Seals evolved from land mammals, so their
reproductive activities happen on land (or ice).
There are several species of seal, but the general
process is about the same. During the seal
breeding season, mature males fight to claim
territory on the breeding beaches. These fights
are dangerous and take a lot of energy. The
winning “beachmaster” has to protect the territory
that he wins, so he doesn’t get to go fishing. He
has to live off his fat. All of this tends to
shorten his life. Male seals are much larger than
females because small males don’t get much chance
to pass on their DNA.
The females give birth on the beach and nurse
their pups. After about 6 weeks, the females’
bodies are ready to become pregnant again. They
will mate with whatever male has claimed the
beach. This will give her pups “winning” genes.
She might also mate with a male who is able to
sneak onto the beach. That way, even if the
beachmaster is not fertile, she can still get
pregnant. (The seals don’t “know” any of this
stuff, but that’s what happens).
Seals are mammals, so fertilization happens
inside the female. Male seals keep their
reproductive parts tucked away inside their bodies
until they need them. This keeps their
streamlined shape in the water. Once an egg is
fertilized, it only divides a few times, then
stops for months. This way, pups are born when
there is plenty of food around when the mothers
need to make milk, which takes a lot of energy and
nutrients. The mothers may live off of fat or go
hunting and leave the babies on shore.
Why do you think mother seals only have one pup
If you are interested in questions like this,
you may want to study mammalogy or marine biology.
Thanks for asking,