Kolkata: How far can Olive Ridley turtles migrate? Over 9,000 km, according to a recent publication on this threatened species of marine turtles known for its en masse congregation for laying eggs on selected beaches.
Using satellite telemetry, scientists from Odisha Biodiversity Board, Zoological Survey of India and Wildlife Institute of India have tracked the movement of Olive Ridley turtles from Odisha in the east to Sri Lanka in the south, beyond in the northern Indian Ocean, and back to the Bay of Bengal.
“With a maximum travel distance of 9,626 km, and two additional tracks measuring 9,417 and 8,579 km, we believe this study documents the longest satellite tracks ever recorded for Olive Ridleys,” states the publication, titled Movements of Olive Ridley Turtles in the Bay of Bengal, India, Determined via Satellite Telemetry .
The paper was published this month in the Chelonian Conservation and Biology , a peer-reviewed semi-annual scientific international journal of turtle and tortoise research.
Basudev Tripathy, member of IUCN-Marine Turtle Specialist Group and one of the authors of the publication, said that while migration of Olive Ridleys post their nesting from Odisha is known among the scientific community, that they can travel such long distances is really an important finding.
“Mapping the movement of Olive Ridley turtles recorded through satellite telemetry shows that they moved from their breeding grounds along the coasts in Odisha towards Sri Lanka between mid-April and late May; and around July they made a U-like curve, returning to Bay of Bengal,” Dr. Tripathy told The Hindu .
Earlier attempts to track their movement, in 2004, could not reveal much since the transmitters lasted only for a few months. In 2009, 14 turtles — three males and 11 females — were fixed with transmitters at Gahirmatha in Odisha. The tracking duration of these turtles varied from a minimum 7 days to the highest of 331 days.
The longest migration, of 9,626 km, was recorded in a female turtle tracked for 279 days. Two other female turtles also recorded high migration: the one tracked for the longest, 331 days, travelled 9,417 km; and the one tracked for 239 days travelled 8,759 km. Of the 14 tracked turtles, 10 travelled more than 5,000 km.
The females and males showed mean speeds of 2.65 and 1.91 km/hr respectively.
“This appears substantially faster than Olive Ridley turtle movements in other parts of the world. In northern Australia, Olive Ridleys have been shown to move at 0.87 to 1.54 km/hr,” said Satyaranjan Behara, another author of the publication.
Sea turtles spend majority of their life in the coastal and deeper waters of the ocean.
“Though the study tracks the migration of Olive Ridley turtles, we could not throw much light on their foraging behaviour — what do these species feed on and how deep in the ocean they forage. More studies are required to be undertaken to know about these species,” Dr. Tripathy said.
