Green turtle diet unravalled

 
By Kirtiman Awasthi
Published: Wednesday 31 October 2007

No more vegetarian: The turtle where do green sea turtles disappear soon after they are born? This question has been cause for scientific curiosity for long. New study from the us suggests the turtles spend their early period in the open ocean, feeding on jellyfish. The turtles (Chelonia mydas) had been thought to be vegetarians.

The results help solve a 50-year-old mystery about the hideouts of the turtles which are classified as endangered species in the iucn Red List. Green turtles are found on beaches worldwide including India; but are endangered as they were heavily consumed for food and now threatened due to coastal habitat degradation and marine pollution.

Conservation point The 'lost years' was first discussed in 1952 by biologist Archie Carr in his book The Handbook of Turtle. Now researchers from the Archie Carr Center for Sea Turtle Research at the University of Florida in the us have found that the turtles move closer to the shore after spending time in the open sea and switch to a vegetarian diet on sea grass. This period has already been well observed and studied by scientists.

The researchers reached the conclusions by analysing isotopes of carbon and nitrogen in turtle shells. The analysis revealed the ratio of nitrogen isotopes in the older and new shell. It was found to be 'significantly different'. The fact that this difference was much similar to the observations made on sea turtles which are carnivorous has helped the researchers conclude that the turtles spend their first three to five years in the open ocean feeding on marine organisms. The findings have been published online in the journal Biology Letters on September 18, 2007.

Stable isotopes of nitrogen and carbon are used to study migration, feeding habits and the status of a species in a food chain. The higher an animal on the food chain, the more it accumulates isotopes. Ratio between heavy to light isotopes can talk about the eating habits of the organism, whether it is herbivorous or carnivorous. While nitrogen isotopes are used in determining their position in the food chain, carbon isotopes can reveal habitats the animal uses.

Researchers analysed 44 turtles captured from Great Inagua in the Bahamas and studied the isotope records in their scute tissue--the hard tissue covering the bony shell. Scute is an immovable tissue which retains a history of the animal's diet and habitat.

The findings are important since conservation plans for green sea turtles have so far excluded this period owing to lack of sufficient data on their whereabouts. "You can't protect something, if you don't know where it is," said Karen Bjorndal, director of Archie Carr Center.

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