Baleen whales belong to the order Cetacea, the
only mammals which spend their entire lives in
the water of the earth’s oceans. There are seventysix
cetacean species, and the baleen whales make
up ten of them. Among baleen whales are blue
(sulfur-bottomed) whales, the largest animals that
have ever lived. They grow to lengths of over one
hundred feet and can weigh 400,000 pounds (200
tons). This makes them more than fifty times the
size and weight of a bull elephant andmuchlarger
than any dinosaur.
Like all whales, baleen whales are thought to
be descendants of a land animal, believed to have
been an early ungulate (hoofed mammal). The
huge size of the baleen whale is possible because it
lives in the water. This supports its mass and frees
it from the limitations of land animals, which can
only grow to the sizes and weights their legs will
support or their wings can carry into the skies.
Whythe ancestors of baleen whales entered the
oceans is not understood. It is guessed that the return
to the oceans was due to the need for a new
food supply or to escape frompredators. Most paleontologists
believe that it happened sixty million
years ago, twenty million years before the
first whale fossils occur.No fossil that links baleen
whales to their landbound ancestors has yet been
found, although the search goes on.
Physical Characteristics of Baleen Whales
The most characteristic physical feature of baleen
whales is that, rather than teeth, they have hundreds
of baleen plates hung vertically from their
upper jaws. The plates, with bristles on their inner
edges, capture the krill the whales eat. A feeding
baleen whale swims with its huge mouth open
and engulfs several tons of seawater containing
krill. Then the whale shuts its mouth, it presses its
tongue against the back of the baleen bristles, and
forces the water out of its mouth. This traps the
krill on the baleen plates.
In all whales, evolution yielded streamlined,
fishlike mammals. Furthermore, their front legs became
paddle-shaped flippers whose bones resemble
jointed limbs and digits. In contrast, the external
hind limbs disappeared, although in many
cases their vestiges are found internalized. The
horizontal tail flukes that propel whales are not
anatomically related to hind limbs. They are boneless
and shaped by fibrous and elastic tissues. Nor
are flippers related to fish tail fins, which differ in
composition and are orientated vertically.
The whale body is surrounded by a thick blubber
(fat) layer. This greatly enhances whale buoyancy,
insulates, and is an excellent energy storehouse. The insulating ability of blubber
may explain why whales living in
warm waters have much thinner blubber
layers than those living in cold waters.
In addition, a whale’s soft rubbery
skin lacks pores, sweat glands, and sebaceous
glands. It is hairless, except
for small patches on areas near the
chin and atop the head. These hair
patches support the theory that baleen
whales evolved from animals having
hair or fur.
Whales, like all mammals, have
lungs and breathe air through one or
two nostrils, depending on species, located
in a blowhole. Just prior to dives
whales close their nostrils tightly. If
kept submerged indefinitely, whales
would drown. Whale nostrils are located
on top of the head for functional
convenience in diving. They connect
directly to the lungs. Contrary to popular
belief, a whale’s visible “spout” is
not water. It is exhaled, warmed water
vapor and spent air fromthe lungs, plus any water
present in the depression around the blowhole.
Four physiological adaptations allow whales
to dive deeply and for prolonged time periods.
First, they have more blood than land mammals
and a huge capacity to store oxygen in blood and
muscle. Second, each whale breath replaces 85
percent of the air in its lungs, compared with 15
percent in land mammals. Third, whales can resist
the carbon dioxide buildup that triggers involuntary
breathing in land mammals. Consequently,
most baleen whales can hold their breath for an
hour or more under water. Finally, they are able to
restrict blood flow to various organs during deep
dives, limiting oxygen flow to inessential sites.
This protects the whale heart and brain from oxygen
deprivation in long dives.
Special Senses and Baleen Whale Intelligence
Baleen whales have small eyes, lack external ears,
and have brains much larger than those of humans.
These physical characteristics have led to
the belief that the whales use sound and hearing
in thewayvision and smell are used by landmammals.
Two kinds of sounds are made by baleen
whales: echolocation and vocalizations. Both are
thought to arise from air moving between nostrils
and the nasal passages that lead to the lungs
Echolocation sounds are thought to function
like biosonar, as in terrestrial bats. That is, whale
echolocation is perceived as the means by which
they explore the world around them. On the other
hand, vocalizations, such as the “songs of humpback
whales,” are perceived as the language by
which members of the same whale species communicate.
