A record-breaking mass nesting by 3.8 lakh endangered olive ridley turtles ( Lepidochelys olivacea ) took place at the Rushikulya rookery coast in Ganjam district of Odisha in February 2017. Interestingly, no mass nesting had taken place at the site a year ago.
It was then suspected that several environmental factors, including chemical factors like salinity of the beach and the sea near the coast, may have prompted these marine reptiles to give the coast a miss in 2016.
Mass nesting
According to experts, most mass nesting sites of olive ridley turtles in the world are located near river mouths, where salinity is low. However, a lot still needs to be explored with regard to the influence of the salinity factor as not much is known about the relation between mass nesting by these endangered turtles and coastline salinity.
This behaviour, however, has prompted experts to study turtle sensing superpowers.
Explaining what may have prompted the mass nesting, Berhampur Divisional Forest Officer (DFO) Ashis Kumar Behera said a sandbar emerged at the mouth of Rushikulya river near Purunabandha this year. This, he added, prevented fresh water from the river from entering the sea directly.
“So the fresh water started flowing northward. This must’ve decreased the salinity of sea water near the coast towards north of the river mouth,” said Mr. Behera. Usually, the DFO added, mass nesting takes place between Gokharkuda and new Podampeta, where the effect of fresh river water diverted by the sandbar may be high.
Low salinity also means more small fish and insects, which are food for the turtles near the coast during mating and mass nesting seasons. The corrosive effect of salinity on eggshells cannot be ignored either.
“Olive ridley turtles bury their eggs on the beach. These eggs incubate with the help of sand heat for 45 to 50 days. High sand salinity may damage eggshells, while low salinity will minimise the corrosive effect,” said Mr. Behera.
It’s possible the olive ridleys took the salinity factor into account while nesting at Rushikulya rookery coast this year, but what remains unanswered is how they sensed it.
Many questions
According to Bivash Pandav, a scientist with the Wildlife Institute of India (WII), several mysteries related to the life, migration and mass nesting of olive ridleys are yet to be unravelled.
Dr. Pandav, who has been studying olive ridleys since decades, said a proper study of sea salinity levels near the coast in relation to the extent of mass nesting during past years will have to be taken up to understand the relation between salinity and nesting behaviour.
