A beautiful aerial video has emerged of a grey whale swimming on its back off the shore of Los Angeles, CA, USA.

The footage, shot on Sunday, captures the strange behaviour displayed by the migrating marine mammal.

"Very strange behavior of a gray whale that turns upside down between every breath as its companion dives deep in between breaths," the filmer, Mark Girardeau noted online.

"Pacific gray whales migrate South to Mexico to give birth and then migrate back up to Alaska to feed," he added.