From plankton to whales: Oceanography of a traditional whale feeding ground and marine park in the St. Lawrence estuary

No abstracts are to be cited without prior reference to the author.

The head of the main channel of the eastern Canadian continental shelf is a traditional whale feeding ground that is part of the first Canadian marine park and one of the most intensive whale-watching sites in the world. In mid 1990's, a research program was launched to understand the basic oceanographic processes responsible for this ecosystem hot spot of eastern Canada. Multifrequency acoustics, direct sampling and standard oceanographic measurements were used to map the distribution and abundance of the two whale preys, krill and capelin. Data were interpreted with the help of a high-resolution three-dimensional tidal circulation model of the area. The area was found to be the site of the richest krill aggregation in the Northwest Atlantic. It results from the pumping of waters from the krill-rich intermediate layer by the estuarine circulation and intensive upwelling combined with the negative phototactism of krill. Current structure and hydrodynamic control at the sills determine the mesoscale pattern of the aggregation. Capelin concentrated at the channel head banks and along the slopes. Flooding currents and upwelling were concentrating them at the slopes, and along the fronts that form at the interfaces between water masses. Flooding increased the contact between the two preys. Whales take advantage of the cyclical concentration of capelin at the slopes and of the richest krill concentrations further downstream.