By Stacey Venzel
Of the three Testudines categories, only terrapins and turtles swim; tortoises do not. Adaptations like flippers and underwater breathing help some species live more in the water than on land.
In general, if a Testudine has flipper-like feet, it can swim, but not all chelonians swim. How long they swim, too, is determined by a number of factors. However, there are pros and cons to being an aquatic dweller.
DO ALL TURTLES HAVE FLIPPERS?
Only a handful of aquatic turtles have flippers, but water-dwellers lacking flippers still do a decent job stroking through the water. All seven species of sea turtles have flippers and one freshwater species, the pig-nosed turtle, also has full-fledged flippers. The remaining swimmers rely on webbing.
Flat-footed, dome-shelled tortoises would have a hard time swimming through the water. Imagine you jump into the pool with overturned buckets tied to your feet and back. It would be difficult for you to swim a lap, just like it would be difficult to make it from one end of the pond to the other if you are an Aldabra tortoise. Adult gopher tortoises have even been documented drowning because their body shape is made for sinking, not floating or swimming.
The greater the amount of webbing between the toes of a turtle, the more time it spends in the water. Box turtles are typically more terrestrial than aquatic, but they do have slight webbing to
help them soak in muddy lakes or mate in the water on hot days. Many softshell species have full webbing in all four feet but still do not qualify as flippered individuals. The broad flippers and streamlined shells of sea turtles help them fight ocean currents and swim at bursts of speed up to 22 mph.
To increase body temperature, turtles occasionally bask on the water’s surface. Sea turtles can be seen doing this in the ocean not only to warm up but also to help save energy and avoid predators.
HOLDING THEIR BREATH
Like humans, most Testudines have lungs and breath oxygen from the air, forcing them to hold their breath when submerged. The longest a human has been documented holding his breath underwater was 24 minutes, according to the Guiness Book of World Records, but the green sea turtle can hold its breath underwater for five hours.
BREATHING THROUGH THEIR BUTTS
Water has oxygen just like air, but it is more difficult to obtain. All turtles rely on their lungs to breathe oxygen, but some species have developed means of breathing underwater to limit their trips to the surface. Most notable of them is the Fitzroy river turtle which has organs resembling gills in its cloaca. Like a fish, it can obtain oxygen from flowing water, which is why it is often found in rivers, where they can remain submerged for up to nine hours by breathing through their butt!
DRINKING WATER TO BREATHE
Some turtles have thin enough skin for oxygenated water to pass through their cells. Other aquatic turtles can gulp water through their mouths, transfer the oxygen into their bloodstream, and then exit the deoxygenated water through their nose. The mud river turtle has specialized cells around its tiny tongue for underwater breathing.
A few species developed means of breathing just below the surface of the water with an appendage called a proboscis. The nose of the softshell turtle, for instance, is long and tube-like, acting like a snorkel that sticks out just above the water so that the turtle can breathe. This allows the animal to stay hidden from both predators and prey.
BENEFITS OF NOT SWIMMING
Tortoises benefit from not living in the water because they do not have to worry about sharks or other aquatic predators, including humans with their fishing hooks and nets. They also do not get parasites like leeches or have to worry as much about manmade disasters such as oil spills.
PROBLEMS OF NOT SWIMMING
Without sharks as predators, turtles still have to worry about being hunted on land. Humans pose a danger with their cars, often hitting turtles crossing the road. Out of the water, a tortoise’s shell can also peel and crack from overexposure to the sun.
Hope Babowice, “Like humans, some ocean creatures need to breathe air,” Daily Herald, August 9, 2011, http://www.dailyherald.com/article/20110809/news/708099955/.
Stephen Divers, Doug Mader, Current Therapy in Reptile Medicine & Surgery, (St. Louis, Elsevier Saunders, 2014), 205, 298-299.
Karen Eckert, David Gulko, Sea Turtles: An Ecological Guide (Honolulu, Mutual Publishing, 2004), 14, 17, 48-49, 56, 88, 90-91, 96-99.
Carl J Franklin, Turtles: An Extraordinary Natural History 245 Million Years in the Making (St. Paul, Voyageur Press, 2007), 20-22.
Whit Gibbons, Judy Greene, Turtle: The Animal Answer Guide (Baltimore, The John Hopkins University Press, 2009), 21-23, 41, 49.
Matt Walker, “Turtle ‘super tongue’ lets reptile survive underwater,” BBC News, May 20, 2010, http://news.bbc.co.uk/earth/hi/earth_news/newsid_8693000/8693794.stm.
“Sea Turtles,” Shark Reef Aquarium, http://www.sharkreef.com/teachers/pdf/turtles.pdf.