Migrationpar Robert Michaud, Martine Bérubé et Janie Giard, du GREMM But why migrate?There are as many answers to this question as there are migratory species. Often, animals migrate in search of high-density feeding grounds. This may be the case for bowhead whales who summer in the Arctic. Migration can also be motivated by reproductive strategy. There’s no question that this is what prompts humpback whales to gather in Caribbean waters in the winter. These great gatherings possibly facilitate encounters between males and females. The fact that fin whales and blue whales do not hold such gatherings in the winter raises some fascinating questions. It is possible that the very low frequency sounds emitted by these two species enable males and females to locate each other, even if they are dispersed across the Atlantic. According to officials with the U.S. Navy’s underwater espionage network, blue whales emit infrasonic sounds with frequencies as low as 17 hertz, for 16 seconds on average, which can be heard several hundred kilometres away! Where do the giants go?Every summer, Grand Galop and a few dozen other fin whales come to feed off Tadoussac. Others, like Peanut and Curley, are "regulars" in the Jacques-Cartier Strait around Mingan. The fin whales of the Gulf of Maine, the Bay of Fundy and elsewhere in the North Atlantic demonstrate the same "site fidelity" to their summer feeding grounds. This information is the fruit of a vast campaign undertaken by researchers on both sides of the Atlantic to "track" these animals. In order to monitor the comings and goings of several whale species, scientists use photo-identification, a technique whereby natural markings, scars or dorsal fins are photographed in order to identify individual whales. In the St. Lawrence, researchers at the Mingan Island Cetacean Study (MICS) and Le Groupe de Recherche et …ducation sur les MammifËres Marins (GREMM ) have used this technique to develop individual observation records on several hundred whales. Among other things, these records have revealed that the blue whale is more nomadic than the fin whale, visiting the St. Lawrence less regularly and for shorter periods of time. In all likelihood, the blue whale adapts its travel itinerary to fluctuations in the abundance of krill, its food source. According to Richard Sears, of the MICS, less than one quarter of the 350 blue whales photographed in the St. Lawrence return regularly. So where do the others go? Despite growing efforts to observe whales elsewhere in the North Atlantic, only a few dozen blue whales have been photographed outside of the St. Lawrence. And only a very small number have been photographed in both bodies of water. Via Lactea, first observed in the St. Lawrence in 1984, was later photographed off Greenland in 1988 and 1989. Since then, he has been seen regularly in the St. Lawrence. These observations represent the first pieces in a puzzle researchers are working hard to solve. Tracking by way of photo-identification has enabled researchers to describe the migratory habits of the humpback whale. As is the case with fin whales, North Atlantic humpback whales spread out in the summer, travelling to several feeding areas to which they return fairly faithfully. In the fall, they leave their feeding grounds and undertake an impressive journey — some travelling as far as 5000 kilometres — to return to the temperate and protected waters of the Caribbean, where they congregate for the winter. Researchers are drawn to this gathering place around the Dominican Republic and Puerto Rico where they continue the work they started farther north. Most of the large whales whose migratory patterns are well documented follow the humpback whale model. During the summer, they feed in the rich waters found at higher latitudes and then spend the winter in tropical and subtropical waters. No comparable gathering seems to take place among fin whales and blue whales in the North Atlantic. Until recently, the migratory habits of the two largest animals on Earth were a well-kept secret. A unique research program, however, has shed new light on the topic. Chris Clark, from the bio-acoustical laboratory at Cornell University, was invited in the early 1990s to join a team of scientists with the United States Navy which had used hydrophones to detect submarines and other ships. Before dismantling this system, which has become obsolete with the advent of more discreet nuclear-powered submarines, the Navy made this equipment available to Clark. Recordings obtained in this fashion enabled him to detect the presence of fin whales in the North Atlantic year round. He was also able to discern the gradual northward movement of these animals in the spring and their movement south in the fall, but there was never a concentration of sonar activity in a single place. These recordings corroborate the very first scientific hypotheses formulated at the turn of the century by R. Kellogg. In 1929, this researcher analyzed hunting statistics and hypothesized the existence of several distinct populations of fin whales in the North Atlantic. Genetic analyses recently conducted by Martine BÈrubÈ of the Cetacean Genetic Group, using skin samples from fin whales from six different feeding grounds in the North Atlantic and the Mediterranean, confirmed this hypothesis. It appears that distinct populations of fin whales migrate short distances in the Atlantic but never gather in a single area. In the summer, one population will establish itself in a region, occupied in the winter by another, which itself migrates farther north in the summer to feed. Despite these significant findings, we still have no idea where Grand Galop goes for the winter!
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