Female seals follow highly synchronised breeding seasons. They can control the development of the embryo, and put it on hold if necessary, until conditions are perfect for giving birth.

What’s in here Seal   © ColdNightMist

Seals and sea lions spend most of their lives at sea. They come to shore once a year for two reasons: to give birth and to mate.
They even return to the same breeding location each year around the same time. Sea lion females arrive on the beach a week or two after the males have settled and established their territories. At that stage they are pregnant with the young conceived a year earlier to which they will give birth a few days later. Soon after that they become sexually receptive again and are pounced upon by a dominant male.
Each female above the age of three usually give birth to one pup each season, which they will feed, protect and nurse until it is ready to spend the rest of the year out in the open ocean. They will travel with the rest of the pack until it is time to return to the beach where they were born for the next breeding season.

The normal gestational period for a seal is about eight months. If a mother seal were compelled to give birth eight months after conception, her cub would be born at sea and soon die from cold, drowning, or being eaten. By delaying implantation for a couple of months, mother seals can time the birth of their young for a scheduled landing, ensuring the safety of the next generation.

This phenomenon is known as “delayed implantation,” or “embryonic diapause”: an embryo is formed, yet isn’t implanted in the mother’s uterus. And not until it is implanted can the embryo gain access to the resources it needs to grow and develop.

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