Sea turtles are air-breathing reptiles that must regularly return to the surface for oxygen, despite spending almost their entire lives submerged. Unlike fish, they lack gills to extract oxygen directly from water. Surfacing is an unavoidable behavior for their survival.
How Sea Turtles Breathe
Sea turtles possess well-developed lungs, similar to those of mammals, for gas exchange. These lungs are positioned beneath their carapace, the upper part of their shell. Unlike terrestrial turtles, sea turtles have respiratory adaptations enabling rapid gas exchange when they surface. Their lung capacity exchange per breath can range from 27% to 80%, significantly higher than land reptiles, allowing them to quickly replenish oxygen and expel carbon dioxide.
Breathing involves muscle movements connected to their pelvic and shoulder girdles, and their plastron, the lower part of their shell. Turtles may “rock” their shoulders when not submerged, a movement aiding lung ventilation. Underwater, sea turtles close their nostrils to prevent water entry.
Remarkable Breath-Holding Abilities
Sea turtles exhibit impressive breath-holding capabilities, varying with activity and environmental conditions. While active, they typically surface every few minutes, holding their breath for 4 to 7 minutes. During rest or sleep, they can remain submerged for 4 to 7 hours. In colder winter waters, some species, like loggerheads, can extend dive times up to 7 hours.
Several physiological adaptations contribute to extended dive times. Sea turtles possess a slower metabolic rate compared to mammals, reducing oxygen consumption. They can decrease their heart rate (bradycardia) to conserve oxygen during dives; a sea turtle’s heart rate can slow to one beat every nine minutes. Their blood has high hemoglobin concentrations, and their muscles contain high myoglobin levels. These proteins store and transport oxygen, allowing them to store significant oxygen in blood and tissues, which is then distributed to organs like the heart and brain during long dives.
Why Surfacing is Critical
Despite remarkable underwater adaptations, surfacing for air remains vital for sea turtles. Their inability to reach the surface leads to drowning. This vulnerability makes them susceptible to human-induced threats. Accidental capture in fishing gear, such as trawls and gillnets, is a significant danger, as entangled turtles cannot ascend to breathe. An estimated 1.5 million sea turtles were incidentally caught in fisheries globally over an 18-year period.
Vessel strikes pose another serious risk, particularly when turtles are at or near the surface to breathe, bask, or feed. They often cannot react quickly enough to approaching boats.
Coastal development and artificial lighting near nesting beaches can disorient hatchlings, drawing them away from the ocean. This increases their risk of exhaustion, dehydration, or predation before they can reach the water and take their first breaths. Without consistent access to the surface, sea turtles cannot survive.