biology zoology blog turtles animals diving

And the Gold Medal in Diving Goes to ……the Turtle!

The Turtle is a Gold medal diver

With a bit of exercise and healthy lungs, anybody can do what I could do even a few years ago: holding my breath and staying underwater for 2-3 minutes. The lazy South American sloth isn’t a good diver, but should the branch it clings on break off and the animal finds itself under-water, it can indeed hold its breath for 10-15 minutes; it’s simply quite a tough animal. But there is, of course, a limit to the duration anyone can stop breathing and ducks, for instance, can do much better than the average human. They, and other diving vertebrates as well, slow down their heart beats during the under-water period, which allows them to remain without oxygen longer in the submersed condition than in air with a normal heart beat. But while a duck’s dive would rarely exceed 10 minutes, that of the emperor penguin can last for 20 minutes and may take the bird to depths of around 200 m.

Still longer dives have been recorded in seals, whales and the alligator. Long as well as deep diving animals tend to have generally a greater volume of blood in their bodies than non-diving species. This allows the divers not only to increase oxygen levels in their blood, but also to transport and supply oxygen to organs that need it more efficiently. Diving specialists also exhale prior to a dive to avoid the “bends”, a condition brought about by the different pressures and gas solubilities on deep dives. Two hour dives and depths of 2,000 metres or even more have reliably been recorded for the master amongst the diving mammals, the sperm whale. It visits such incredible depths in search of its food, which includes the giant squid. However, the all-time-record of staying under water without surfacing for animals equipped with lungs to breathe in air? Who holds that record and what is the longest time the record holder can stay under water?

Well, that record is held by North American swamp turtles, some of which spend more than half a year under water (and ice) before re-surfacing. Their incredible ability to remain submerged for such a long period is due to a combination of several factors of which the low water temperature in winter, the proverbial slowness of these reptiles and an ability of the submersed turtle to take up some oxygen from the water and to expel CO2 by extra-pulmonary means, are the most obvious ones. Extra-pulmonary means that the lungs are not involved in the gas exchange and that the latter takes place across the thin skin layer of then inside of the mouth of the turtle. A somewhat similar gas exchange method is used by diving sea-snakes, but in their case it’s the gums that are involved. A vertebrate that never has to surface and breathe at all (being on a permanent dive so-to-speak) is the Lake Titica frog: it breathes through its loose and flappy skin that covers its entire body, but it doesn’t count as a “diver”. Therefore, we must return to the swamp turtles.

On their record-making long dives the turtles do not move around much and sit more or less motionlessly half-buried in the mud of the ice-covered pond or lake until the water warms up in spring. Food does not interest them during their record long winter dives and mating instincts are on halt, which teaches us that whether human or animal, for records you’ve got to be prepared to make certain sacrifices.

© Dr V.B. Meyer-Rochow and, 2018.
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