Assessing the Human Impact on Olive Ridley Sea Turtles
The olive ridley sea turtle, also known commonly as the Pacific ridley sea turtle, are the most abundant of all sea turtles found in the world yet some argue they are also the most exploited. Despite their abundant population, the ridley turtles are internationally listed as “vulnerable” (facing a high risk of extinction in the near future) by the International Union for Conservation of Natural Resources (IUCN) due to their rapidly declining population as a result from centuries of over-exploitation. According to the last report population round-up in 2008 the olive ridley have lost over 50% of its population from the historical population of 10 million to now 800,000.
Olive Ridley Habitat
The olive ridley, named on the color of its shell—an olive green hue — is mainly a plegic sea turtle and is among the smallest of the world’s sea turtles. It is closely related to the Kemp’s ridley with primary difference that olive ridley are found only in the warmer waters of the Pacific, Indian, and Atlantic Oceans. They have an annual migration from pelagic foraging, to coastal breeding and nesting grounds, and back to pelagic foraging.
Olive Ridley distribution map: Red circles are major nesting grounds; Yellow circles are minor nesting beaches.
What are they known for? their unique synchronised mass nesting called arribada (spanish for arrival)! It is recognised as one of the most extraordinary nesting habits in the natural world. Thousands of females return to the same beach from where they hatched, to lay their eggs. Solitary nesting occurs extensively throughout this species’ range, and nesting has been documented in approximately 40 countries worldwide. Arribada nesting, however, occurs on only a few beaches worldwide. An average clutch size is over 100 eggs, which require a 52 to 58 day incubation period.
Female turtles lay their eggs in conical nests just about 1.5 feet deep, which they laboriously dig with their hind flippers. The hatchlings emerge from the eggs after 45-60 days and crawl into the sea in the absence of their parents.
Olive Ridley In India
In the Indian Ocean, its greatest abundance is in eastern India and Sri Lanka. The coast of Odisha in India is one the largest mass nesting sites for the olive ridley. Gahirmatha beach in Kendrapara district is acclaimed as the world’s largest-known nesting ground of these endangered marine species. Apart from Gahirmatha, these aquatic animals turn up at Rushikulya river mouth and Devi river mouth, also Odisha coast, for mass nesting.
In 1991, over 600,000 turtles nested along the coast of Odisha in one week. Around 730,000 olive ridley turtles turned up for their annual sojourn of mass nesting in the 2019-20 season at Odisha coast. In a recent citing in 2020, the Agonda beach in Goa witnessed its first ever olive ridley turtle nest. While the nesting period usually starts in September, it appears that it has now shifted to December – January and ending in March – April. It is believed this shift is due to climate change.
All stages of a sea turtle’s life are affected by environmental conditions such as temperature—even the sex of offspring.
Mass Nesting Beaches at Odisha coast
Incase of olive ridley, the warmer the nest beach conditions, the more female hatchlings that emerge from the eggs. Unusually warm temperatures caused by climate change could be disrupting normal sex ratios, resulting in fewer male baby turtles. The reason for this phenomenon is unknown.
Although olive ridleys are famed for their arribadas, many of the nesting grounds can only support relatively small to moderate-sized aggregations (about 1,000 nesting females). Their vulnerable status comes from the fact that these turtles nest in a very small number of places, and consequently any disturbance, such as an increase in light pollution, to even one nest beach can have huge repercussions on the entire population.
For example, sea turtles nest on sandy tropical beaches and when the hatchlings emerge, they head towards the brightest and lowest horizon. On undeveloped beaches this is usually the waterline; however, on developed beaches, artificial lights can cause hatchlings to crawl towards the source of light or in random directions making them more vulnerable to prey attacks. Adult sea turtles exhibit similar disorientation in the presence of light and they have also been documented to avoid illuminated areas when selecting nesting habitat.
Noted to be largely a diverse species in terms of habitat, ridley turtles have been finding new nesting grounds due to decades of human exploitation and urban development at these nesting beaches.
What is the key reason for declining ridley turtle population ?
The following are the key threats from human developmental activities:
- Unsustainable harvest of eggs
- Fisheries Bycatch
- Habitat Degradation
- Vessel Strikes
Olive-ridleys face serious threats across their migratory route, habitat, and nesting beaches due to human activities such as turtle unfriendly fishing practices and, development and exploitation of nesting beaches for ports and tourist centres. Between 1993 and 2003, more than 100,000 olive ridley turtles were reported dead in Odisha, India, from fishery-related practices.
