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V. Adaptations for an Aquatic Environment.
A. Swimming.
1. Sea turtles are strong swimmers. The cruising speed for green sea turtles is about 1.5 to 2.3 kph (0.9-1.4 mph). Leatherbacks have been recorded at speeds of 1.5 to 9.3 kph (0.9-5.8 mph).
2. Forelimbs are modified into long, paddle-like flippers for swimming.
3. Neck and limbs are nonretractile. The shell adaptations necessary for retractile extremities would impede rapid swimming.
A sea turtle swims with powerful winglikes beats of its foreflippers.
B. Diving.
1. Sea turtles are excellent divers. Leatherbacks routinely dive more than 305 m (1,000 ft.), and they may reach depths of more than 1,190 m (3,900 ft.) seeking jellyfish.
2. Since they are ectothermic, sea turtles have a slow metabolic rate. This slowed metabolism allows them to stay submerged for long periods of time.
a. Hawksbill turtles have been known to remain submerged for 35 to 45 minutes.
b. Green sea turtles can stay under water for as long as five hours. Their heart rate slows to conserve oxygen: nine minutes may elapse between heartbeats.
c. In the north-central Gulf of California, black sea turtles return each year to specific areas. They bury themselves under water in sand or mud and may remain dormant from November to March.
3. During long dives, blood is shunted away from tissues tolerant of low oxygen levels toward the heart, brain, and central nervous system.
4. Leatherbacks have high concentrations of red blood cells; therefore, they can retain more oxygen. The muscle of leatherbacks has a high content of the oxygen-binding protein myoglobin. Myoglobin transports and stores oxygen in muscle tissue.
C. Respiration.
In studies conducted on green sea turtles, lung capacity exchange in one breath exceeded 50%.
D. Salt secretion.
1. Sea turtles can live in seawater with no need for a freshwater source. They obtain sufficient water from their diet and from metabolizing seawater.
2. Like other marine reptiles and seabirds, sea turtles have a salt gland to rid their bodies of excess salt. This gland empties in the sea turtles' eyes. The secretion of salt and fluid makes them look as if they are "crying" when they come ashore. These "tears" help keep the eyes free of sand while females dig their nests.
E. Sea turtles on land.
1. For the most part, the only time sea turtles need to leave the sea is when females haul out to lay eggs; however, on uninhabited or sparsely-inhabited beaches, turtles have been observed basking on land.
2. Many adaptations that make sea turtles successful in the sea make them slow and vulnerable on land.
