|
Deepseawaters
Home Deepsea
Animals
Northern Elephant Seal
Northern Elephant Seal
Common Name: Northern
Elephant Seal
Scientific Name: Mirounga angustirostris
Meaning of Scientific Name: Having a Narrower Snout than the
Southern Elephant Seal
History
Hundreds of thousands of northern
elephant seals once inhabited the Pacific Ocean.
They were slaughtered wholesale in the 1800s for the oil that
could be rendered from their blubber. By 1892, only 50 to
100 individuals were left. The only remaining colony was on
the Guadalupe Island off the coast of Baja California.
In 1922, the Mexican government gave protected
status to elephant seals, and the U. S. government
followed suit a few years later when the seals began to appear
in Southern California waters. Since that time, elephant seals
have continued to multiply exponentially, and they have extended
their breeding range as far north as Point Reyes. Today, there
are approximately 160,000 northern elephant seals.
The first elephant seals on Año Nuevo
Island were sighted in 1955, and the first pup was born there
in 1961. In 1978, 872 were born there. Males began to haul
out on the mainland in 1965. A pup born in January 1975 was
the first known mainland birth of a northern elephant seal
at Año Nuevo; 86 pups were born there in 1978. By 1988/1989,
about 2,000 elephant seals came ashore at
Año Nuevo, and the number of seals breeding and giving
birth on the mainland is still increasing. During the 1994-95
breeding season, approximately 2,000 pups were born on the
mainland.
Description
Northern elephant seals
are in the family Phocidae. They have short,
coarse grey or brown fur and a very thick blubber layer that
insulates them from cold water.
Adult males are larger than females and can
weigh up to 5,000 pounds. Females can weigh up to 1,700 pounds.
Adult males have a ‘chest shield' that
develops with age to protect them from injury when they fight
with other males for breeding territories. The chest shield
is pink and is formed from keratinized skin. Males also develop
a probosicis with age.
Once each year, northern elephant
seals molt. An epidermal molt is a unique characteristic
of elephant seals and monk seals.
Once a year the animals come ashore and shed their fur and
the first layer of skin (or epidermis). The skin and fur come
off in sheets as new skin and fur replace old. When the molt
is finished, the animals have silver fur. Between the molting
and breeding seasons, northern elephant seals remain at sea
for 6 to 8 months, traveling thousands of miles and spending
86% of their time submerged
Habitat and Range
Breeding colonies are found primarily along
the California coast. In spring and summer seals also haul
out at these areas for molting, as well as at some sites in
Washington and British Columbia. Outside of the breeding and
molting seasons, for roughly 8 to 10 months of the year, Northern
Elephant Seals range widely to forage into the eastern
and central North Pacific. Vagrant juveniles have been sighted
as far away as Hawaii and Japan.
Feeding
They are nocturnal deep pelagic feeders. At sea, elephant seals typically
dive 20 minutes to a depth of 1,000 to 2,000 feet in search
of food: rays, skates, rat fish, squid, and small sharks,
Octopus, hagfish. The maximum recorded depth is 5,015
feet by a male in 1991.
The females eat nothing while they are giving birth, nursing,
and mating, and the males go without food for up to three
months at that time. They are preyed upon by killer whales
and sharks.
Behaviour
During the breeding and molt seasons Northern
Elephant Seals may aggregate in groups of up to several
hundred. When ashore to molt, they crowd together in dense
groups and spend most of the time sleeping. The rest of the
year they travel or forage at sea and are thought to be solitary.
Breeding Seson
The elephant seal breeding
season begins at Aņo Nuevo in December, when the first males
arrive. From fourteen to sixteen feet long and weighing up
to 2 1/2 tons, these huge bulls engage in violent battles
to establish dominance. The successful bulls do much of the
breeding, with most of the duty falling on the "alpha" bull
at the top of the social ladder.
Birth
In late December, the females begin to arrive
and form "harems" on the beaches of the Reserve. Much smaller
than the males, they average ten to twelve feet in length
and weigh 1,200 to 2,000 pounds. Three to six days after she
arrives, the female gives birth to the pup that was conceived
the previous year. Normally only one pup is born to each female,
and she nurses for 25 to 28 days.
Nursing
Ordinarily, a mother nurses her own pup,
although if they are separated another female may adopt the
youngster. Feeding on its mother's rich milk (55% fat), the
pup grows from approximately 75 pounds at birth to 250-350
pounds in less than a month. Some resourceful pups nurse from
two or three females. They can weigh 600 pounds and are aptly
called "super weaners".
Mating and Gestation
 Females
come into season and mate about 24 days after giving birth.
However, the fertilized egg does not implant in the wall of
her uterus for about four months a rare phenomenon called
"delayed implantation". The theory is that
the female is so weak after nursing and fasting that she doesn't
have enough energy to nourish the egg. Since the seals' gestation
period is seven months, this delay means that the young will
be born after the female reaches her breeding ground the following
year. The pups could not survive if born at sea. Adult females
may mate several times before returning to the ocean, abruptly
weaning their pups by desertion. By mid-March, most of the
adult seals are gone, leaving the pups behind.
Weaners
When the weaned pups are four to six weeks
old, their original coat of black fur molts and is replaced
by a shiny new silver coat. Soon afterward, they begin learning
to swim in the shallow offshore waters or ponds formed by
rainwater. They are very curious and rather awkward and somewhat
afraid of the water at first. But they learn quickly, spend
more and more time swimming about, and then, during the last
three weeks of April, they go to sea one by one and disperse
northwestward. They feed off the coast of northern Washington
and Vancouver Island in British Columbia and do not appear
on land again until September.
Molting
Pinnipeds, like other mammals, must replace
old skin and hair. Most animals shed hairs year-around, but
elephant seals do it all at once. The molting
process is so abrupt in the elephant seal that it is called
a catastrophic molt. During the spring and
summer months, elephant seals return to Aņo
Nuevo for their annual molts.
* April to May - Females and juveniles
* May to June - Sub-adult males
* July to August - Adult males
The Secret Lives of Elephant Seals
Northern elephant seals
are mysterious and unique creatures. Elephant seals range
from Mexico to Alaska and Hawaii in search of food and spend
80 percent of their life in the open sea. Not only do they
spend most of their life in the ocean, 90 percent of that
time is spent underwater: eating, sleeping, digesting, and
traveling. They are built to survive continuous dives to depths
that would squeeze the life out of any other mammal. The average
dive reaches 1,000 to 2,000 feet, lasts close to half an hour
and is followed by only 3-5 minutes at the surface to breathe.
Why do they dive so deep?
The oceans are full of food for millions
of animals, but relatively few feed at the depths elephant
seals prefer. As a result, they face little competition for
food. Feeding in almost total darkness, elephant seals
use their large eyes and the bioluminescence of some prey,
such as octopus and squid, to find food where
other predators would not even be able to see. They may use
their stiff yet sensitive three to eight inch long whiskers
to "feel" some food, such as Pacific hake, skates, rays,
shrimp, small sharks and crabs.
Threats
Disease, pollution, loss of habitat, oil
spills, entanglement in derelict fishing nets, and human disturbance;
predation by great white sharks and
killer whales.
 Email To Friend
| 
