Species Profiles: blue whale
ContentsClassificationClass: Mammalia
Order: Cetecea Suborder: Mysticeti Family: Balaenopteridae Genus: Balaenoptera Species: musculus Common names: Blue Whale, Sulphur Bottom Irish Name: Míol mór gorm. top Key Identification FeaturesMax. adult body length/weight: 31-33m / 178,000kg
Average adult body length/weight: 25m / 80,000 - 130,000kg Average length/weight of calf at birth: 7m / 2,500 – 4,000kg Blow: Very strong blow, rising in a single thick column, 6-12m into the air. Head: Forms less than a quarter of total length. Broad, flattened rostrum forming a U-shape. A single raised ridge runs from almost the tip of the rostrum to the splash-guard around the blowhole. This splashguard is very prominent. Dorsal Fin: Tiny, low triangular fin. About 30cm high, set three quarters of the way back along the body (may not be visible from a distance). Colouration: Blue-grey, mottled with grey, white or silvery patches. Flipper tips and undersides lighter. The blue colour varies among individuals but may also darken with age. Markings: Some individuals, particularly in the North Pacific may obtain yellow undersides through marine diatoms growing on their skin. top Field IdentificationBlue whales break the surface with a massive blow about 10 metres high. The rostrum (the
flat area in front of the splash guards) is flat and rarely breaks the surface. The enormous splash- guards protrude high out of the water. Dorsal fins are not always visible on surfacing, as some individuals are so long that they are below the surface by the time the dorsal fin passes. The region behind the head is extraordinarily wide and the spine appears like a massive muscular column down a broad rotund back. Their sleek bodies may give rise to under-estimation of their huge size. Tail flukes are wide and triangular, with a slight notch in the centre. A smaller form of the blue whale exists. The pygmy blue whale (B. m. brevicauda) is generally under 22m in length, with a shorter tail region, shorter baleen plates and a different skull anatomy. top Species Similar in AppearanceMay be confused with any of the other large baleen whales but there are noticeable differences in the blow, surfacing sequence and appearance of the flukes (see relevant species profiles for details). The major risk of confusion is between fin and blue whales. Important differences are: · Shape of the rostrum:§ Fin: V-Shaped. § Blue: U-Shaped. · Surfacing sequence: § Fin: Blow followed shortly after by the dorsal fin. § Blue: Blow followed by a tiny dorsal fin after a long roll. · Roll and flukes:§ Fin: Rolls high out of water. Does not show flukes. § Blue: Rolls lower in the water and occasionally flukes before a deep dive. top Status and DistributionThe population is still recovering from the slaughter of 30,000 whales during the height of the Antarctic whaling industry. They are found in oceans worldwide but feed only in the colder waters of the Antarctic, North Pacific and North Atlantic. They are generally found in deep waters along the edge of continental shelves. The northern and southern hemisphere populations are distinct with little migration between populations. They are separated temporally while in tropical waters. The North Atlantic population moves south in winter towards their breeding areas near the equator. Numbers in the North Atlantic may be as low as 400 individuals. The range of the pygmy blue whale is narrower and they do not migrate as far into the polar region. A year-round population exists off the Californian coast. There may be fewer than 1,000 pygmy blue whales alive and were hunted by the Russians up until 1972. top Reproduction and Life CycleMax. life expectancy:80+
Average life expectancy: at least 30+ Mating Occurs: Summer. Season of birth: Winter. Gestation: 11-12 months. top Conservation IssuesThe discovery of blue whales passing the west coast each winter may mark a slow recovery in the blue whale in Irish waters. Numbers in the North Atlantic may still be as low as 400 individuals. The only significant threat in Irish waters is noise pollution from offshore exploration and drilling along the West Coast. As with most creatures which use low-frequency sound for communication, they are sensitive to acoustic disturbance. top |
 Where and When Best Seen in IrelandOnce relatively common in Irish waters, 98 animals were landed between 1908-1914 and 27 between 1920-1922 at the Blacksod Whaling Station in Co. Mayo. Although much rarer now, there have been a number of sighting off the Irish west coast in recent years. Research using US Navy underwater recording equipment has detected blue whale mating calls off the west and north-west coasts indicates that an estimated 30-50 may pass through Irish waters each year. A single animal was sighted by researchers in UCC in the Rockall Trough in 2001. More recently two animals were photographed by IWDG staff and members feeding among fin whales along the shelf slopes, off the west coast in September 2008. top Stranded AnimalsFlippers are relatively short (less than 10% of body length) and tapered at the ends. 55-95 throat grooves, extending for about 60% of the body length. The baleen is all black (though may be greyer in old animals), unlike the fin whale’s which is yellow and slate coloured baleen, with white baleen at the front, right side of the mouth. 270-400 black baleen plates on each side of the upper jaw. Blue whales have a rudimentary moustache of 4 bristles and an adolescent beard of ~40 hairs. 63-64 free vertebrae. Blue whales have the largest penis of any animal, measuring in at 3m. top BehaviourThey swim at 3-4knots but can accelerate to 10-16knots. Blow every 10-20 seconds for 2-6 minutes and dives for 5-20 minutes. Adults rarely if ever breach but calves have been observed breaching. Although they do not always fluke (lift tail flukes) on diving, they will occasionally do so on the last (terminal) dive of a sequence. Any large baleen whale observed fluking in Irish waters could be a blue whale but is more likely to be a humpback. Blue whales emit low frequency moans (1-3Hz) that can travel for great distances underwater. They also produce ultra-sonic bursts of sound (21-31kHz) when feeding; this may help them detect large concentrations of krill. top Food and FeedingFeed on swarming planktonic crustacea or krill (almost exclusively on a few species such as T. longicornis and M. norvegica). Blue whale may swallow 4 tons of such food per day. top Social StructureFound either singly or in close-knit groups of 3-4 animals but may form larger groups for feeding and breeding. top |