away. Noise introduced into this communication system will thus interfere with it. However, the Saguenay–St. Lawrence Marine Park is home to one of the only whale feeding grounds that is located in the middle of a major shipping channel, used by ships transporting cargo between the Great Lakes and the Atlantic Ocean and vice-versa. Each ship emits a noise field measuring 20 kilometres in diameter. Therefore, when a number of vessels are sailing at the same time, the entire area is saturated with noise. For marine animals that communicate acoustically, the situation can be likened to a room full of people talking in loud voices: two people standing together can understand each other but they cannot communicate with someone on the other side of the room. Yvan Simard's research is thus focused on measuring the noise levels in the area as well as on assessing the impact of commercial ships and ecotourism vessels on whales' acoustic environment in the Saguenay–St. Lawrence Marine Park.