Bhubaneswar: With the Olive Ridley turtles facing risk due to global warming and climate change, coastal erosion leading to shifting of shoreline has severely impacted their mass nesting that commenced after a delay of over a month at Odisha’s Gahirmatha marine sanctuary, considered world's largest rookery of the marine species.
A recent global study on ‘Dynamic shoreline alterations and their impacts on Olive Ridley turtle nesting site in Gahirmatha’, has flagged concerns over significant erosion in shoreline that shifted around 14-km northward of the nesting site.
The Odisha coastline, stretching over 480 km, hosts mass nesting activities predominantly at three rookeries - Gahirmatha marine wildlife sanctuary, Devi river mouth, and Rushikulya river mouth.
The Gahirmatha sanctuary covers a total area of 27 sq km and extends approximately 35 km along the coastline, from the Brahmani river mouth in the south to the Dhamra river mouth in the north. It serves as an essential habitat for a wide range of flora and fauna, playing a critical role in regional biodiversity.
The study by researchers from three Indian universities and two from Brazil who focused on the coastal stretch extending from Mahanadi river mouth in the south to Dhamra Port in the north observed most significant erosion in the stretch from Barunei river mouth to Maipura river mouth while the highest accretion was recorded in the area stretching from Hukitola to Barunei river mouth.
In Gahirmatha, turtle mass nesting sites have gradually shifted from mainland beaches to island areas due to heavy erosion. Distinct shoreline changes observed along the Gahirmatha coast included the change near Mahanadi river mouth, gradual deposition of Hukitola spit moving northward, Ekakula spit near Maipura river mouth, and Wheeler group of islands.
In the early 1970s, mass nesting primarily occurred along Satabhaya to Ekakula beach. Gahirmatha came to the spotlight from 1974 onwards after the turtles started mass nesting on a 10 km stretch of mainland beach near Bhitarkanika extending up to Ekakula beach. By the early 1980s, mass nesting was observed near Ekakula Nasi beach.
“Coastal flooding and erosion resulted in a reduction of beach width, prompting sea turtles to shift their mass nesting activities to the emergent sandbar. The flooding of Maipura river estuary, which empties into the Bay of Bengal to the east, disrupted the continuity of the mainland beach. This led to the separation of the mass nesting beaches,” said professor of Geography department at FM University Manoranjan Mishra.
The super cyclone of late 1999, which made landfall along the Odisha coast, resulted in extensive erosion of coastal beaches and landforms. Coupled with enhanced river discharge, this led to increased sediment deposition along the spit and barrier bar, extending the Ekakula spit by over two km from 1990 to 2012.
Decadal change analysis of a 95-km stretch revealed a correlation between mass nesting and erosion and accretion rates in certain years. In 2020–2021, around 90% of transects experienced erosion, coinciding with a roughly 50% decline in mass nesting during 2021.
Similarly, during 2015–2016, erosion affected about 78% of transects, and there was a significant decrease in the number of mass-nesting turtles in 2016 compared to the previous year. High erosion rates were observed from Brahmani river mouth to Maipura mouth during 1995–1996, followed by a decrease in mass nesting numbers in 1997 and 1998, dropping from 2.9 lakh to 50,000. The researchers attributed the decline to habitat loss, specifically the reduction in beach length suitable for nesting.
“Increase in the accretion rate in some areas also positively influenced mass nesting. For instance, in 1994 and 1995, the number of mass-nesting turtles remained relatively stable as the accretion rate exceeded erosion. The absence of mass nesting in 2014, followed by a significant occurrence of 40,000 nests in 2015, can be attributed to increased accretion. The number of mass-nesting sea turtles increased in 2021–2022 as accretion was more prevalent than erosion,” Prof Mishra said.
The study findings suggested that the mass nesting of sea turtles tends to decrease when erosion at mass nesting sites creates conditions unfavourable for nesting, egg laying and successful hatchling emergence. Therefore, the dynamics of erosion and accretion play a crucial role in determining suitable environments for turtle nesting, said associate professor of marine sciences at Berhampur University Tamoghna Acharyya.
The study underscored the necessity for proactive measures, encompassing enforcement of current protective regulations and development of novel strategies to mitigate the effects of human activities and natural habitat changes. Such measures are imperative not only for the preservation of turtles but also for sustaining the overall health of marine ecosystems, added Prof Mishra.
