Sea turtles, despite spending most of their lives in the ocean, cannot breathe underwater. They are reptiles, similar to humans, meaning they possess lungs and must come to the surface to inhale air. This fundamental biological requirement distinguishes them from fish, which use gills to extract dissolved oxygen directly from water.
How Sea Turtles Breathe
Sea turtles breathe air using their lungs, which are located beneath their upper shell (carapace). Unlike mammals, sea turtles do not have a diaphragm; instead, they use muscles attached to their pelvic and shoulder girdles, and to their lower shell (plastron), to expand and contract their lungs. This allows them to take in oxygen and expel carbon dioxide.
How Long Sea Turtles Stay Underwater
Sea turtles exhibit an impressive ability to remain submerged for extended periods. The duration of their dives varies significantly based on their activity level and environmental conditions. When actively foraging or escaping predators, sea turtles typically dive for 20 to 40 minutes. However, during periods of rest or sleep, they can hold their breath for several hours, often ranging from 4 to 7 hours.
Factors such as water temperature, species, and age also influence dive duration. Some species in cold water can remain underwater for much longer, potentially for days or even months during hibernation-like states.
Physiological Dive Adaptations
Sea turtles have physiological adaptations for prolonged underwater dives. One such adaptation is bradycardia, where their heart rate significantly slows down during a dive, sometimes to as little as one beat per minute. This reduction in heart rate helps conserve oxygen by decreasing its consumption.
They also have peripheral vasoconstriction, redirecting blood flow away from non-essential organs and tissues. This ensures that oxygen is prioritized for the brain, heart, and central nervous system, which are crucial for survival. Sea turtles also have a high oxygen storage capacity due to elevated concentrations of hemoglobin in their blood and myoglobin in their muscles. Myoglobin specifically allows muscles to store a significant amount of oxygen for use during dives.
Sea turtles can tolerate higher levels of lactic acid buildup from anaerobic respiration. This process generates energy without oxygen, acting as a backup system during prolonged dives when oxygen becomes scarce. Their metabolic rate also decreases, particularly during resting periods, which further reduces oxygen demand and allows for longer submersion times.
Why Sea Turtles Must Surface
Despite their remarkable adaptations for underwater endurance, sea turtles must ultimately return to the surface to breathe. Their physiological mechanisms, while highly effective, are temporary solutions to cope with oxygen deprivation. The need for atmospheric oxygen is absolute, as their lungs are designed for air breathing, not extracting oxygen from water.
If a sea turtle is prevented from reaching the surface, such as by entanglement in fishing gear or entrapment, it can quickly deplete its oxygen stores. A stressed turtle will use oxygen rapidly, leading to drowning within minutes if it cannot access air. This dependency on surface air underscores their vulnerability to human activities and environmental hazards in their marine habitats.