Tides – generally two high and two low per day – generate and influence ocean currents. In turn, these currents act directly and indirectly on the movements and distribution of whales.
For the belugas that ply the Saguenay Fjord, these cyclical movements serve as a travelling route up and down the river, from Baie Sainte-Marguerite to the mouth of the Fjord. Taking advantage of the natural phenomenon of the rising tide, they travel up the Fjord while reducing their energy expenditure. Occasionally, they can also be observed swimming against the current, perhaps to better hunt prey coming from the opposite direction.
These tidal currents influence the distribution of fish and plankton preyed upon by cetaceans. Whales frequent the St. Lawrence River primarily to feed. Thus, their movements and their concentration depend on the presence of their prey. At high tide, capelin converge in large schools prized by baleen whales. Several of the latter then gather around their prey to feed. For example, in the St. Lawrence Estuary, fin whales that feed on capelin are more often observed at high tide and during the day.
Like the tide, wind, underwater topography, climatic conditions and the behaviour of their prey have an influence on whales’ distribution. Krill, the primary prey of blue whales, tend to form huge concentrations near the surface during the night, which is when these giants frequently feed.
In sum, although tides do indirectly influence the movement of cetaceans, we cannot rely solely on this variable to plan our whale-watching cruises.