Unravelling a turtle mystery

30 September 2007


For decades, there has been a wonderful mystery that has baffled marine biologists.  The question is, where do baby turtles go?

Sea turtles, as their name suggests, live their lives at sea, with females returning to land to lay their eggs on beaches.  And after the tiny baby turtles have hatched, they crawl down the beach, fight their way through the pounding surf and make their way back out to sea where they completely disappear into the wide blue ocean.

Until now we've had absolutely no idea where young turtles go or what they do until they turn up five years later closer to shore and much, much bigger.

Now at least part of that puzzle has been solved, thanks to a team of scientists from the Archie Carr Center for Sea Turtle Research in Florida who have been studying Green turtles from the Bahamas in the Caribbean.  

The researchers took small samples of the hard shells from Green turtles and analysed them for the presence of particular isotopes of carbon and nitrogen - most elements have several different isotopes that occur naturally with each isotope having a different number of neutrons, giving each them a slightly different atomic mass.

Different types of plants and animals naturally take up different amounts of the various isotopes in the environment, for example of the three main carbon isotopes, carbon 12, 13 and 14.  And by measuring the ratio of different carbon and nitrogen isotopes in sea turtle shells, the team found out what types of food the turtles feed on.

These isotope studies have shed a much-needed beam of light into the mysterious world of Green turtles, and shown that these creatures that we normally think of as vegetarian - feeding on seagrasses and seaweeds - are in fact carnivores when they swim out to sea where they adopt a diet of jellyfish and other marine animals.

This latest study also indicates that the green turtles stay far out at sea for the first three to five years of their life, before swimming back into shallower coastal waters.

The really neat thing about this type of study is that it can by applied to all sorts of other animals, by sampling feathers, skins, fish scales and bones, allowing us to learn more about what animals get up to when we can't see them.

In fact this is the same sort of technique that we talked about a few weeks ago, with a study that showed how penguins in the Antarctic have shifted their diets from mostly eating fish to taking advantage of the large populations of krill in the Southern Ocean.


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