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Why do harp seals give birth on seasonal pack ice?

Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.
A mother harp seal and a young “whitecoat.” Adult harp seals are gray with black spots. Young harp seals are called “whitecoats,” “bedlamers,” “beaters,” or “graybacks,” depending on their age.
harp seal A mother harp seal and a young “whitecoat.” Adult harp seals are gray with black spots. Young harp seals are called “whitecoats,” “bedlamers,” “beaters,” or “graybacks,” depending on their age.

Harp seals give birth on seasonal pack ice because it serves as a necessary whelping platform for their young.1

To ensure that birth occurs when this ice is available, harp seals utilize a biological process known as delayed implantation. After fertilization, the egg develops into a blastocyst that floats freely in the uterus for four months before implanting. This mechanism extends the total gestation period to 11.5 months, effectively synchronizing the arrival of the pups with the seasonal presence of the ice floes.1