Marine mammals can be classified into the following orders: Cetacea (whales and dolphins), the Pinnipedia (lit. ‘feather
feet’ or seals, sea lions and walruses (Odobenus) ) and the manatees and dugongs (Sirenia, the sirens). The cetacens
can be divided into two suborders, the Odontoceti (toothed whales, odontocetes) which includes the dolphins, sperm
whales, killer whales, narwhals, porpoises and pilot whale; and the Mysteceti (baleen whales, mysticetes) including the
right whale, grey whale, blue whale, fin whale, sei whale, piked whales and humpback whale. Despite the size of whales
and the past, so ruthlessly exploited by humans, it is surprising how little is known about them. They have the freedom
of the oceans, diving to great depths and swimming vast distances, and this has made observations difficult, and often
such basic information, such as courtship behaviour, is completely unknown.
These animals include many remarkable examples of efficient ‘design’ and they hold a number of animal records
(largest, loudest, most complex animal-song, longest mammal migration). The Common dolphin can swim at 20-22 knots
(40-44 kph) for several hours. The Blue Whale is the largest and loudest animal on Earth. A Californian Grey Whale
can cover 80 nautical miles in a day’s swimming of 20 hours. As mammals they nurse their young. On the under-surface
of a whale are characteristic mammalian features – a navel, between this and the anus is the genital groove, which in
the female is flanked by one pair of mammary grooves, with the mammary glands internalised for streamlining purposes.
There are no hairs, however, except for a few sensory bristles around the head. As mammals, they are endothermic
(‘warm-blooded’ meaning they generate their own body heat) and so require insulation. Insulating blubber can account
for up to 30-45% of some cold-water whales (e.g. bowhead whales) and can be up to 2 feet thick.
As air-breathers, whales clearly exhibit some unusual adaptations. The lungs may hold 2000 litres of air and whales
must surface periodically to breath. It is thought that air sinuses in the base of the skull contain nitrogen-absorbing oils,
helping to prevent whales from suffering the bends during their rapid and deep dives. They have more than ten-times
the usual concentration of enhanced myoglobin in their muscles, a pink pigment which stores oxygen. They can
function for longer without oxygen, before the inhibiting burning of lactic acid builds up in their muscles. When diving,
blood is diverted away from non-essential systems and reserved for essential organs such as the brain. During
breathing, the lungs can apparently be ventilated more deeply than in terrestrial mammals, with 90% of the air being
changed with each breath.
Intelligence. The largest animal brain recorded was 20 lb for the brain of a sperm whale (though this is a small fraction
of its total body weight). Dolphins have brains a little larger than a human’s and about 1.2% of their body weight (a
human’s brain is about 1.93% of body weight) and it is thought that dolphins are highly intelligent. Many whales and
dolphins show social behaviour, caring for their sick and young, but in some species also exhibiting acts of great
violence. As we shall see below whales (and of course dolphins) often exhibit complex social behaviour.
Lifespan. Most whales live around 30-70 years, but bowhead whales may live for 150-200 years, on the basis of the
discovery of old spoon and harpoon tips in recently killed specimens that had survived earlier hunts. This is a very long
lifespan for a mammal; mammals have high metabolic rates and so tend to have shorter lifespans than reptiles of a
similar size. Despite their long lifespan, cetaceans do have relatively high metabolic rates, and the thyroid gland is large.
Sense organs. The ear bones are enclosed in bony capsules that are almost mechanically isolated from the rest of the
skull (only a narrow bony connection joins the two) by an envelope of oily/foamy air-sacs that enclose the ear-capsules.
The oil inside these air sacs absorbs nitrogen and equilibrates the pressure across the eardrum when diving (in
terrestrial animals the eustacian tube connecting the ear to the throat can perform this function, but when diving whales
can not utilise this). The mechanical isolation of the air is also important acoustically, it ensures that sound is channeled
mostly through the eardrum, rather than through the skull (as can easily happen under water). The bones of the ear
capsule are the densest in the cetacean body, perhaps helping to ensure that sounds passing through the head do not
easily penetrate the capsule, which resonates at a different frequency.
The snouts of toothed whales contain a cushion of adipose tissue, above the upper jaw, called the melon, which it is
though acts as an acoustic lens to amplify the whale’s sonar during echolocation. It has also been suggested that this
organ, which is richly supplied by nerves, is a sensor that can detect the flow of water when the whale swims, allowing it
to gauge its velocity. The few hairs/bristles that occur on the heads of whales may be sensory.
