Blue Whales, Balaenoptera musculu, are one of few animals in the world that can truly be described as unique.  These beautiful marine mammals grow up to 100 feet (30 meters) in length and can weigh in excess of 150 tons.  They are the largest animals ever known to have lived on earth.  And yet it is truly inspiring to see how graceful and beautiful these creatures are as they swim swiftly through almost all oceans on our planet.

Blue Whale, Balaenoptera musculus, Dana Point, California (Steven W Smeltzer)Once numbering in the hundreds of thousands and living in all oceans, these amazing animals were  hunted almost to extinction until the Convention on Fishing and Conservation of Living Resources on the High Seas was signed in 1966.  At that time the number of Blue Whales was estimated to be around 1,000.  Today the estimated population of Blue Whales is around 4,500 to 5,000, with the population growing at about 8% per year.  The Blue Whale is an endangered species, but the growth rates over the last 10 to 15 years are encouraging and it demonstrates the value of coordinated conservation on a global basis.

Blue Whales

blue whale

The Blue Whale is very long and slender with various shades of bluish-grey on the top or dorsal side and somewhat lighter underneath. There are three known and distinct subspecies: B. m. brevicauda (also known as the pygmy blue whale) found in the Indian Ocean and South Pacific Ocean, B. m. musculus of the North Atlantic and North Pacific and B. m. intermedia of the Southern Ocean . B. m. indica, found in the Indian Ocean, may be another subspecies.

The diet of the blue whale is almost exclusively small crustaceans (krill).  The blue whale may in fact consume up to 40 million or 3,600 kg of krill on a daily basis.  It eats by expanding its throat plates and takes in enormous amounts of water which also contains krill and then pushes the water out through its baleen plates and swallows the krill.  Blue Whale, Balaenoptera musculus, Dana Point, California (Steven W Smeltzer)

The blue whale is found alone or in small groups in all oceans, but populations in the Southern Hemisphere are much larger. In the Northern Hemisphere, blue whales can be seen regularly in the Gulf of St. Lawrence and off the coasts of Monterey, California, and Baja California, Mexico.  The blue whales migrate to the colder waters near the poles in the summer to feed and migrates back to equatorial regions to breed in the winter.

References:

Branch TA, et al. 2004. Evidence for increases in Antarctic blue whales based on Bayesian modelling. Mar Mamm Sci 20:726-754.

Branch TA, et al. 2007. Past and present distribution, densities and movements of blue whales Balaenoptera musculus in the Southern Hemisphere and northern Indian Ocean. Mamm Rev 37:116-175.

Calambokidis J et al. 2009. Insights into the population structure of blue whales in the eastern North Pacific from recent sightings and photographic identifications. Mar Mamm Sci 25:816-832.

Calambokidis, J et al. 2008. Insights into the underwater diving, feeding, and calling behavior of blue whales from a suction-cup attached video-imaging tag (CRITTERCAM). Mar Tech Soc J 41:19-29.

Calambokidis, J et al. 1990. Sightings and movements of blue whales off central California 1986-1988 from photo-identification of individuals. Rep Int Whal Commn (Special Issue 12): 343-348.

Croll DA et al. 1998. An integrated approach to the foraging ecology of marine birds and mammals. Deep-sea Res II 45: 1353–1371.

Cummings WC and Thompson PO. 1971. Underwater sounds from the blue whale, Balaenoptera musculus. J Acoust Soc Am 50:1193-1198.

Fiedler PC et al. 1998. Blue whale habitat and prey in the California Channel Islands. Deep-sea Res II 45: 1781–1801.

Gill PC. 2002. A blue whale (Balaenoptera musculus) feeding ground in a southern Australia coastal upwelling zone. J Cet Res Manage 4:179-184.

Gilpatrick JW, and WL Perryman. 2008. Geographic variation in external morphology of North Pacific and Southern Hemisphere blue whales (Balaenoptera musculus). J Cet Res Manage 10:9-21.

Leduc RG, et al. 2007. Patterns of genetic variation in southern hemisphere blue whales, and the use of assignment test to detect mixing on the feeding grounds. J Cet Res Manage 9:73-80.

McDonald MA, et al. 2006. Biogeographic characterisation of blue whale song worldwide: using song to identify populations. J Cet Res Manage 8:55-65.