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MAMMAL NAMES | Super-Sized Cetaceans:

The Gigantic Forms & Features of Ireland's Baleen Whales

The size of the blue whale, which can weigh as much as 30 male African elephants, is emphasised by the fact that the smallest form, which still weighs 70 tonnes and measures 24 metres in length, is called the pygmy blue whale

Last month we were given a general introduction to the baleen whales in Ireland’s seas, and learned much about the baleen from which their common name and many other names derive. So, over the next few months we will take a closer look at these seven species of cetacean, beginning with that aspect of their form which is the most obvious and imposing – their super size. Delving into the dimensions of these whopping whales is truly head-spinning, and it is no surprise that a number of their names relate to their gigantic forms and features, and that these also confer many heavyweight titles on them. So, it is time to buckle up and prepare to feel very small, as we once more sail into the sea to meet Ireland’s super-sized cetaceans.

To find a name that makes a direct reference to the massive size of Ireland’s baleen whales, we need look no further than the Irish term for ‘whale’ itself, as this, míol mór, which we have previously encountered, literally means ‘big beast’.

The incredible size of the baleen whales in Irish waters is underlined by the fact that the smallest of them, the northern minke whale, still measures around nine metres in length and weighs a hefty nine tonnes, making it considerably bigger than one of the larger toothed whales, the killer whale, males of which usually only reach eight metres in length and almost five-and-a-half tonnes in weight. Newborn calves of the northern minke whale alone weigh around 350 kilograms – almost twice the weight of an adult male red deer, which is the largest of Ireland’s native land mammals.

So, by any measure, the smallest of the baleen whales in the waters off the Irish coast is itself a giant. But, of course, being a member of a mammal group that includes not only the largest living mammals, but some of the largest animals ever to inhabit the Earth, the northern minke whale’s dimensions pale in comparison to the other baleen whales whose vast forms cruise through Ireland’s extensive territorial seas.

Indeed, one of the northern minke whale’s Irish names makes direct reference to the fact that it is generally similar in form, but smaller than, one of the largest baleen whales in Irish waters, the fin whale. Like its English name, one of the fin whale’s Irish names, droimeiteach, refers to its relatively large dorsal fin, with drom meaning ‘dorsal’ and eiteach meaning ‘fin’, while the northern minke whale is called droimeiteach beag, with beag meaning, unsurprisingly, ‘small’. In Irish, then, the northern minke whale is the ‘small fin whale’.

From the illustrations of the northern minke whale (L) and fin whale (R) above, it is easy to see why the former is sometimes referred to as droimeiteach beag in Irish, the 'small fin whale'

So, the northern minke whale shares Irish waters with fellow baleen whales that are true titans, and their super size is swiftly revealed by a quick look at their jaw-dropping dimensions.

The next smallest, the sei whale, grows to an impressive 19 metres long and 30 tonnes in weight in the Northern Hemisphere, and, as is true of all baleen whales, grows even larger in the seas of the Southern Hemisphere, where it can reach 21 metres in length and tips the scales at 35 tonnes. The other five baleen whales known from Ireland’s seas are, though, in yet another league in terms of size.

The humpback whale, although on average reaching only 16 metres in length, can weigh up to a gigantic 65 tonnes. The northern right whale can be even larger, up to 18 metres long and 40–70 tonnes in weight in the North Atlantic, and is even bigger in the North Pacific. Its relative, the bowhead whale – an arctic species that was spotted in Irish waters for the first time as recently as 2016 – is another gargantuan form, measuring up to 20 metres in length and a whopping 60–80 tonnes.

The fin whale outdoes even these eye-watering statistics, though, with a length of 24 metres and a weight of 70 tonnes in the Northern Hemisphere, while in the Southern Hemisphere this rises to 27 metres in length and 80 tonnes in weight. What’s more, estimates for the maximum weight that this titanic form can reach range from 90 tonnes to almost 120 tonnes, which would mean that the largest fin whales could conceivably weigh as much as 20 African elephants!

And yet, as super-sized as the fin whales are, they are outstripped in scale by the very largest baleen whale in the seas of Ireland, or anywhere else for that matter; that colossus among colossi, the capo di tutti capi – the blue whale.

Size of the largest baleen whales in Ireland's seas, from the blue whale (top, red) to the humpback whale (middle, green)

The dimensions of this leviathan are truly mind-boggling. The form which swims through Irish seas, the northern blue whale, measures 24–27 metres in length and weighs a staggering 130–150 tonnes. As ever with the baleen whales, though, it is on average even larger in the Southern Hemisphere, measuring 27 metres and 150 tonnes in weight, while the highest weight ever recorded, of a female captured in the southern Atlantic off the coast of the island of South Georgia in 1947, was an incredible 173 tonnes. And as we’ve already seen with the fin whales, the estimates for the blue whale’s maximum size are even greater, and it is thought that it can possibly reach a weight of 180 tonnes – as much as 30 African elephants!!

And while the blue whale’s longest recorded length, 33.6 metres, is considered dubious, it can still claim a scientifically validated maximum length of just under 30 metres (29.9 metres, to be exact). To put this spectacular length in context, it is almost five times the greatest length ever recorded for a great white shark (6.4 metres).

