Dolphins:
1. Unihemispheric Sleep: Dolphins can enter a unique sleep state called unihemispheric sleep, where only one hemisphere of their brain sleeps while the other remains awake. This allows them to maintain partial awareness of their surroundings and quickly respond to potential threats or social interactions.
2. Slow-Wave Sleep: Dolphins also experience periods of slow-wave sleep, similar to humans. During this phase, both hemispheres of their brain are asleep, and they exhibit reduced muscle activity and slower breathing.
3. Resting Behavior: Dolphins typically rest near the water's surface, often engaging in "logging" behavior. They float passively, keeping their blowhole above water for breathing.
Sharks:
1. Brief Sleep Periods: Sharks generally have short and infrequent sleep periods. Unlike mammals, they do not have distinct sleep cycles or REM sleep. Instead, they enter short periods of rest or "behavioral quiescence."
2. Immobile Rest: Some shark species, such as nurse sharks, may rest by lying motionless on the ocean floor or among coral reefs. During this time, their metabolic rate slows down, and their breathing becomes shallow.
3. Swimming Rest: Other shark species, like the whale shark, may continue swimming slowly while resting. They maintain a reduced level of activity and lowered metabolic rate but remain partially alert.
4. Periodic Breathing: During rest, sharks often exhibit periodic breathing patterns. They may pause between breaths for longer intervals than when actively swimming.
It's important to note that different dolphin and shark species may have variations in their sleeping behavior, and ongoing research continues to provide more insights into their unique sleep patterns.