PUNE: A Zoological Survey Of India (ZSI)-Pune study found the world-famous Olive Ridley turtle nesting ground at Gahirmatha Marine Wildlife Sanctuary in Odisha has shifted a staggering 14km northwards over the last three decades owing to severe coastal erosion caused by climate change and human activities.
The peer-reviewed study, published in leading scientific journal Marine Pollution Bulletin by Elsevier, has analysed shoreline changes from 1990 to 2022 using satellite imagery and the digital shoreline analysis system software.It covered 929 transects across four zones in the nesting habitat. Dr Basudev Tripathy, scientist, ZSI-Pune, described the findings as a matter of concern for the future of Olive Ridley Arribada (mass nesting that recently started at Gahirmatha).
Turtle nesting zone shift leads to fears of crowding, egg loss
Federal University of Pernambuco-Brazil and Federal University of Paraíba-Brazil were also involved among others in the study, which covered 929 transects across four zones in the nesting habitat.
“The marine sanctuary hosts one of world’s largest congregations of these endangered marine reptiles. During the annual Arribada, millions of Olive Ridleys converge on Gahirmatha’s sandy beaches to lay eggs. However, rampant erosion has drastically reshaped the coastline, forcing the turtles to shift their nesting ground northwards by 14km, from the mainland to an adjacent island, after which there is no space,” Tripathy said.
According to Tripathy, the turtles are forced to lay eggs in a limited space as their number is far more than the area available. “This can lead to overcrowding and substantial egg loss. For instance, if 10,000 turtles lay eggs one night and depart, and then another 1,000 turtles arrive to lay eggs, the newcomers may be forced to dig up the previously established nests because of lack of space. Consequently, the eggs in those disturbed nests are likely to be crushed or exposed, rendering them nonviable,” Tripathy explained.
For shoreline change analysis, the study focused on the coastal stretch from the Mahanadi river mouth in the south to Dhamra port in the north. This coastline was divided into four zones based on natural landmarks, such as river mouths and sea beaches, as well as anthropogenic features like ports.
“Zone I was from Mahanadi river mouth to Hukitola bay and Zone II was from Hukitola bay to Brahmani river mouth. Zone III (identified as the most vulnerable segment) included erosion-prone Pentha and Satabhaya Sea beaches. Despite mitigation efforts, erosion remains a critical concern in this zone. Historically, Olive Ridley turtle mass nesting occurred here. But severe erosion has caused the nesting site to shift further north. Zone IV, from Maipura river mouth to Dhamra port, is the current location for the Olive Ridley turtle mass nesting, particularly around Wheeler Island,” Tripathy said.
The analysis revealed that Zone III, from Barunei river mouth to Maipura river mouth, experienced the most significant erosion, with 89.2% of the transects showing such trends. The mean shoreline change rate for the entire study period (1990-2022) was half a centimetre per year.
In 2020-2021, approximately 90% of transects experienced erosion, coinciding with a roughly 50% decline in mass nesting in 2021, Tripathy said. “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 year before. This decline was possibly linked to habitat loss, specifically the reduction in beach length suitable for nesting.” Tripathy said.
Odisha coast, particularly in Gahirmatha marine wildlife sanctuary region, has experienced significant erosion because of both natural and human-induced factors, the study revealed. The natural causes include severe floods, frequent cyclonic events and storm surges, as well as heavy monsoonal rainfall, the study stated.
Manmade factors exacerbating erosion include coastal modifications that gradually increased erosion in Zone III. “While Gahirmatha marine wildlife sanctuary is protected, nearby developmental activities can indirectly impact it. Coastal interventions like installing erosion control structures in nearby beaches/ports divert wave action, intensifying erosion within the sanctuary’s beaches and threatening turtle nesting habitats. A holistic approach, considering ripple effects on adjacent ecosystems, is crucial,” said Tripathy.
The peer-reviewed study, published in leading scientific journal Marine Pollution Bulletin by Elsevier, has analysed shoreline changes from 1990 to 2022 using satellite imagery and the digital shoreline analysis system software.It covered 929 transects across four zones in the nesting habitat. Dr Basudev Tripathy, scientist, ZSI-Pune, described the findings as a matter of concern for the future of Olive Ridley Arribada (mass nesting that recently started at Gahirmatha).
Turtle nesting zone shift leads to fears of crowding, egg loss
Federal University of Pernambuco-Brazil and Federal University of Paraíba-Brazil were also involved among others in the study, which covered 929 transects across four zones in the nesting habitat.
“The marine sanctuary hosts one of world’s largest congregations of these endangered marine reptiles. During the annual Arribada, millions of Olive Ridleys converge on Gahirmatha’s sandy beaches to lay eggs. However, rampant erosion has drastically reshaped the coastline, forcing the turtles to shift their nesting ground northwards by 14km, from the mainland to an adjacent island, after which there is no space,” Tripathy said.
According to Tripathy, the turtles are forced to lay eggs in a limited space as their number is far more than the area available. “This can lead to overcrowding and substantial egg loss. For instance, if 10,000 turtles lay eggs one night and depart, and then another 1,000 turtles arrive to lay eggs, the newcomers may be forced to dig up the previously established nests because of lack of space. Consequently, the eggs in those disturbed nests are likely to be crushed or exposed, rendering them nonviable,” Tripathy explained.
For shoreline change analysis, the study focused on the coastal stretch from the Mahanadi river mouth in the south to Dhamra port in the north. This coastline was divided into four zones based on natural landmarks, such as river mouths and sea beaches, as well as anthropogenic features like ports.
“Zone I was from Mahanadi river mouth to Hukitola bay and Zone II was from Hukitola bay to Brahmani river mouth. Zone III (identified as the most vulnerable segment) included erosion-prone Pentha and Satabhaya Sea beaches. Despite mitigation efforts, erosion remains a critical concern in this zone. Historically, Olive Ridley turtle mass nesting occurred here. But severe erosion has caused the nesting site to shift further north. Zone IV, from Maipura river mouth to Dhamra port, is the current location for the Olive Ridley turtle mass nesting, particularly around Wheeler Island,” Tripathy said.
The analysis revealed that Zone III, from Barunei river mouth to Maipura river mouth, experienced the most significant erosion, with 89.2% of the transects showing such trends. The mean shoreline change rate for the entire study period (1990-2022) was half a centimetre per year.
In 2020-2021, approximately 90% of transects experienced erosion, coinciding with a roughly 50% decline in mass nesting in 2021, Tripathy said. “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 year before. This decline was possibly linked to habitat loss, specifically the reduction in beach length suitable for nesting.” Tripathy said.
Odisha coast, particularly in Gahirmatha marine wildlife sanctuary region, has experienced significant erosion because of both natural and human-induced factors, the study revealed. The natural causes include severe floods, frequent cyclonic events and storm surges, as well as heavy monsoonal rainfall, the study stated.
Manmade factors exacerbating erosion include coastal modifications that gradually increased erosion in Zone III. “While Gahirmatha marine wildlife sanctuary is protected, nearby developmental activities can indirectly impact it. Coastal interventions like installing erosion control structures in nearby beaches/ports divert wave action, intensifying erosion within the sanctuary’s beaches and threatening turtle nesting habitats. A holistic approach, considering ripple effects on adjacent ecosystems, is crucial,” said Tripathy.