How long do nurse sharks sleep?

Basedd on my experienes in Eleuthera, Bahamas, nurse sharks actually do nap, breathing regularly and without moving, which most shaks cannot do; they have to be moving to get enough water through their gills. Nurses can breathe stationary because they can pum water through their mouth and out their gills. Nurse sharks generally dont have a sleep period like we do, they dont have a long period of REM sleep, which is when you are in a deep sleep state. Nurse sharks generally nap for around an average of 1 hour, but sometimes 2, and 3 hours as well. Nurse sharks will nap either on the sea floor (in my case, in a small bay area, 20 feet deep) or in their shallow nests. Nurse sharks are generally nocturnal animals, which is why the often nap in the day.