Excretion. The kidneys are relatively large (accounting for 1.1% of the body weight in the bottlenose dolphin) and well
lobulated, being divided into about 400 lobules in the dolphin and up to 3000 lobules in the largest whales.
Digestive System. The first chamber of the stomach is an expansion of the oesophagus (proventriculus) and contains
stones for grinding the shells of crustaceans, etc. This structure is lacking in squid-eating beaked whales. The second
stomach chamber is the fundic chamber or fundus (the stomach proper, the ‘fundus’ is that part of a hollow organ
furthest from the opening(s)), which releases protein-digesting pepsin, fat-digesting lipase and hydrochloric acid. The
third and final chamber of the stomach is the pyloric chamber or pylorus, which connects to the duodenum of the small
intestine. The junction between the small and large intestines is not distinct. The liver of whales may weigh as much as
one ton.
Respiratory System. Whales are mammals and have lungs that breath air and so they must surface periodically to
ventilate their lungs. When diving, some of the air moves from the alveoli into the bronchi, where it is stored until
needed before passing back into the alveoli. Storing the air in the bronchi reduces nitrogen-absorption into the
bloodstream under high pressure and this reduces the risk of bends when the animal surfaces.
Cardiovascular System. The heart of whales beats at about 8-23 beats per minute (bpm) whilst in dolphins it beats at
about 120 bpm.
Skin. The epidermis is relatively thin (less than 1 cm thick) with few dead cells, instead living cells extend almost to the
surface and the surface-most cells still retain their nuclei. (In terrestrial animals the outer layers are dead and
keratinised for protection against dehydration and also to protect against abrasion). This might account for the fact that
whale skin is easily scarred. The dermis is also relatively thin. Beneath the dermis, however, is the thick layer of
blubber, which insulates the animal and also acts as a valuable fat/fuel store. The skin is very mobile, being only loosely
attached to the underlying blubber and easily deforms when the animal swims, forming standing waves or ripples at
right-angles to the direction of motion. It has been argued that this arrangement reduces drag greatly, though others
have refuted this. Certainly, the boundary layer appears laminar rather than turbulent as the water flows smoothly over
the surface during swimming.
Reproduction. Due to the difficulties of observing whales much remains mysterious about their reproductive behaviour
(humpbacks are one of the better observed and are discussed below). The penis of cetaceans is generally very mobile,
and male dolphins use their penises as exploratory fingers (which possibly is misinterpreted by observers). Streamlining
is essential and the penis is kept retracted, by retractor muscles, when not in use, coiling into an S-shape and held
beneath the abdominal skin when not in use. The penis may be over 3 m (10 feet long) and 30 cm (one foot) in
diameter in the largest whales. When in use, the anterior part extends through the urogenital slit, being extended largely
by its elasticity rather than by hydrostatic pressure. There is no scrotum, the testes are situated inside the abdomen,
and spermatogenesis (sperm generation) can occur at body temperature (in most mammals it requires a slightly lower
temperature). The mammary glands are also internal, the nipples projecting through the pair of mammary slits during
suckling. The vulva is slit-like and lacks pronounced labia minora (minor lips) and so again streamlining is optimised.
Cetaceans are placental mammals. The newborns suckle for 6 months to two years and the highly concentrated milk
ensures their rapid growth. Contraction of specialised cells in the mammary glands, ensures that milk is squirted into the
throat of the suckling young. Blue whales are thought to begin reproducing by five or six-years of age. A minimum time
period of about two years elapses between successive births. The newborn blue whale calf is about 8 m (25 feet) long,
weighs two tons and can swim immediately.
It is impossible to do justice to the whales in a single article, so we shall focus one a couple of examples of whales in
depth.
Rorquals (Fin Whales)
This family of baleen whales including the Fin Whale and the Blue Whale. The Blue Whale is the largest living animal on
earth, and possibly the largest (heaviest though not the longest) of all time. (The contenders are the very largest
sauropod dinosaurs, whose weight estimates vary hugely, but are usually about 100 ton, and perhaps prehistoric
whales). The Blue Whale (Balaenopterus musculus) reaches about 33 m (100 feet) in length and weighs up to 130 tons
(196 tons is the recorded maximum). It is a dark slate blue, sometimes with paler mottling. Males and females are of
similar size, females slightly larger. The heart of a blue whale is about as large as an automobile and as heavy as an
elephant and a man could swim down the largest artery (the aorta)! They have the loudest voice of any animal on
Earth, reaching 188 decibels (equivalent to a space rocket launching). They can be heard a thousand miles away!
