by Piter Kehoma Boll
I think most of us know already that the largest animal ever is our beloved blue whale, Balaenoptera musculus. It can reach 30 m in length and weigh more than 180 tonnes. It’s really big, but probably not as big as many people think. There are some popular legends, like that the heart of a blue whale is the saze of a car or that a human could swim inside its aorta, which are not actually true.
But what else can we say about the blue whale? It is a rorqual, a name used to designate whales in the family Balaenopteridae and, as all of them, its main and almost exclusive food is krill, a small crustacean very abundant in all oceans. And krill needs to be abundant in order to provide the thousands of tonnes that all whales in the oceans need to eat every day. A single blue whale eats up to 40 million krill in a day, which equals to roughly 3.5 tonnes. A blue whale calf (young) is born measuring around 7 m in length and drinks around 500 liters of milk per day!
Blue whales were abundant in nearly all oceans until the beginning of the 20th century, when they started to be hunted and were almost extinct. Nowadays, the real population size is hard to estimate, but may encompass as few as 5,000 specimens, much less than the estimated hundreds of thousands in the 19th century. Due to such a drastic reduction in the population, the blue whale is currently listed as “endangered” in IUCN’s Red List.
Occasionally, blue whales can hybridize with fin whales (Balaenoptera physalus) and perhaps even with humpback whales (Megaptera novaeangliae), a species classified in a different genus! Some recent genetic analyses, however, indicate that the Balaenoptera genus is polyphyletic and the blue whale may become known as Rorqualus musculus.
Different from other whales, blue whales usually live alone or in pairs, but never form groups, even though they may sometimes gather in places with high concentrations of food.
Like other cetaceans, especially other baleen whales, the blue whale sings. The song, however, is not as complex and dynamic as the ones produced by the related humpback whale. An intriguing fact that was recently discovered is that the frequency of the blue whale song is getting lower and lower at least since the 1960s. There is no good hypothesis to explain this phenomenon yet, but several ones have been proposed, such as the increase in background noise due to human activities or the increase in population density due to the decrease in whaling.
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Hassanin, A.; Delsuc, F.; Ropiquet, A.; Hammer, C.; van Vuuren, B. J.; Matthee, C.; Ruiz-Garcia, M.; Catzeflis, F.; Areskoug, V.; Nguyen, T. T.; Couloux, A. 2012. Patter and timing of diversification of Cetartiodactyla (Mammalia, Laurasiatheria), as revealed by a comprehensive analysis of mitochondrial genomes. Comptes Rendus Biologies, 335: 32-50.
Mellinger, D. K.; Clark, C. W. 2003. Blue whale (Balaenoptera musculus) sounds from the North Atlantic. Journal of the Acoustical Society of America, 114(2): 1108-1119.
Wikipedia. Blue whale. Available at: <https://en.wikipedia.org/wiki/Blue_whale>. Access on January 27, 2016.