OLIVE RIDLEY TURTLES

Jayanthi Rengun

A turtle is a reptile with a bony or leathery shell. Any shelled reptile can be called a turtle, but in North America people commonly use the word tortoise to designate members of a family of turtles that live entirely on land, reserving the word turtle for species that live in or near water.

Classification
Kingdom:          Animalia
Phylum:            Chordata
Class:                Reptilia
Order:               Testudines
Family:             Cheloniidae
Genus:              Lepidochelys
Species:            Lepidochelys olivacea

 

Fig 1

Turtles are ancient life forms that first appeared on Earth during the Triassic Period, which extended from about 240 million to 205 million years ago. Turtles survived the disasters that wiped out the dinosaurs and many other creatures at the end of   the Mesozoic Era about 65 million years ago. The earliest known fossil turtles were similar to the turtles that live today. The earliest turtles had teeth, unlike today’s, which are toothless and use their sharp jaws to bite and handle food.

There are about 270 living species of turtles, which are grouped into 12 or 13 families. These families are further classified into two suborders: side-necked turtles and hidden-necked turtles. Side-necked turtles protect their heads by folding their necks sideways under the top edge of the shell. Hidden-necked turtles pull their heads directly into the shell, using an up- and-down motion of the neck. They are more widespread than side-necked turtles and include all the ocean and freshwater turtles of gets Asia.

The Olive Ridley Turtle was listed endangered on July 28, 1978 by IUCN and their current estimated population is unknown.

 Turtle and Indian literature

The feature of the turtle drawing its appendages into the shell of its body finds mention in the Tirukkural under the subtitle “Possession of self control”.

ஒருமையுள் ஆமைப்போல் ஐந்தடக்கல் ஆற்றின்

எழுமையும் ஏமாப் புடைத்து

Meaning: “If one could liken to a tortoise and draw in one’s own five senses, throughout one’s sevenfold births, one’s great strength will thence survive”.

The story goes that when the Gods and demons churned the milky ocean for ambrosia. Lord Vishnu took the form of a turtle on which was placed the Meru mountain, while Aadishesan was used as a rope to obtain the ambrosia. In all the references the importance of the shell of the turtle is highlighted.

Olive Ridley

The Olive Ridley (Lepidochelys olivacea) is the smallest of the sea turtles weighing about 140 pounds (65 kilos) and measuring about 2 feet (60 cm) along its carapace and named after the olive color of its heart- shaped shell. They inhabit the tropical and subtropical coastal bays and estuaries and are migratory, often travelling thousands of kilometres between feeding and nesting sites.

Geographical spread

This circumglobal species is present in the geographic ranges of the tropical and subtropical regions of the Pacific, Atlantic and Indian Oceans as well as the Southern Atlantic Ocean.

The Olive Ridley is omnivorous; the main food items recorded are crabs and shrimps, pelagic tunicates, sea grasses, jellyfish and also fish eggs. Olive Ridleys have been captured in prawn trawls at depths of 80 to 110 m. so they are certainly capable of foraging at relatively greater depth.

Females of Lepidochelys species tend to nest in large synchronised concentrations (arribadas-a Spanish word meaning ‘mass arrivals’), which may be an adaptation against predation, the predators being overwhelmed by sheer numbers resulting in one main reason for the survival and success of this species. Very large arribadas now occur in only two regions, at two beaches in Orissa State (northeast peninsular India), on the Bay of Bengal, and at two beaches in Costa Rica, on the east Pacific. The coast along Chennai is also a minor area where Olive Ridleys breed.

Nesting emergence mainly happens at night. The turtles come ashore at night during high tide and dig cavities about feet deep to lay eggs. Once the female has excavated a nest as deep as her hind flippers can reach, she begins to lay her eggs. After the eggs are laid they cover the nest with sand. A turtle usually nests thrice between December and April. A turtle lays about 100-180 eggs during the first visit, 60-80 eggs on the second and 30-60 on the third visit. After the eggs are laid, the turtles go back to the sea and never come back.

Fig 2

When the eggs hatch after 52-55 days, the two-inch long hatchlings scramble out of the deep pit, soon after high tide, at night. Hearing the sea, they begin to move towards the waves in great haste. Upon reaching adulthood, they return to the shore where they were born, for nesting.

Current threats

Turtles and their cousins, the tortoises, are among those animals that have been naturally blessed with a long life. Three major threats to Olive Ridley populations have been identified, viz., commercial harvest of adults, incidental catch in shrimp trawls, and harvest of eggs from nest beaches. These factors are of differing significance in different areas. Egg and hatchling predators include a very wide variety of birds and mammals, including hawks, vultures, caracaras, raccoons and coyotes. The Olive Ridley has been and will always be vulnerable, because such a large proportion of its reproductive effort is concentrated only in a few locations.

Human impact on Olive Ridley sea turtles

Pesticides, heavy metals and PCB’s have been detected in turtles and eggs, but the effect on them is unknown. Marine turtles are at risk when encountering an oil spill. Respiration, skin, blood chemistry and salt gland function are affected. Olive Ridley turtles eat a wide variety of marine debris such as plastic bags, plastic and styrofoam pieces, tar balls, balloons and raw plastic pellets. Effects of consumption include interference in metabolism or gut function, even at low levels of ingestion, as well as absorption of toxic by-products. In areas where recreational boating and ship traffic is intense, propeller and collision injuries are common.

Conservation efforts

There is a ban on all Olive Ridley products under the Convention on International Trade in Endangered Species of Wild Flora and Fauna (CITES).

Restricted fishing zones should be established in areas of high turtle concentration, particularly off major nesting beaches and high priority given to the development of fishing equipment which prevents incidental take of sea turtles.

Regional agreements on conservation are highly desirable, and ought to include large scale tagging programmes.

Olive Ridley hatchlings can be raised in captivity. Presently there are no known commercial mariculture projects for Olive Ridleys.

The leather trade should be brought to an end as soon as possible.

Existing laws should be enforced and additional National Parks and Reserves adequately created and protected.

The Orissa Marine Fishing (Regulation) Act, 1982 already bans any kind of mechanised fishing within five kilometres of the shoreline, which is precisely where Olive Ridleys congregate during the breeding season.

Source:

Eco News, Vol 9, No 4, January to March, 2004

 

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