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Thursday, July 9, 2009

Turtles of Sri Lanka

Turtles are reptiles, which, together With tortoises and Terrapins, are included in the order Chelonia (or Testudines). This order Comprises about 210 species; including the seven marine turtles. The ‘Chelonians’ were probably well established about 200 to 185 million years ago and had acquired the present day form and aquatic characteristics by some 90 million years back.

They are thus the most ancient living reptiles, Their Predecessors having co-existed with dinosaurs. These predecessors included Archelon, a marine turtle with a 3.36 meter Carapace and a close resemblance to species of today. P.E.P. Deraniyagala described in 1937 a Fossil of a Sri Lankan marine turtle of the Miocene (geological) era which belonged to a species he later named as Miocaretta lankae.

The seven species of marine turtle which remain in existence to day are

1- Loggerhead (Caretta caretta, Linnaeus, 1785)

2- Flatback (Chelonia depressa, garman, 1880)

3- Green turtle.Two forms (Chelonia mydas mydas, Linnaeus,1758 and Chelonia mydas agassizi,Boncourt,1868)

4- Hawksbill. Two forms (Eretimochelys imbricata, Linnaeus, 1766 and Eretmochelys imbricata bissa

5- Kemp's (Or Atlantic) Ridley (Lepidochelys kempi, Garman 1880)

6- Olive (Or Pacific) Ridley or olive loggerhead (Lepidochelys olivacea, Eschscholtz, 1829),
Commonest sea turtle in Sri lankan waters

7- Leathery turtle Leatherback, trunkback or Luthe (Dermochelys coriacea, Linnaeus, 1766)

This species is placed in a different family from the other marine turtle. This species and the kemp's Ridley are probably the closest of the marine turtle ton extinction.

Some experts recognize Chelonia agassizi as a species in its own right and not as a subspecies. The Flatback is also called natator depressus. Other then the kemp's Ridley, each of the above of the species nest in at least one of the countries bordering the Indian Ocean. Of these six species, five nest in Sri Lanka. The sixth, the Flatback, may (infrequently) be carried here by unusual hydrographic conditions after breeding in tropical Australia.

The breeding habits of marine turtles are one of their most interesting features. Mating takes place in the sea and the females may approach land singly or in numbers in an arribada. For instance, in an arribada of Kemp's Ridley turtles in Mexico in 1947 over 40’000 individuals were recorded emerging to nest on one mile of beach in one day. Large arribadas of olive Ridleys have been reported from Orissa. A minor arribada of around one hundred olive Ridleys was observed in Sri Lanka be fore the cyclone of December 1978.Stormy weather may help the survival of eggs by smoothing over the disturbance to the beach sand caused by turtle tracks and nest making. Concealment is further aided by nesting taking place at high tide at night in the case of the Indian Ocean turtle. (The kemp's Ridley of the Atlantic Ocean lays its eggs in the daytime possibly as a protection against a nocturnal coyote). High tide conditions are preferred in order to assist the ponderous female further up the beach and the prevent the nest of eggs getting inundated during incubation.

The overage time required for incubation varies according to the species of turtle as does the number of eggs per nest and the frequency of nesting per year clutch of eggs of Hawksbill turtle may overage 50. Different species may nest every year (e.g. Green turtles). Several clutches may be laid in a season or nesting year. The temperature at the center of small or large clutches of eggs is higher then the edges due to the heat generated due to metabolism.

The temperature at which incubation of turtle eggs takes place has two effects, which are not observed on incubation of birds eggs. One is that the incubation period may be significantly shorter at higher temperatures. Thus when green turtle eggs are incubated at 32c 48 days may be required before hatching Commences; as against around 55 days at 30c or some 80 days at 27c.

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