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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.
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