Marine Mammals and the Oceans
marine mammal is a mammal that is primarily ocean-dwelling or depends on the
ocean for its food. Mammals originally evolved on land, but later marine
mammals evolved to live back in the ocean.
There are five groups of marine mammals:
1. Order Sirenia: the manatee, dugong.
2. Order Carnivora, family Ursidae: the polar bear
3. Order Carnivora, infrafamily Pinnipedia: the seal, sea
lion, and walrus
4. Order Carnivora, family Mustelidae: the Sea Otter and
5. Order Cetacea: the whale, dolphin, and porpoise
The Indianapolis Zoo is very lucky to have an excellent group of marine
mammals in its collection. Although these animals are cared for within
their own department at the Zoo, several of them are physically connected to
the new Oceans exhibit. While the dolphins and walrus have their own
habitats, the harbor seals, gray seals,
California sea lions
and the polar bears all have underwater viewing areas inside the Oceans
Photo by Tom Schoon
Mammals vs. Fish
Since mammals originally evolved on land, their spines are optimized for
running, allowing for up-and-down but little sideways motion. Therefore,
marine mammals typically swim by moving their spine up and down. By
contrast, fish normally swim by moving their spine sideways. For this
reason, fish mostly have vertical caudal (tail) fins, while marine mammals
have horizontal caudal fins.
Some of the primary differences between marine mammals and other marine life
• Marine mammals breathe air, while most other marine animals extract oxygen
• Marine mammals have hair, but Cetaceans have very little, usually a very
few bristles retained around the head or mouth. All members of the
Carnivora have a coat of fur or hair, but it is far thicker and more
important for thermoregulation in Sea Otters and Polar Bears than in seals
or sea lions. Thick layers of fur contribute to drag while swimming, and
slow down a swimming mammal, giving it a disadvantage in speed.
• Marine mammals have thick layers of blubber used to insulate their bodies
and prevent heat loss. Sea Otters and Polar Bears are exceptions, relying
more on fur and behavior to stave off hypothermia.
• Marine mammals give live birth. Most marine mammals only give birth to one
calf or pup at a time, and are never able to birth twins or larger litters.
• Marine mammals feed off milk as young. Maternal care is extremely
important to the survival of offspring that need to develop a thick
insulating layer of blubber. The milk from the mammary glands of marine
mammals often exceeds 40-50% fat content to support the development of
blubber in the young.
• Marine mammals maintain a high internal body temperature. Unlike most
other marine life, marine mammals carefully maintain a core temperature much
higher than their environment. Blubber, thick coats of fur, bubbles of air
between skin and water, countercurrent exchange, and behaviors such as
hauling out, are all adaptations that aid marine mammals in retention of
The polar bear spends a large portion of its time in a marine environment,
albeit a frozen one. When it does swim in the open sea it is extremely
proficient and has been shown to cover 74 km in a day. For these reasons,
some scientists regard it as a marine mammal.
Marine Mammals & The Oceans
Because humans and marine mammals share so much in terms of their
relationships with the oceans, it is important to learn more about how we
are related, how our actions affect each other, and what those actions can
mean for the health of the oceans on whose existence both of us ultimately
Marine mammals and people need healthy oceans to survive.
When the oceans are healthy, humans and sea creatures can thrive side by
side. When pollutants wash into the oceans, sea creatures and people
around the world suffer.
We share the coasts.
Nearly half the world’s population lives near the ocean, sharing the beaches
and waters with seals, sea lions and other ocean creatures. Things
that impact the health of the oceans impact all living creatures.
We share a taste for the same food – fish!
The average American eats about 27 pounds of saltwater fish a year.
Nearly all of a sea lion or seal’s diet is fish – and a lot of it. The
Zoo’s largest sea lion eats nearly 25 pounds of fish a day.
Soon there may not be as many fish around to eat.
Commercial fishing fleets are catching some fish faster than they can
reproduce and replace themselves. Some of the fish we love to eat –
like shark, Chilean sea bass and monkfish – may not be on the menu in a few
years. Fewer fish in the ocean will affect seals, sea lions and
We share threats to the oceans’ health.
Pollutants washed into the oceans can make fish dangerous to eat and the
oceans unhealthy to swim in. Many of the fish we think are tasty –
like shark, swordfish, wild caught striped bass and king mackerel – contain
so many toxins they may be risky to eat.