Voyage of the Turtle: Part II Physiology

While I’ve shared how the Voyage of the Turtle: in the Pursuit of the World’s Last Dinosaur took a broad-focused, holistic sweep of the world between humans and leatherbacks, it also tackled specifics of sea turtle’s physiology.

Diving physiology is intricate and poorly understood. Considering that humans dwell on land and most animals that we have basic knowledge of also dwell on land, it can be hard to imagine let alone study something that lives almost strictly below water—something that, as an individual, will swim across an entire ocean on a regular basis and breathe every 10 minutes or so and females nest every few years.

SafinaCover

When turtles get caught in fishing lines, they don’t get to surface in the next 10 minutes. Or 20. If they are reeled in after 50 minutes they will have high acid levels in their blood and require roughly 24 hours to fully recuperate and perhaps an hour of it spent hyperventilating. This has role in how turtles drown when law requires fisherman to toss turtles immediately back into the water instead of resting aboard. If the animal is submerged for an hour and a half they will cease to have any oxygen in their blood.

While diving they may not return to the surface for an hour, though other turtles like loggerheads and greens can hibernate on the ocean floor for weeks.

Deep Divers:

  • Emperor penguins: 455 meters/1500 feet
  • Some seals: 915 meters/3000 feet
  • Sperm whales: 1130 meters/3700 feet
  • Leatherbacks: 1190 meters/3900 feet

Diving to these depths means that leatherbacks can withstand 120 atmospheres of pressure (1 atmosphere being the air pressure at sea level) or 1800 psi (15 psi for air at sea level).

Humans have the capacity to store oxygen in their lungs and in a single breath intake 10 percent of that capacity. Turtles have the capacity to store oxygen the normal way through lungs with 80 percent in a single inhalation, but then they have a back up system for dives because they must displace all that oxygen from their lungs so the lung buoyancy can’t prevent them from sinking to great depths.

When a leatherback dives, the lungs collapse about 90 meters (300 feet) down. Air leaves the lungs and enter the cartilage-enforced trachea. This action prevents compressed oxygen from entering the bloodstream, which would otherwise expand upon the return journey and cause a condition many know as the bends. After entering the trachea but before reaching critical depths, the oxygen dissolves and enters into the blood and organ and muscle tissue. This ability also explains why the animals have small lungs and large hearts for their body size.

Peeking Turtle

Leatherback sea turtle peeking above the waves. Photo courtesy of Florida Fish and Wildlife Commission Research Institute (website and Flickr stream).

Large animals like whales dive deep simply because they have more blood. However, both whales and leatherbacks make use of their massive size yet small surface area to tolerate the cold at such depths.

Another unique feature in diving animals, turtles and mammalian specimens alike, is the ability to survive with an altered brain metabolism. Most animals can tolerate low levels of oxygen in the skeletal muscles (that’s how we get the lactic acid burn from exercising), but only diving specialists can decrease how much oxygen their brain can run on. Specially this metabolism is called anaerobic (without oxygen) glycolysis (sugar destruction) and anaerobic respiration.

There: your dose of turtle trivia! Now I also appreciate why the University of Guelph in Ontario had an entire course dedicated to adaptive physiology of diving animals. Sharing neat facts are one thing, but imagine how complicated it is when you look at it in depth!

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