Sea Turtle Hatchlings

They pack a big lunch

Green sea turtle Chelonia mydas
Green sea turtle
(Chelonia mydas)

sea turtle hatchlings
Green sea turtle hatchling

Photo: Manuel Heinrich Emha
Heron Island Research Station
Heron Island Research Station
(click to enlarge) Image: Nickj

Many sea turtle hatchlings don't survive their birthday — Or should I say hatchday? If they escape pouncing predators to reach the sea, these miniscule mariners must then evade swarming shoreside schools of famished fish in their bid for freedom. For turtles hatching on the Great Barrier Reef's coral cays the risks are high: as many as 30 percent meet their doom en route to the relative safety of deep waters.

But how much does their precarious passage cost these heroic hatchlings? David Booth from the University of Queensland decided to compute hatchling turtles' oxygen consumption rates during their swim for safety.

At the university's research station on Heron Island, Booth's laboratory is within meters of a green turtle nesting beach. Waiting as mothers-to-be lumbered ashore, Booth collected eggs as they were laid and moved them to the edge of the nesting site to protect them from the crushing bodies of other egg-laying mothers.

Several months later, when the eggs were hatching, Booth came back and intercepted hatchlings on their way to the sea. Back at the station, he fitted them with stylish lycra swimsuits and then attached them to force transducers. Next he placed them in a seawater aquarium.

As soon as they hit the water, the tiny turtles were swimming frenetically, tugging the cords attached to their force transducers. For 18 hours Booth measured their oxygen consumption as they swam.

At first they swam relentlessly. But as time went on, they gradually slowed, until after about 12 hours they took an occasional break.

The transducers measured precisely how hard the hatchlings swam. At first they were tugging with all their might and main, generating a force of 45 millinewtons. But this soon dropped to 35 millinewtons, and, eventually leveled off at 20 after about 12 hours. Oxygen consumption followed the same temporal pattern.

So what are the implications for the typical young turtle? Booth calculates that his subjects consumed a mean 4.79 kilojoules during their 18-hour swim. This implies, given the amount of energy contained in the average yolk sac, that sea turtle hatchlings can expect to survive about two weeks even without a meal.

No need to put another sandwich in the lunch-box!

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