How do they find their way?

By following the stars? By relying on prevailing currents? By detecting variations in the Earth’s magnetic field? Possibly. It is believed that large rorquals use very low frequency sounds similar to sonar to detect underwater reliefs, and that they are able to retain these “acoustic maps” in their memories. Baleen whales are also believed to have the ability to “taste” differences in the composition of water masses, and thereby to find their way back to the mouth of a river or the edge of the sea ice. Despite numerous discoveries, to date no single theory can explain this remarkable accuracy that whales have to navigate their way through the oceans.

Two sei whales

Where do the giants of the St. Lawrence go?

It all depends on the species. Humpback whales of the Northwest Atlantic gather in the Caribbean in the winter, then disperse in summer to different feeding areas including the Gulf of Maine, the coasts of Newfoundland or the St. Lawrence. A US study based on the detection of fin whale vocalizations has shown that this species is found throughout the North Atlantic year round. The study also revealed a gradual northward movement of animals in the spring and southward in the fall, though no large congregations. With regard to blue whales, “acoustic spying” has revealed their presence from the Grand Banks of Newfoundland to Bermuda. Other individuals have also been spotted in the St. Lawrence in the middle of winter, risking their lives to feed amongst the ice floes.

Researchers have observed that Pacific blue whales return to the same places every year and on similar dates. Curiously, their feeding grounds are not necessarily the most productive areas. Rather, they are the most predictable ones. By favouring stability over quantity, blue whales avoid unpleasant surprises in a highly variable ecosystem. Blue whales are able to benefit from this strategy because they have a life expectancy of 80 years, which allows for long-term learning.

How are whales tracked when they migrate?

Thanks to satellite telemetry, whale movement and activity can be monitored over great distances and long periods, thereby revealing multiple aspects of their journey: routes taken, nursing breaks, travel speed, etc. This technology suggests that the Azores are a genuine springtime “oasis” for fin and blue whales heading toward Greenland; and the cruising speed of these great cetaceans is thought to vary throughout the day and according to the geographic regions through which they are passing. These variations are thought to be attributable to the diurnal cycle, which influences the depth at which their prey congregate as a function of light levels.

Analysis of baleen samples from whale carcasses also can be used to learn more about an individual’s movements during the last years of its life. In the late 1980s, scientists discovered that certain events in a whale’s life leave biochemical traces in its baleen. The farther away from the gum, the longer ago the event occurred. By comparing the ratios of stable isotopes in baleen and in the oceans, an individual’s movements can be determined as far back as 25 years for right and bowhead whales and 5 years for blue and fin whales.