Sea turtles, despite their aquatic lives, are reptiles that breathe air using lungs, not gills like fish. This means they must regularly return to the surface to inhale oxygen and exhale carbon dioxide. This need for air shapes much of their behavior and physiology in the marine environment.
How Sea Turtles Breathe
Sea turtles possess fully developed lungs. They exchange gases at the ocean’s surface, taking a breath of air before submerging. Their respiratory system is highly efficient, designed to maximize oxygen uptake during these brief surface intervals. Their large lung volume and tidal volume promote rapid gas exchange, allowing them to quickly replenish oxygen stores before diving again.
When a sea turtle surfaces, it typically takes a series of quick, deep breaths. This efficient process allows them to acquire enough oxygen to sustain themselves during their underwater excursions. Their lung structure and respiratory muscles enable them to exchange a high percentage of gases with each breath, optimizing surface time.
Underwater Endurance and Adaptations
Despite needing air, sea turtles have physiological adaptations that allow them to remain submerged for extended periods. One adaptation is bradycardia, where their heart rate significantly slows during a dive, sometimes dropping by 40-60% and even reaching as low as two beats per minute. This reduction conserves oxygen by slowing its delivery to tissues.
Sea turtles also use peripheral vasoconstriction, redirecting blood flow to essential organs like the brain and heart, while reducing it to less oxygen-sensitive areas. Their blood and muscles have an enhanced capacity to store oxygen, thanks to high concentrations of hemoglobin and myoglobin. Leatherback sea turtles, for instance, have a blood oxygen-carrying capacity twice that of smaller species. In extreme oxygen scarcity, sea turtles can temporarily switch to anaerobic respiration, a less efficient process that allows muscles to function without oxygen, though it causes lactic acid buildup.
Factors Affecting Dive Duration
The duration a sea turtle can stay underwater is influenced by several factors. Activity level plays a significant role; a resting turtle can remain submerged far longer than one actively swimming, foraging, or fleeing a predator. For green sea turtles, routine dives typically last 4-7 minutes, but resting dives can average around 18.5 minutes and range up to 44.8 minutes.
Water temperature affects dive duration; colder water slows metabolism, reducing oxygen consumption and allowing for longer dives, while warmer water increases metabolic rate, shortening dive times. During winter hibernation, some sea turtles can hold their breath for up to 7 hours. Different species also exhibit varying breath-holding capacities; leatherback sea turtles, for example, can hold their breath for up to 85 minutes. Larger and older turtles typically endure longer dives than younger, smaller individuals due to greater oxygen reserves and lower metabolic rates. Stress, such as entanglement in fishing gear, drastically increases oxygen consumption, severely limiting dive time and risking drowning.