Environmental Engineering Reference
In-Depth Information
2.2.5 Marine Mammals
whales of order
Cetacea
; the seals, sea lions,
walruses and sea otters of order
Carnivora
; and
the manatees and dugongs of order
Sirenia
. Each
of these orders arose independently from land
ancestors. They exhibit the mammalian traits of
being endothermic, breathing air, giving birth to
living young that they suckle with milk from
mammary glands and having hair at sometime in
their lives. All marine mammals share four com-
mon features:
Marine mammals spend their
life mostly or
entirely in water and possess
ns that adapt them
for their aquatic lifestyle. This is the most
advanced vertebrate group in the marine and
estuarine system. They have an insulating body
covering of hair to maintain their constant body
temperature (homeothermic) and have mammary
glands to suckle their young ones. They depend
completely on food of marine origin. Marine
mammals are placental mammals, which retain
their young ones inside their body until they are
ready to be born. This specialized organ, placenta
is present only during pregnancy. Although
marine mammals produce fewer offsprings than
other faunal species of seas and estuaries, most of
the young survive to adulthood because they
receive a great deal of parental care.
Mammals are adapted both to the terrestrial
environment and also in the sea. The presence of
hair (fur) of some and the layers of blubber in
others effectively reduce the loss of body heat to
the surrounding water. Like other warm-blooded
animals, mammals expend about 10 times more
energy, and hence, they need more food to support
their high metabolic rate. Being homoeothermic,
marine mammals are active feeders around the
clock and are adapted to wide range of habitats.
For example, baleen whales feed closer to the base
of the food chain, while sea otters and toothed
whales are second order or higher consumers.
Most marine mammals are quite intelligent
compared to other marine animals. This trait,
combined with their generally friendly nature,
makes them very popular with the common people.
Unfortunately, marine mammals share another
common characteristic as the bodies of many
contain materials that are commercially valuable to
humans. As a result, they have been hunted in large
numbers over centuries. During the last 50 years,
international conservation measures helped to
reduce the decline in population and the number of
some species is now increasing gradually.
About 4,300 species of marine mammals have
been documented. The three living groups of
marine mammals are the porpoises, dolphins and
Presence of
with limbs
that is adapted for swimming in the aquatic
phase. A slippery skin or hair covering reduces
drag.
streamlined body shape
Possess the power of
generating internal body
heat
from a high metabolic rate and conserve
this heat with layers of insulating fat, as in
most cases fur. Their large size gives them a
favourable surface-to-volume ratio; with less
surface area per unit volume, they lose less
heat through the skin.
Possess a highly ef
,
which is modied to collect and retain large
quantities of oxygen. The biochemistry of
blood and muscle is optimized for the retention
of oxygen during sleep, prolonged dives, etc.
cient
respiratory system
Reduction of
the
freshwater
requirement
through a number of
osmotic adaptations.
Minimal intake of sea water, coupled with
their kidney
s abilities to excrete concentrated
and highly saline urine, permits them to meet
their water needs with the metabolic water
derived from the oxidation of food.
'
Order Cetacea
Cetaceans
include the whales, which are the
most beautiful denizens of the ocean and repre-
sent the present-day survivors of the ancient
stock that reverted to the seas. The magni
cence
of whales is epitomized in the fact that whales
are the largest animals ever to inhabit the earth.
The blue whale for instance by reaching a length
of 100 ft and the weight of 200 tonnes (as water
can support its great weight) is 4 times heavier
than the dinosaur that roamed the earth earlier.
There are 79 living species of cetaceans which
