Researchers have learned a lot about the social life of whales, including this sleeping behavior of sperm whales. Dr. Patrick Miller reported how groups hang out vertically just below the surface in 2008; see a summary of why it’s considered sleeping and a video of some being nudged awake.
As far as I know, this is a unique pattern, not seen in other whales. Social patterns seen in other whales usually are about feeding, breeding, and migration.
Toothed and Baleen
My trusty Audobon Guide to Marine Mammals, reminded me by its very organization that the two major types of whales are based on how they feed. The ‘toothed’ whales, including sperm whales and Orcas, eat large fish and mammals while ‘baleen’ whales, including blue, humpback, and grey whales, filter feed on small prey.
In general, the toothed whales have more complex and stable social groupings. Specifically, sperm whales and Orcas have female-based groups that are life-long and hang out and hunt together. Baleen whales tend to be more solitary, like the blue whale. Some, like humpbacks and grey whales, will form temporary groupings for feeding and breeding.
The humpbacks have developed a bubble net form of feeding that requires impressive timing and coordination.
One of the grey whales’ well-known nurseries in San Ignacio, Mexico, is a world famous gathering where birthing mothers hang out with each other as well as with humans.