A 6 ton model, and a baby that puts on 90 kg a day: rorquals part I
I’ve said it before but it’s worth saying again: everyone interested in animals is, I assume, fascinated by whales. All secondarily aquatic tetrapods are neat, but here we have a group that has evolved giant size, suspension feeding, macropredation, deep-diving and echolocation, among other things. Right now, I have rorquals on my mind, and I’m not quite sure why: I haven’t been doing any research on them lately, nor have they been in the news or anything*. However, later this week my family and I are visiting the Natural History Museum (London) and I’m particularly looking forward to showing Will (who’s 5) the life-sized Blue whale Balaenoptera musculus model that hangs in the Mammal Hall (the room formerly known as the Whale Hall). I’m so interested in this model that I feel it worthy of a short digression.
* Bar the news that
Late in the 1920s plans to replace the old whale hall of the
Scaling up from a clay model, a wooden frame was constructed, and this was then covered in wire mesh and plaster. A trapdoor on the stomach was constructed for (I presume) internal maintenance, though apparently the workmen would sneak inside the model for secret smoking. On several occasions I’ve heard rumours that a time capsule was left inside this trapdoor before it was sealed: Stearn (1981) made no mention of this specifically, but did write that a telephone directory and some coins were left inside (p. 132). The completed model weighed between 6 and 7 tons and, when the time came for the whale to be painted, Stammwitz and Fraser disagreed, eventually choosing bluish steel-grey. Completed in December 1938, it was the largest whale model ever constructed though larger models, constructed from the same design templates, have since been produced by several American museums [adjacent image from here].
What are rorquals? They are the eight or so Balaenoptera species of the mysticete family Balaenopteridae*, all of which open their jaws wide to engulf masses of prey and possess a highly distensible throat pouch and extensible longitudinal grooves on the throat and belly. They occur in seas worldwide and range from 6 to 30 m in length. The only other living balaenopterid** is the Humpback Megaptera novaeangliae, and it is generally regarded as the sister-taxon to the rorquals. I’ve seen two explanations for the term rorqual. The commonest is that it derives from the Norwegian rørhval and means ‘grooved whale’ – a reference to those longitudinal grooves. The less common explanation is that it originated from the French for ‘red throat’, this supposedly being a reference to the reddish colour visible between the throat grooves when the whale’s buccal pouch is extended (Berta & Sumich 1990).
* Most books on whales state that there are five rorqual species. As with so many tetrapod groups, the number of recognised species has increased in recent years, both as ‘old’ species have been resurrected from synonymy (Antarctic minke B. bonaerensis and Pygmy bryde’s B. edeni), and as new species have been described (Omura’s whale B. omurai).
** Some workers have included the Grey whale Eschrichtius robustus within Balaenopteridae. It is mostly agreed, however, that Eschrichtius belongs to a small clade (Eschrichtiidae) best regarded as the sister-taxon to Balaenopteridae.
Rorquals grow fast, reaching sexual maturity at between 5 and 12 years of age in the larger species. They can produce up to 1.5 calves per 2-year period, though three years between calves is probably more normal. Pregnant females increase their weight by 26% and, thanks to lipids stored in their visceral fat and blubber, increase their total energy budget by a staggering 80% (Víkingsson 1995). After a pregnancy of 10-13 months, babies are suckled for 4-10 months and (in blue whales) are provided with 200 litres of milk a day. Unsurprisingly, babies increase their weight substantially during this time, with a 2-3 ton newborn blue whale putting on 90 kg a day, and reaching 20 tons by the time it is weaned. They are the fastest growing baby mammals. Rorquals are long-lived, with minkes B. acutorostrata reaching their forth or fifth decades, Sei B. borealis surviving to 65 or so, and Fins B. physalus to 85 or 90, or possibly 100. Incidentally, right whales (balaenids) are thought to survive into their second century, but they’re not rorquals.
We all know that rorquals are big, that they possess baleen, and that they feed by engulfing crustaceans, small fish and other prey. They spend summer in the polar regions, where they feed and put on weight, and then they migrate in the winter to the tropics, where they breed and give birth to their enormous calves… but they don’t _all_ do this, with some populations of some species being non-migratory. Of course, there’s more, a lot more, and in the next few posts I’d like to introduce a few details that you might not have encountered before… unless, that is, you’re a cetologist, or a close friend of one.
Thanks – mostly – to aerial photography, most of us are now familiar with the true body shape of live rorquals. They are shockingly gracile and incredibly long-bodied, with a shape that (when seen in dorsal view) has been likened to that of a champagne flute. While people had known this for a while (Roy Chapman Andrews wrote in 1916 of the Fin whale’s ‘slender body … built like a racing yacht’, for example), what may or may not be surprising is that only recently have people in general come to realize that rorquals are shaped like this. Basing their reconstructions on beached carcasses, or on rorquals killed by whaling vessels, artists and scientists had previously thought that rorquals were stouter, with fat bellies and flabby throats. Rorquals were still being depicted this way as recently as the 1960s, as in (for example) the excellent paintings and drawings of Sir Peter Scott [see above, borrowed from the Wildlife in Danger Brooke Bonds card set].
By photographing live sei and minke whales, underwater, from close range, Gordon Williamson (1972) argued that the traditional ‘baggy-throat’ reconstructions failed to show the true body shape of the animals. His drawings, reconstructed from his photos (which invariably failed to capture the entire animal in the frame), were dead accurate and among the first to depict rorquals in this way. Williamson’s whales were all captured, by harpoon, from a commercial whaling vessel. No explosive was placed in the harpoon head (normally, the harpoon head explodes within the body of the whale), so a harpooned whale was not killed immediately and was simply tethered to the ship. As it swam around, gradually tiring, Williamson approached it in the water and took his photos [the accompanying image, showing a young rorqual that beached in Florida in 2002, is borrowed from VisitGulf.com].
More on rorquals in the next post, this time focusing on the biomechanics of feeding: From cigar to elongated, bloated tadpole: rorquals part II. For the latest news on Tetrapod Zoology do go here.
Refs - -
Berta, A. & Sumich, J. L. 1999. Marine Mammals: Evolutionary Biology. Academic Press,
Stearn, W. T. 1981. The
Víkingsson, G. A. 1995. Body condition of fin whales during summer off
Williamson, G. R. 1972. The true body shape of rorqual whales. Journal of Zoology 167, 277-286.