This is probably one of the main reasons why they hunt in groups. It takes the coordination of several individuals to capture a dolphin that can swim much faster than they can. We are more likely to see whales during the day, simply because we cannot observe them easily without the light of the sun. But whales come to the surface to breathe during the day and during the night. A colleague of ours is studying gray whales that migrate along the coast of California using such a device to see if the whales continue to travel during the night, or if they stop to rest.
Some whales float at the surface for a while after they die.
Over the years I have seen a few sperm whales and a blue whale once, just lying on their sides peaceably at the surface. They eventually sink to the bottom where most whales end up. There, scavengers such as crabs, fish and bacteria feast. It is interesting to think that the largest animal in the world, the blue whale, ends up starting all over again as the smallest of living things, bacteria. Some whales, very few actually, wash up on beaches after they die.