These whales may produce loud moans, each note lasting half a minute or so. They also produce ultrasonic bursts of
sound when feeding (pulses of 21-31 kHz) for echolocation, possibly using them to locate the shoals of krill on which
they feed.
Swimming. The body is torpedo-shaped (when not feeding) and the Blue whale is a fast-swimmer, cruising at 3-4 knots,
frequently maintaining 10-12 knots submerged and sprinting at 10-16 knots. They may remain submerged, holding their
breath, for up to two hours, but as mammals with lungs they must eventually surface to breath. When they do, the blow
reaches 6-12 m (20-40 ft) in height. Typically they will make about 20 shallow dives of about 20 seconds duration each
and then one longer dive of 30 minutes. They typically surface calmly and parallel to the surface.
Feeding. As baleen whales, with no teeth, blue whales are filter-feeders. They feed almost exclusively on krill (pink
shrimp-like crustaceans). The mouth and throat expand to huge proportions, enabling the whale to scoop-up its own
body weight in water! The throat then constricts, forcing the water out through the baleen plates, which act like a sieve,
keeping the shoal of krill inside, which is then swallowed. Despite eating such small animals, this feeding method is very
efficient, enabling the whales to grow to their massive sizes. In the Antarctic they seem to eat little but krill, which form in
shoals in well-lit waters at about 40 m from the surface, but in other water, other crustaceans may be included, and
small fish may be accidentally incorporated. They migrate to the antarctic during the 120-day krill season. Each krill
weighs about 1g and each whale may swallow 4 tons a day! When sea ice covers the surface waters they migrate to the
equator.
There are up to 400 x 2 baleen plates in the upper jaw. There are 60-100 ventral grooves (pleats) on the underside of
the throat and chest, allowing the skin to stretch when the throat expands massively during feeding, and possibly
allowing easy expansion of the chest during deep breathing. these grroves may also have some hydrodynamic function
during swimming.
Reproduction and behaviour. Blue whales form groups of 2-4 individuals, or occur singly, but form larger associations
for breeding and feeding. Packs of killer whales will sometimes hunt blue whale calves, or sick and weak individuals –
targeting the soft areas such as the tongue. The Blue Whale’s penis is over 3 m (1o feet) in length and totally
retractable (so as not to disturb the streamlined shape during swimming). Gestation lasts 11-12 months and the calves
are born in tropical waters, in-between the krill-feeding seasons. The calve eats about 600 litres of milk a day, and
hence doubles its weight in a week. Calves are about 8 tons at birth and 7 m (23 feet) in length. Females breed every
2-3 years.
Blue whales used to be global in extent but they have yet to recover their populations from whaling. Evidence suggests
that whaling pressures triggered an increased reproductive rate, with whales maturing earlier and growing to a smaller
maximum size. Their large size is not only a consequence of their efficient feeding method, but is also an advantage in
enduring cold Antarctic waters and ensures that, other than killer whales and humans, these animals have few
predators. Blubber provides insulation in the cold waters, but blubber decreases when they migrate into warmer waters
which have less food and also during the demands of pregnancy and lactation.
Humpback Whale (Megaptera novaeangliae)
Humpback whales have huge winglike flippers, about 5 m (16 feet) long, hence the name (megaptera literally means
‘great wing’). Adults average about 15 m (50 feet) and 34-45 tons, maximum 17.5 m (58 feet) and 53 tons, and females
are slightly longer than males. The flippers are scalloped on their leading edge, and the fluke is similarly serrated on its
trailing edge. The flippers are white below, mottled black and white above. The underside of the flukes has a black and
white pattern unique to each individual. The body is more rounded than that of the rorquals. Unlike rorquals, the
humpback raises its tail flukes above the water’s surface before sounding (diving deep). The blow is about 3 m high and
broad and balloon-like. The rough skin harbours many parasites and epizooites, with up to 450 kg of barnacles being
carried by an individual! These barnacles develop in cold waters but tend to drop off in warm waters. A whale lice,
Cyanmus boopis, is also specific to humpbacks. Remnants of internal hindlimbs occur in some individuals.
