Question of the monthDuring an interview with Yvan Simard, Researcher at the Maurice Lamontagne Institute and Fisheries and holder of Oceans Canada chair in applied marine acoustics for research into resources and the ecosystem at the Institut des sciences de la mer (ISMER) based at the Université du Québec à Rimouski (UQAR) , Whales on-line asked him the following question: Is the St. Lawrence an exceptionally rich area for whale food?Y. S. : The richest known aggregation of krill in all of the Northwest Atlantic lies within the confines of the Saguenay—St. Lawrence Marine Park. During a survey carried out over the summer of 1994, we evaluated that there were some 100 000 t of krill in a relatively small zone at the head of the Laurentian Channel. This remarkable amount indicates that krill is present in very high concentrations in this area, which makes it exceptionally interesting for whales who come here to feed. If this krill were dispersed throughout the entire Gulf of St. Lawrence, whales would have to filter such a large volume of water that they would soon tire themselves out. The core of this aggregation of small crustaceans known as krill—baleen whale food—is situated between Les Escoumins and Cap-de-Bon-Désir. Capelin is also abundant in this area; capelin feeds on krill and is also a prey species of whales. What causes these krill aggregations? Deepwater currents that flow up the St. Lawrence Estuary carry krill concentrations with them from the Gulf of St. Lawrence. These concentrations are then trapped in the cul-de-sac at the head of the Laurentian Channel that is situated between Tadoussac and Les Escoumins. Here, krill become even more concentrated under the influence of tide currents, making it even easier for whales to feed. This explains why this portion of the St. Lawrence attracts whales that have been coming here to feed for centuries. Are there other major accumulation zones in the St. Lawrence? There are other zones in the St. Lawrence favourable to the accumulation of zooplankton and other animal organisms. Moreover, these are areas where several species of marine mammals go to feed in the summer months. Dominant west winds drive surface water offshore along the north shore of the Gulf, provoking an upwelling of cold, deep waters along the coast. These waters bear krill, which then adhere to the edge of the Channel. Another accumulation zone is formed at the tip of the Gaspé Peninsula. The mechanism that influences this zone is still poorly understood, but it is presently being studied. Finally, there is the Anticosti gyration, a counter clockwise revolving current situated at the western tip of the Island at the entrance to the Estuary. This current is an “oceanographic structure” that plays an important role in the production and retention of krill and capelin within the St. Lawrence. |