What influences the accumulation of whale food in the Estuary?
Situated between Tadoussac and Les Bergeronnes, the head of the Laurentian Channel is one of the major plankton traps of the North Atlantic. Several species of whales come to feed in this area over the course of the summer. What factors influence these accumulations of whale food?
To go through the looking glass
Researchers use active acoustic techniques to locate schools of capelin and krill. By comparing echoes at several different frequencies, researchers can classify them by organism type. Samples are also harvested using plankton nets and trawlers to validate what is detected using acoustic techniques.
Krill can usually be found over deep basins at depths of between 50 m and 150 m, which corresponds to the cold intermediate layer of the Estuary. Plankton net samples have demonstrated that the most abundant species at the head of the Laurentian Channel is the cold-water krill species Thysanoessa raschi. Further, only mature 2-year-old representatives of this species are present in this area. Clouds of krill can occasionally be observed near the surface, particularly at night. This phenomenon can be explained by various oceanographic factors and behaviours such as the vertical nocturnal migration of krill, the cold-water upwelling at the head of the Laurentian Channel, currents and predator evasion. High krill concentration zones correspond to the areas of high blue whale concentration zones, as identified by Richard Sears. Huge quantities of krill—as much as 100 000 t—have been detected at the head of the Laurentian Channel. Capelin appears to avoid the cold intermediate layer, swimming either above it or below it. The largest schools of capelin can be found over reefs along the periphery of the Channel.
Yvan Simard, Maurice-Lamontagne Institute (MLI) and Director of the Fisheries and 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), Cédric Côté, ISMER, Diane Lavoie, MLI, François Saucier, MLI and Director of the Fisheries and Oceans Canada research chair in regional ocean climate modelling at ISMER-UQAR, Nathalie Roy, MLI, Marc Sourisseau, post-doctoral researcher at MLI and ISMER.
Simard, Y., D. Marcotte, and K. Naraghi. 2003. Three-dimensional acoustic mapping and simulation of krill distribution in the Saguenay—St. Lawrence Marine Park whale feeding ground. Aquat. Living Res. 16(3): 137-144.
Simard, Y., Lavoie, D., and Saucier, F.J. 2002. From plankton to whales: Oceanography of a traditional whale feeding ground and marine park in the St. Lawrence Estuary. ICES CM 2002/N:14.
Simard, Y., D. Lavoie, and F.J. Saucier. 2002. Channel head dynamics: Capelin (Mallotus villosus) aggregation in the tidally-driven upwelling system of the Saguenay—St. Lawrence Marine Park’s whale feeding ground. Can. J. Fish. Aquat. Sci. 59: 197-210.
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Marchand, C., Y. Simard, and Y. Gratton. 1999. Concentration of capelin in tidal upwelling fronts at the head of the Laurentian Channel in the St. Lawrence Estuary. Can. J. Fish. Aquat. Sci. 56: 1832-1848.
Simard, Y., and D. Lavoie. 1999. The rich krill aggregation of the Saguenay—St. Lawrence Marine Park: hydroacoustic and geostatistical biomass estimates, structure, variability and significance for whales. Can. J. Fish. Aquat. Sci. 56: 1182-1197.
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