Feeding. Of particular interest is the hunting methods used by humpbacks. They typically lunge at their prey from below
with their huge net-like mouths open, swallowing shoals of fish or krill. The Alaskan population has a more sophisticated
method. They create a bubble net to trap and concentrate the prey while it can be swallowed. They force air out of their
blowholes at 15 m (50 feet) depth as they swim upwards in a tight spiral, before surfacing with open mouth to scoop the
food in the middle of this circular curtain of bubbles. Two whales may collaborate on making a larger net, up to 30 m in
diameter.
Reproduction and Social behaviour. Humpbacks form groups of 3-4 individuals, though separate groups communicate
with one-another, with their calls travelling hundreds of kilometres, such that a ‘herd’ is a loose collection of smaller
groups. Mating occurs in communual breeding grounds, in shallow warm waters. When courting, the males sing and
produce the longest and most varied songs in the animal kingdom. Sequences of 10-15 minutes duration repeat
for hours. A group of males will chase each female, who puts them through their paces to select the fittest and
strongest. The males will repel other males by thrashing their tail flukes and they will also fight, violently ramming and
jostling for lead position. They probably bite also, as the wounds sustained are often bloody and lead to scarring. Such
a battle has been recently filmed for the first time (BBC external link; the BBC website is a good resource on animal
behaviour). Eventually, the female will select her mate and then the couple may emerge embraced, vertical in the water,
heads above the surface, clasping one-another with their flippers, belly-to-belly in the mating position.
The humpbacks are thought to undergo the longest migration of any mammal, swimming 5100 miles a year from Central
America to their feeding grounds off Antarctica (Science Daily, external link).
Sperm whales (Physeter macrocephalus)
The sperm whale is the largest toothed whale and a major predator, feeding mostly on squid, including giant squid, but
also deep-sea sponges and fish, including the occasional shark. Giant squid weigh as much perhaps as 3 ton and so
are no match for a sperm whale, but they are not entirely defenceless, with powerful beaks and arms armed with
suckers which inflict superficial wounds on the heads of sperm whales, resulting in characteristic scarring. The males
reach about 20 m (60 feet) in length and 40 tons in weight. The females are rarely more than half the length of the
males. The skin is dark bluish-grey (steel-grey), lighter on the flanks and light grey or white on the belly. The brain
weighs about 10 kg. Occasional all-white individuals (like the mythical Moby Dick) have been found.
The upper jaw lacks teeth (but contains non-functional tooth germs in the gums) but the lower jaw has (16-30) x 2
conical teeth, each about 8 inches (20 cm) long. When the jaw is closed, the teeth sit in recesses in the upper jaw.
These recesses are lined by tough fibrous tissue. The neck vertebrae are fused, except for the atlas, which is free to
move (the atlas is the first cervical vertebra on which the skull articulates for nodding movements and is named after the
ancient Greek god who carried the Earth upon his back).
Diving. The Sperm Whale possesses a characteristic spermaceti organ, which gives the head its characteristic shape
and large volume; the head occupying about one-third of the total length of the animal. The blowhole is single,
S-shaped, and placed on the left side near the front of the head. This asymmetry distorts the skull which is also
asymmetric. The top-front of the head contains the large spermaceti organ, a reservoir or case of spermaceti oil which
solidifies upon cooling or on contact with air. Beneath this is a mass of sponge-like elastic fibrous tissue also filled with
oil in its spaces. When diving they apparently draw water into their long nasal passages (the right one is up to 5 m long
and 1 m in diameter) this cools and solidifies the spermaceti, increasing the density of the whale to achieve neutral
buoyancy. This allows them to remain motionless at depth, waiting in ambush for giant squid. (In many ways that is like
the ballast tanks of a submarine). The sperm whale is the deepest diving mammal.
There is no dorsal fin, but there is a series of dorsal ridges, the largest one at the front being called the ‘hump’. The tail
flukes are about 4 m (12 feet) across with a notch in the middle. These whales cruise at 3 knots (6 kph), but can ‘sprint’
for ten minutes at over 10 or 20 knots (40 kph). Sperm whales are remarkable divers, diving faster and much deeper
than can a modern nuclear submarine. It is thought that they can dive to at least 3000 m, descending at 4 knots and
surfacing at 5 knots. They can remain submerged, holding their breath, for more than an hour. When they surface they
breath six times every minute (about once every 10-15 seconds) and surface for about ten minutes between dives. The
blow shoots up about 3-5 m (10-15 feet) and is off to the left and forward at about 45 degrees. The males take about 50
breaths before diving for 50 minutes, the females 30 breaths before diving for about 30 minutes. After a very deep dive
they bolt to the surface, breaching with such force that they lift out of the water and splash down with a clap that can be
heard 4 km away. The first exhalation after a deep dive is explosive and can be heard one or more km away! (Is this the
‘roar’ produced by breached sperm whales?).