The largest blue whales are around five times longer than the largest great white sharks

Considering it is a super-sized creature of such unrivalled dimension, it is quite unexpected to learn that one of the blue whale’s names possibly refers to, of all things, the mouse. Although the blue whale’s Irish name, míol mór gorm, means the very same thing as its English name, its scientific name is Balaenoptera musculus, and though this species name, musculus, can mean the very fitting ‘muscle’, it can also mean ‘little mouse’, as we previously saw when meeting Ireland’s house mice. Some have suggested, then, that the name of this giant whale contains a little joke. The confusion here arises from the fascinating fact that in Latin muscles and mice are truly related, the word for muscle, musculus, deriving from the Romans' view that the bicep looks like a little mouse running under the skin.

In any case, just how large the blue whale is is also emphasised by the name of a form of this species we have yet to meet. We have already encountered two subspecies of the blue whale: the northern blue whale, Balaenoptera musculus musculus, and the larger Southern Hemisphere subspecies, Balaenoptera musculus indica. However, there is another form also found in the seas of the Southern Hemisphere, Balaenoptera musculus brevicauda, which, at a weight of 70 tonnes and a length of 24 metres, is both lighter and shorter than the other forms, hence its subspecies’ name brevicauda, which comes from two Latin words: brevi, meaning ‘short’, and cauda, meaning ‘tail’. It is its common name which truly highlights how large the other two are, though, as it is known as the pygmy blue whale. Only when it comes to the blue whale could a 70-tonne monster that is around twice the length of a double-decker bus qualify as a pygmy.

Many of the features of the blue whale, then, scream of its super size, and it can claim many heavyweight titles. It has the world’s largest mouth and the world’s largest tongue, which by one estimate weighs over three-and-a-half tonnes, making it heavier than a female elephant. It has the world’s largest heart, which is the size of a car, while it is said that a child could crawl through its arteries. Females give birth to the largest newborns in the world, which, at seven metres long and around two-and-a-half tonnes in weight, are heavier than a male white rhino, which is the largest rhino species in the world. Not to be outdone, the males impregnate the females with the largest penises in the world, which measure somewhere between two-and-a-half and three metres in length. Blue whales indeed.

Newborn blue whales are even larger than adult male white rhinos

However, the blue whales cannot claim all the heavyweight titles available, and though they hold the title for the largest penis on Earth, it is another baleen whale in Ireland’s seas, the northern right whale, that holds the title for largest testicles. The titanic testes of this whale weigh in at over 800 kilograms, making them heavier than a large grizzly bear!

Another feature in which the blue whale is outdone in super size by one of its fellow baleen whales in Irish waters is the pectoral fins. The humpback whale possesses absolutely gigantic pectoral fins, which are the longest of any whale and can measure up to around one third of its body length. In fact, it is from this very obvious feature that its genus name, Megaptera, is derived, composed as it is of two Greek words: megas, meaning ‘huge’, and pteron, meaning ‘wing’ (as we previously saw when we met Ireland’s bats).

Humpback whales use these super-sized flippers to do a range of dramatic acrobatic manoeuvres, something you might not expect from a whale with the decidedly unathletic-sounding English name ‘humpback’, and the even less athletic-sounding Irish name, míol mór dronnach, which means ‘hunchback whale’. These names, though, do not refer to any particular malformation in this whale’s general appearance, but rather to its habit of arching its back as it dives under the surface of the water, a behaviour which is more noticeable in this species due to its dorsal fin sitting atop a mound of blubber.

A humpback whale dramatically breaching, showing off the massive pectoral fins from which its genus name Megaptera, meaning 'huge wing', is derived

And when underwater, the humpback whale engages in other impressive activities. One of these, bubble-netting, refers to one of the ways it preys on fish, blowing sprays of bubbles to coral them into a tightly-packed shoal and then ploughing upwards through them with its massive mouth open to fill its belly.

Of the humpback whale’s fellow members of the family Balaenopteridae in Ireland’s waters – namely, the northern minke whale, sei whale, fin whale, and blue whale – almost all eat fish to some degree. But while in the smallest species, the northern minke whale, fish are the main component of the diet, the larger forms rely more on eating zooplankton, made up of tiny marine organisms. In fact, the largest balaenopterid, the blue whale, is the only member of the family that does not gobble fish, instead feeding exclusively on zooplankton, chowing down on vast quantities of krill, which are tiny shrimp-like crustaceans, as well as other tiny crustaceans called copepods. As it is succinctly put in The Encyclopedia of Mammals edited by David W. Macdonald: ‘The biggest animals in the world keep themselves alive by eating some of the smallest.’

In fact, the sei whale even owes its common name to its habit of eating zooplankton, as ‘sei’, which is pronounced ‘say’, derives from the Norwegian word for ‘pollock’, seje, due to the fact that it arrives off the coast of Scandinavia around the same time as this fish every year, both seeking to make a meal of the same zooplankton.

The common name of the sei whale (top) derives from its search for the tiny marine organisms that make up zooplankton, such as northern krill (Meganyctiphanes norvegica) (bottom)

Compared to these tiny marine organisms, the sei whale and the other baleen whales in Ireland’s seas seem to become, if it is possible after everything we have learned, even larger to our eyes. Beneath the waves they are the unquestioned rulers of their domain, each one like a floating city that contains multitudes. Their gargantuan dimensions are not the only thing that makes them special, of course, but they are surely the first thing to capture our attention, and that this has long been so is attested to by the many names we have encountered that relate to this aspect of their form. No less than the people that came before us, we are simply awed by the sheer bulk of these aquatic giants, and it is a wonderful thing that Ireland’s seas are populated by such a rich diversity of super-sized cetaceans.

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