It is thought that the whale identifies
the size, distance, and other characteristics of an
object by the directing sounds made in a whale’s
head toward it and receiving sound waves that
bounce back off it. Evidence for the role of
echolocation is taken from observations made on
whales in captivity. In addition, some beached
whales have had parasites in their inner ears that
lead scientists to believe that the whales ran
aground due to losing the ability to echolocate
shorelines and stay away from them.
The great ability of water to carry and amplify
sound waves is deemed to be the reason why cetaceans
have been able to discard the external ear
that land mammals developed to gather airborne
sounds. Operation of this system of sensing
would have obvious use in navigating and in the
capture of prey in dark, often murky ocean water.
There it would provide the means to scan by
sound for the information almost all land mammals
get by seeing.
The unusual sensory capabilities of whales
have given rise to considerable speculation as to
their intelligence. This is stimulated by the observation
that cetaceans are the only animals except
elephants (with ten-pound brains) to have brains
larger those of humans (three pounds). For example,
an adult sperm whale has a twenty-pound
brain. However, the relationship of brain size to
intelligence, in this size range, is not clear.
Supporting the contention of brain size paralleling
intelligence, whales and dolphins show
considerable capacity for learning when studied
in captivity. Their great playfulness, intraspecies
communalism, and the affectionate care of offspring
make many people strong advocates of cetacean
“language” and great intelligence. These
concepts remain unproven.
The Life Cycle of Baleen Whales
Baleen whales reproduce in a fashion similar to
that in other mammals. Adults enter a period of
courtship. This includes side-by-side swimming,
body nuzzling, and body rubbing. Copulation
soon follows. The pregnant female carries her unborn
young for ten to sixteen months, depending
on whale species. Next, a large, very well-developed
calf (or occasionally, two) is born underwater.
Healthy whale calves can swim well at birth
and immediately find the ocean surface, with no
help from the mother.The calves nurse from two teats situated
in a pocket located on either side
of the mother whale’s genital opening.
Whale milk is white and very rich in
minerals, protein, and fat; as a result,
the calves grow quite fast. Usually a
whale calf that weighs one to two tons
at birth doubles its weight in the first
week. It is reported that nursing occurs
very rapidly.Acalf approaches the mother
whale, touches the nipple of the mammary
gland, and milk immediately and
copiously squirts into the calf’s mouth.
Mother whales are reportedly quite affectionate
to and protective of their offspring.
Young whales are weaned between
one and two years after birth, the age
at which most of them leave their mothers.
A whale is an adult, capable of reproduction,
by six to ten years of age.
The life spans of whales vary with maximumspecies
size. The smaller species can
live for thirty to forty years. The largest
species can live for as long as eighty years.
As with all other wild animals, not all
whales—in fact, relatively few of them—
survive to the ripe old ages noted.
Baleen Whales as an Endangered
Species
Past, uncontrolled whaling reduced the numbers
of almost all baleen whale species so much that
they are perceived as being endangered. At first,
quotas on whales were set by the International
Whaling Commission (IWC) for the purpose of
managing whales so as to allow the continuation
of the whaling industry. By the early 1990’s, most
major whaling nations belonging to the IWC had
stopped whaling. It is hoped that these actions, in
the absence of clandestine whaling, will allow baleen
whales to make a comeback by natural increase.
Only the future will tell whether this will
happen.
Classification:
Kingdom: Animalia
Subkingdom: Bilateria
Phylum: Chordata
Subphylum: Vertebrata
Class: Mammalia
Order: Cetacea (whales)
Suborder: Mysticeti (baleen whales)
Families: Eschrichlidae (gray whale), Balaenopteridae (rorquals,
two genera, six species), Balaenidae (right whales,
two genera, three species)
Geographical location: Every ocean on Earth
Habitat: Oceans
Gestational period: Varies between ten and sixteen months,
depending on species
Life span: Most estimates suggest eighty to one hundred
years for animals that survive into old age
Special anatomy: Baleen in the mouth; lungs like land mammals;
blow hole; flippers evolved from front legs; horizontal
tail; nasal cavity that produces echolocation and vocalization
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