Once slaughtered in their hundreds of thousands for meat and leather, olive ridleys have yet to recover from decades of over-exploitation. Though international trade in these turtles and their products is banned under CITES Appendix I, they are still extensively poached for their meat, shell, and leather, and their eggs, though illegal to harvest, have a significantly large market around the coastal regions. Illegal egg poaching, turtle harvesting and nest destruction by humans is so rampant that only 1 to 8 percent of eggs laid during arribadas hatch.
The Olive ridley eggs and hatchlings are the chief wildlife prey. Notably, the jaguar is the only cat with a strong enough bite to penetrate a sea turtle’s shell, thought to be an evolutionary adaptation from the current anthropocene extinction event. The female turtles are defenseless against a strong predator like jaguar, which have been observed to prey more on these turtles possibly due to the loss of their own habitat.
Nonetheless, the human over-exploitation of the olive ridley eggs and the deaths in bycatch remain the key threat driving the species rapidly declining population. While the species has a wide range, the number of important breeding sites is very restricted, so efforts to protect their major beaches are vital. It is estimated that approximately 1 hatchling survives to reach adulthood for every 1000 hatchlings that enter the sea waters.
‘Saving turtles is good for tourism and the local economy’
Sea turtles play a key role in maintaining a healthy coral reef and the balance of the marine food chain. Ever since the imminent threat to species’ extinction, several local and global initiatives and projects have been implemented to protect and conserve the olive ridley sea turtles.
In western coast Mexico’s nesting grounds, through engagement of the villagers, who initially illegally poached the eggs, a regulated and legal collection of turtle eggs was engable that not only helped the villagers continue to earn their livelihoods but also played a crucial role in protecting the remaining eggs and the hatchlings from predators.
In India’s Odisha coast, WWF along with fishermen community, has been involved in protecting the Olive ridley rookery at the mass nesting site at Rushikulaya, in Orissa, by fencing off the nesting area and patrolling it till hatching and ensuring a safe passage for the hatchlings to the sea. To reduce accidental killing in India, the Orissa government has made it mandatory for trawls to use Turtle Excluder Devices (TEDs), a net specially designed with an exit cover which allows the turtles to escape while retaining the catch.
The Odish government enforced a fishing ban from Nov 2019 – May 2020 to protect the olive ridley mass nesting. Around 8000 fishermen were promised compensation against the ban. In addition, a proposal has been made to establish a permanent research centre near the Rushikulya rookery on the Odisha coast to study the mass nesting of Olive Ridleys and the environmental factors related to it.
In Maharashtra, through a Marine Turtle Conservation Program initiated by NGO Sahyadri Nisarga Mitra (SNM) in 2010. The first year, 50 nests were protected on the beaches of Velas. The conservation program has since spread across the entire Maharashtra coastline.
Since 2010, around 150 nests have been protected, with 8,290 hatchlings successfully released. Even villagers who once relied on eggs for income recognize the importance of protecting the Olive Ridley nests.
Today, an annual Velas Turtle Festival attracts thousands of tourists from across the country, and villagers enjoy the extra income derived from providing homestays for tourists. Some villagers earn as much as 100,000 rupees (more than US$1,400), and many contribute 10% of their festival income to the Marine Turtle Conservation Fund.
- 8,290 hatchlings successfully released to their natural environment
- 7 coastal villages have launched the Marine Turtle Conservation Program
- Over 1,600 eggs successfully translocated to the hatchery since 2010
The Olive Ridley are known to be highly polygamous and polyandrous with a high degree of genetic variation that helps them to be more adaptable to the changing environment. With a growing human population, need for food and urban development is inevitable, including large dependency on marine industry. Through collaboration with local NGOs the awareness of sustainable practices and economic benefits of olive ridleys are being better understood by the locals who once exploited the species. With proactive conservation efforts and sustainable development methods, particularly at the mass nesting beaches, there is still scope to improve the population of olive ridleys and change their ‘Vulnerable’ (V) status to ‘Not Vulnerable’ (NT) in IUCN list, and not let it decline to internationally “Endangered” (En) red list.