Harbor seals can sleep underwater. Their nervous system has an automatic shut-off mechanism that prevents them from breathing at inappropriate times. They will surface subconsciously to breathe.
Harbor seals can detect prey using nerves in their whiskers that sense pressure changes in the water.
A harbor seal’s hearing is almost 14 times greater under water
Harbor seals have large eyes that are protected by oily “tears” which help the seal see in deep, dark waters.