The Saguenay–St. Lawrence Marine Park: oceanographic processes at the basis of this unique forage site of northwest Atlantic whales
The results from an ecosystem research program are summarized. It was conducted in the Saguenay–St. Lawrence Marine Park to understand the basic processes responsible for the existence of this traditional whale feeding ground, discovered by the Basques whalers 450 years ago. Persistent processes maintain aggregated whale preys at the head of the main deep-water channel of eastern Canada continental shelf. What are they? This site is the richest krill aggregation yet documented in the northwest Atlantic. The mechanisms responsible are the pumping, retention and concentration of adult krill from the Gulf of St. Lawrence, by the strong estuarine circulation of the St. Lawrence. Tidal currents upwelling along channels and bank slopes combine with adult krill vertical behavior and concentrate it. This process is more intense at the head of the channels where tidal upwelling is amplified. It is locally enhanced by wind-driven coastal upwelling. The mean circulation transports the rich krill patches along the slopes of the basins. At the mouth of the estuary, the concentrated krill at the margin of the large cyclonic Anticosti gyre (counterclockwise) is injected into the lower estuary on the northern side, under favorable circulation conditions. The narrow slope current flowing upstream along the estuary then imports it towards the Marine Park krill aggregation zone. Pelagic forage fish such as capelin also aggregate at the channel head and entrance of the fjord under the action of the tidal upwelling currents and fronts, which also concentrate and enhance the availability of their preys. They contribute to the feeding of whales and sea birds. Special oceanographic features, seldom found elsewhere, combine in the Marine Park to generate this whale feeding ground. Anthropogenic pressures and climate change are the main threats to its preservation for the next centuries.