Reproduction and behaviour. Sperm whales are found in all the Earth’s oceans, but are especially frequent off the coast
of Peru and the Galapagos Islands, where squid are abundant. They are polygamous, the males or bulls mating with
several females or cows, and the younger males will drive off the old males to gain dominance of the herd. Aggressive
rogue-males may break away from the herd and live solitary lives. During the mating season the males fight, frequently
scarring one-another’s skin. They may ram one-another or lock jaws and roll around at the surface until one male
submits, often minus a few teeth. If threatened, sperm whales are particularly aggressive, and they will repeatedly ram
whaling ships or ships that happen to accidentally collide with one of the herd. (Sperm whales often sleep deeply for
hours near the surface and are sometimes killed when large ships collide with them). Ships have been sunk by these
attacks, and even modern steel-plated ships significantly damaged. Nursery school herds consist of about 20-30
individuals, mature females and nursing calves. Groups of up to 20 younger males may form bachelor herds, whilst
harem herds may consist of up to 80 individuals. Their movements appear to follow a lunar cycle, with herds of whales
aggregating in much larger groups, of up to 1000 individuals or more, at full moon, gathered above oceanic ridges. (Are
they tracking squid?)
Gestation lasts 14-16 months and lactation for a further one or two years. Usually a single calf is born. When giving
birth the female stands vertically in the water, with her head above the surface, whilst other females, the midwifes, circle
around her for support, forming a so-called ‘maternity ward’. Members of the herd will also support a sick or injured
individual, circling around them, heads inwards, to support the individual, continuing to do so until that individual is
recovered or dead. Whalers have exploited this situation, circling round the backs of the nursing animals and picking
them off one-by-one. If attacked by killer whales, they may form a protective circle around their young, with heads facing
outwards.
Sperm whales produce a series of clicks or squeaks o bursts of sounds that are used for echolocation and
communication. Each individual has a distinctive voice. Pressures from whaling have resulted in a faster rate of
maturation with first pregnancy occurring at an earlier age, so as to boost reproductive rates.
Ambergris is obtained only from the sperm whale. This is a blackish or brownish-grey mass, up to 400 kg (900 lb) in
weight. It is produced in the intestines, but often found free floating in the water or washed ashore. When fresh it has a
foul odour, but upon aging it acquires a musky, earthy-odour. When dry, it resembles dried tar or bark and often has
squid beaks embedded in it. (It may be formed around these beaks to prevent irritation inside the animal). It dissolves in
organic solvents and was once as valuable as gold because of its use as a source of carrier oil in the perfume industry –
it retains more volatile odoriferous essential oils well. Nowadays, there are synthetic substitutes.
Whale Conservation
I recall that the Blue Whale was at one time feared extinct. It was only the campaigns fought by conservations to
regulate/ban whaling that has allowed this and a number of other whale populations to recover from an endangered
level. Many whale populations are still far below their pre-whaling levels. The global population of blue whales was
originally about 200 000 to 300 000, but hunting drove their numbers down to several hundred. The remaining few
were, understandably, more wary and elusive and for a time sightings ceased. There were also fears that if they could
not find one-another to mate, that they may enter terminal decline. However, their numbers are now steadily increasing
and a 2002 estimate places their population at 5000 to 12000. There are fresh concerns about climate change. A
number of whale species, including blue whales, depend on the large production and concentration of krill in cold
Antarctic waters and it is feared that their food stocks may decline with global warming.
References
R.J. Harrison and J.E. king, 1965. Marine Mammals, Hutchinson University Press.
Lyall Watson, 1981. Whales of the World, Hutchinson (pub).
David Attenborough, 1990. The Trials of Life, BBC Books.
The BBC (e.g. http://news.bbc.co.uk/earth/hi/earth_news/newsid_8318000/8318182.stm,
http://www.bbc.co.uk/nature/life/Sperm_whale)
Science Daily (http://www.sciencedaily.com/releases/2007/04/070410091423.htm)