Female southern elephant seals reach sexual maturity between 3 - 6 years
of age, giving birth to only one pup annually, although some have been
observed nursing 2 pups (in this case adoption is supposed). Males reach
sexual maturity between 4 - 5 years of age but generally don’t reproduce
until about 10 years of age.
Large males come ashore around August to start to form their territories
in which they will have their harem.
Elephant seals have a
polygynous
mating system, with a successful male mating with numerous females in
one season.
Only 2% - 3% of males are successful, winning "breeding rights", forming
in this way harems containing more than 100 females in some cases
(normally 10 - 15 females per harem).
Females give birth in September - November in the first 10 days after
coming ashore. The mother does not return to sea until the end of the
lactation, which last about 19 – 25 days. During this period, she lives
on her blubber generally losing about 35% of her body weight, or up to
8kg per day. Pups are born with dark brown-black fur, which they will
moult, after they are weaned, for a shorter coat of grey hair. They
measure about 1,2 – 1,3m and weigh 30 - 40kg when born. During
lactation, pups grow about 4kg per day, obtaining 120 - 160kg and a size
of about 1,80m by the time they are weaned.
Females mate between 3 - 5 days before their pup is weaned. They leave
the beaches fertilized, but due to the phenomena of ‘delayed
implantation’ their actual gestation period starts around 2 - 3 months
later, allowing them to recuperate energy levels. This phenomena is
common for many pinniped species.
After lactation, when the females leave their pups and return to sea to
feed, pups stay alone on the beach and depend on their energy reserves
(obtained by the mother milk) to survive. After 6 - 8 weeks, during
which they loose around 1kg per day, they leave the breeding ground to
feed at sea. Pup mortality can be high. It is estimated that between 40% - 50%
of the pups born in one season do not reach 1 year of age.
Adult males do not feed during the breeding season
and can lose more than 40% of their body weight or
12
kg per day. The amount of time spent ashore by males during the breeding
season varies greatly, ranging from 60 to 90 days (females typically
spend about 1 month onshore).
After breeding season, elephant seals enter in a feeding period, where
they try to recuperate the weight they lost during reproduction and
generate reserves for their following season on land: the moult, which
last around 30 - 40 days. After the moult, they return again to the sea
where they recuperate and prepare for the next season on land, the
breeding season.
This way, the elephant seal complete their annual season of 2
terrestrial phases and 2 marine phases.
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