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There are 33 species of pinnipeds
(meaning "wing-" or "fin-footed")
which include 13 true seals, 14 eared seals (sea lions
and fur seals), and 1 walrus. California
sea lions belong to the family Otariidae
which means "little ears.” In the scientific
community, there are many debates concerning the ancestry
of eared and true seals. Some scientists believe that
eared seals and walruses may have evolved 30 million
years ago from bear-like creatures in the North Pacific,
and that seals evolved from otter-like carnivores in
the North Atlantic.
Seals vs. Sea Lions: Is there a difference?
Seals and sea lions have several visible differences.
Sea lions have external ear flaps, whereas the majority
of seals have a small opening for an ear and lack an
external ear flap. A flexible pelvic girdle enables sea
lions to move more easily on land by rotating their hind
flippers underneath their bodies and walking like other
four-legged animals. To move on land, seals propel their
streamlined bodies in a way similar to a caterpillar.
Both seals and sea lions are professionals in the water
environment. Sea lions use their large front flippers
to propel themselves through the water. Seals use their
hind flippers in a side-to-side motion.
How fast can a sea lion swim?
Sea lions can swim in burst
speeds up to 25 mph, but generally cruise at approximately
11 mph. Sea lions gain speed by porpoising, gliding
on the water's surface to minimize resistance. Surfing
in front of waves or large whales seems to be a fun
activity for sea lions. Sea lions have often been called
the “Angels of the
Sea” due to the unique way that they swim. Sea
lions will use their hind flippers to steer and swim
using their front flippers. True seals usually swim at
about 6 mph and can reach speeds as fast as 18 mph. Walruses
tend to take a relaxing approach to the water, averaging
speeds of 6 mph or less.
How long do sea lions live?
The average life span of a sea
lion is around 20 years, although some
have been recorded to live into their 30s. Age is
determined by counting growth layers in their teeth,
similar to counting rings in a tree trunk. Scientists
have noticed that males tend to live shorter lives
than females.
What do sea lions eat?
Sea lions feed on a variety of organisms including
various fish (anchovies, herring, salmon, rockfish, and
hake), squid and octopus. Sea lions at Dolphin Research
Center eat herring, smelt, and capelin. Wild sea lions
often feed cooperatively, eating 5 - 8% of their body
weight each day, which is between 15 - 35 pounds (7 -
16 kg) of food. Sea lions have 34 to 38 teeth, specially
designed for grasping and tearing their food; however,
their food is swallowed whole. Most of their water intake
comes directly from the fish they eat, although they
may occasionally drink small amounts of seawater while
fasting throughout the breeding season. Rocks, sometimes
found in the stomachs of sea lions, may create a false
sensation of fullness during the fasting period.
Do sea lions have good senses?
Hearing: Sea lions hear both above
and below the water's surface, although they hear better
under water. Studies show sea lions can hear frequencies
up to 70,000 Hz, but tend to vocalize within a range
of 100 to 10,000 Hz. This is comparable to humans who
have a hearing range of 20 to 20,000 Hz. Sea lion vocalizations
include barks, clicks, moans, chirps, growls, and squeaks.
There is no concrete evidence to suggest that sea lions
use echolocation.
Sight: Sea lions, like many marine
mammals, can see well both above and below the surface
of the water. Unlike humans, sea lions may not see in
color. They can possibly discriminate colors in the blue
- green spectrum. All pinnipeds have a membrane at the
back of each eye called a tapetum lucidum to aid in night
vision. Cats also have a tapetum lucidum, which is why
the eyes of both cats and sea lions glow at night. On
land, their eyes are protected by a nictitating membrane,
which wipes away sand and debris.
Smell: Sea lions cannot smell underwater
but, above water, smell is a highly developed sense.
Females use smell for pup recognition and males use it
for breeding purposes to locate females in estrus.
Taste: Sea lions have a limited sense
of taste, similar to other marine mammals.
Touch: Sea lions are tactile mammals.
Their whiskers contain nerve fibers, which make them
sensitive. They may use their whiskers to aid in navigation
or to detect vibrations from prey in the water.
How do sea lions sleep?
On land, sea lions will sleep in a variety of positions,
often on top of their friends. California sea lions have
been seen interacting with other species of pinnipeds,
such as northern elephant seals, harbor seals, Northern
fur seals, and Steller sea lions. In the water, they
will sink to the bottom of shallow areas, and occasionally
rise to the surface for air. In deeper water, they will
float upright with the tip of their nose out of the water.
How do sea lions regulate their body temperature?
Sea lions have the ability to regulate their own body
temperature. They can often be seen floating with one
flipper out of the water. The reason for this is because
the capillaries are close to the surface of the skin
and can catch sunbeams to warm their body. To cool down,
they put their flipper into the water then raise it back
up into the air which cools them off during the evaporation
process. This process is called thermoregulation..
Do sea lions molt?
