Turtles are air-breathing reptiles, yet they possess a remarkable ability to remain submerged underwater for extended periods, which varies significantly based on activity, environment, and species. This aquatic endurance is made possible by unique physiological and anatomical adaptations. While they must eventually surface to breathe air with their lungs, the duration they can delay this necessity ranges from mere minutes to several months.
Active vs. Resting Submersion Times
The time a turtle can remain underwater is directly proportional to its level of physical activity. When a turtle is actively swimming, foraging for food, or attempting to evade a predator, its oxygen consumption rate increases dramatically. During these periods of high activity, submersion times are relatively short, typically lasting only a few minutes or up to an hour for large sea turtles like the leatherback.
When a turtle is resting, sleeping, or in a state of dormancy, its body enters an energy-saving mode. This extended duration is a consequence of a significantly lowered metabolic rate, which drastically reduces the demand for stored oxygen. Sea turtles, for example, can rest on the seafloor and stay submerged for four to seven hours. Freshwater turtles also exhibit this pattern, with active dives being much shorter than resting periods where they can remain underwater for an hour or more.
Physiological Adaptations for Oxygen Deprivation
Turtles have evolved mechanisms that allow them to conserve oxygen and tolerate environments with low or no oxygen, a state known as anoxia. One effective strategy is metabolic suppression, which is the ability to drastically slow down the body’s energy consumption. This reduction in metabolic rate, sometimes to as low as 10–20% of the normal resting rate, slows the depletion of oxygen stores.
A related mechanism is bradycardia, or the significant reduction of the heart rate during a dive. For instance, a green sea turtle’s heart rate can slow so much that nine minutes may elapse between heartbeats. This effectively shunts blood flow away from tissues tolerant of low oxygen toward the brain and central nervous system. Also, some sea turtles, such as the leatherback, have a high concentration of the oxygen-binding protein myoglobin in their muscles, which acts as an additional oxygen reserve to fuel muscular activity during long dives.
When stored oxygen is depleted, turtles can temporarily switch to anaerobic respiration, a process that produces energy without oxygen. This process generates lactic acid, a metabolic byproduct that can quickly become toxic in high concentrations. Turtles counter this acidosis by exploiting the buffering capacity of their shell and skeleton, which releases carbonate buffers to neutralize the accumulated lactic acid. This tolerance allows species like the painted turtle to survive for months in an anoxic environment at low temperatures.
The Role of Environment and Species
Temperature is a major factor that modulates a turtle’s breath-holding capability due to their ectothermic nature. As cold-blooded animals, a turtle’s body temperature and metabolism are directly influenced by the surrounding water temperature. Colder water drastically slows the metabolic rate, which in turn reduces the need for oxygen.
This principle is demonstrated during winter brumation, where freshwater species enter a state of dormancy in cold, often ice-covered, ponds. During this time, the turtle’s metabolism is reduced to a bare minimum, allowing them to remain submerged for weeks or even months without surfacing for air. The optimal temperature for this long-term, anoxia-tolerant submergence is around 3 degrees Celsius for some species.
Many freshwater turtles rely on non-pulmonary, or “aquatic respiration,” during prolonged submergence. This involves absorbing dissolved oxygen directly from the water across highly vascularized surfaces, such as the lining of the throat or the cloacal region. This process, known as cloacal respiration, is not a replacement for lung breathing, but it allows species like the Mary River turtle to extend their submersion time by diffusing small amounts of oxygen through these tissues while resting.