Saguenay Fjord

A fjord is a valley carved by glacial erosion and then flooded by the sea. At the end of the Wisconsin glaciation 10,000 years ago, a glacier retreated and eroded a pre-existing fault. The 2-kilometre wide valley was then flooded by water from the St. Lawrence Estuary, unlike most fjords, which flow directly into the ocean. This is how the Saguenay Fjord and its 500-metre high cliffs were formed.

The 105 km long fjord begins at Saint-Fulgence and ends in Tadoussac, where the Saguenay River spills into the St. Lawrence. At Tadoussac, the Fjord is narrower and shallower. This is because during deglaciation, the glacier began to float atop the river water in these parts, effectively ending any erosion.

Confluence of the Saguenay and the St. Lawrence

The waters of the Saguenay and St. Lawrence have very different properties. In the Saguenay, the water is less saline, warmer and rich in tannins, which explains its brownish colour. In the St. Lawrence, the water is saltier, colder, and richer in microscopic algae, which explains its greenish hue. Phytoplankton is at the base of the food chain: it allows for the proliferation of zooplankton which, in turn, provides food for fish. Depending on the species, whales feed on fish or directly on zooplankton.

These waters are thus of different densities and do not mix, a bit like oil and water. As a result, when the waters of the Saguenay meet those of the St. Lawrence, a front is formed which shifts with the tides. During a rising tide, the waters of the St. Lawrence push back those of the Saguenay. The front thus shifts toward the Saguenay, carrying nutrients with it. During an ebb tide it is the opposite, as the strip of water of the Saguenay, called the plume, edges toward the St. Lawrence. The effects of the tides are visible as far as Chicoutimi, which marks the beginning of the Fjord.

Tides therefore modify the water composition at the mouth of the Saguenay and throughout the Fjord, which has an impact on fish and plankton distribution. Whales therefore adjust their behaviour to feed more effectively.

Minke whales

Certain individuals frequent the Saguenay up to 10 or so nautical miles upriver. The different properties of the Saguenay sector and the head of the Laurentian Channel are the underlying reason for the different feeding strategies used by minke whales. In the Saguenay, this species spends much more time gathering its prey near the surface. In the Laurentian Channel, upwelling might do some of the work for them by forcing their prey to the surface. In these conditions, minke whales probably do not need to perform as many prey-gathering manoeuvres.

Belugas

Belugas can be seen in the Saguenay as far upriver as Île Saint-Louis, not far from Baie Sainte-Marguerite. It is usually females accompanied by their calves that go there. Belugas take advantage of the rising tide phenomenon to swim upriver, thereby reducing their energy expenditure.

Seals

Harbour seals are year-round residents of the St. Lawrence. In the Saguenay Fjord, there are haulout sites near Cap Éternité and Cap Fraternité. It is at these rocky places that seals come out of the water to rest, moult or reproduce.

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