Sea lions molt once each year, usually after the breeding
season, but not as obviously as true seals. Molting is
when an animal loses its fur or feathers and the coat
is replaced with a new one. During the molting season,
seals cannot enter the water because they do not have
proper insulation to keep them warm. Therefore, they
fast during this time period. Sea lions are able to enter
the water during their gradual molting period. Sea lion
pups will molt twice during their first six months of
life. Have you ever touched a sea lion? They are soft
and, when wet, feel like a dog that just went swimming.
How do sea lions scratch?
Sea lions actually have three toe nails on each hind
flipper. Because sea lions are so flexible, they can
reach almost all their possible itchy spots. Sometimes
they rub against rocks or other sea lions. Seals have
nails on both their front and hind flippers.
How large are sea lions?
Females tend to average between 200 and 400 pounds
(90 - 180 kg) in weight, with a length between 5 and
6.5 feet (1.5 - 2 m). Pups only weigh about 13 pounds
(6 kg) and are 2.5 feet (75 cm) long when born. Males
tend to be larger, weighing about 600 to 800 pounds (270
- 360 kg), with a length of 6.5 to 8 feet (2 - 2.4 m).
There are records of adult male sea lions reaching 1,000
pounds! Their cousin, the walrus, makes California sea
lions look small. Walruses may weigh more than 3,500
pounds (1,600 kg). Wow, that sure is big!
How long can a sea lion hold its breath?
Sea lions can remain underwater for an average of 8
to 20 minutes. Unlike dolphins, sea lions exhale before
diving. Naturally, their nostrils are closed, but they
have special muscles to open them in order to breathe.
Sea lions can dive to depths between 450 and 900 feet
(135 - 272 m). The reason they can dive so deeply and
stay underwater so long is because they have a high tolerance
for carbon dioxide. The oxygen in their body concentrates
in their heart and central nervous system rather than
in non-vital organs. Their relative, the elephant seal,
can hold its breath for 62 minutes and dive to depths
of 4,100 feet (1240 m).
Where do California sea lions live?
The majority of California sea lions live in California,
but the population range extends from Vancouver Island,
British Columbia, to Mexico.
Do the sea lions at DRC take vitamins?
Both of DRC’s sea lions take vitamins orally
each day. The fish they receive are flash-frozen from
the north Atlantic and lose nutrients during the freezing
process. To compensate, the sea lions’ fish diet
is supplemented with vitamins such as B Complex and C
Plus. Just like
dogs, DRC’s sea lions
also receive Nemacide, a medication to prevent heartworms.
Being in and out of the water makes sea lions susceptible
to a variety of internal parasites. This is also a
concern for wild sea lions.
Do California sea lions have predators?
Great white, hammerhead and blue sharks, as well as
killer whales, occasionally hunt sea lions. Young sea
lions are often vulnerable to predation due to unfamiliarity
with their new water environment. Water pollution, as
well as marine debris such as fishing line, also endangers
our friends of the sea. Ropes can tangle around the necks
of marine mammals and cut into their skin, blocking the
passage for food and eventually resulting in starvation.
During the late 1800s and early 1900s, sea lions were
hunted and harvested for their blubber and fur. Sea lions
are now protected under the Marine Mammal Protection
Act of 1972.
Breeding
Once a sea lion becomes sexually mature, at around
age four or five, they are able to breed. Female sea
lions are called cows, while males are called bulls.
Those who live in Baja, California and southern California
establish breeding territories from May through July.
Cows congregate in closely packed, moderate to large
groups. Bulls defend territories and fast during the
breeding season.
Males compete for dominance, leaving the younger males
without a chance to mate for the season. One distinct
characteristic of a full-grown breeding male is the presence
of a sagittal crest, a raised forehead that appears at
about 10 years of age. The dominant male will mate with
an average of 16 females in one season. Once the egg
is fertilized inside the female, she can delay implantation
of the egg to stop the embryo from growing. The delayed
implantation may last up to three months with an average
gestation period lasting 9 months. Sea lions mate approximately
20 - 30 days after the birth of their pup, leaving only
about one month out of the entire year that she is not
pregnant.
In the Northern Hemisphere, pups tend to be born in
mid-June. Each mother usually gives birth to a single
pup. Twins are rare and mothers seldom adopt other pups.
The pup nurses from the mother's four abdominal teats
for about 6 - 12 months. The length of lactation increases
with the increasing age of the female. Sea lion milk
contains about 35% fat so the pups grow rapidly. Pups
begin feeding on fish along with the mother's milk after
about two months. Between nursings the mother returns
to the sea and feeds for several days, leaving her pup
on the mainland. Upon her return, she recognizes her
pup on land through vocalizations and/or scent. Once
the mating season is over, the males seasonally migrate
long distances north while the females do not move beyond
the Southern California Channel Islands. The males return
to the breeding grounds from March to May.
REFERENCES:
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rosmarus divergens
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Inc., New York, NY.
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Information Can Be Used with Proper Citing
Dolphin Research Center, 58901 Overseas Highway, Grassy Key, FL 33050-6019
305-289-1121 www.dolphins.org
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