Introduction

Sea turtles are among the most ancient and ecologically significant marine vertebrates, having evolved over 110 million years ago during the early Cretaceous period1,2,3. They survived global extinction events, such as the Cretaceous–Paleogene boundary and the Palaeocene–Eocene Thermal Maximum4,5. Sea turtles possess extraordinary evolutionary adaptations, including a streamlined carapace, muscular paddle-shaped flippers, and reproductive behaviours such as natal homing and false nesting2,6,7.

Sea turtles have a life cycle that spans both land and ocean, involving long migrations from feeding grounds to breeding and nesting sites, often covering thousands of kilometres and sometimes crossing entire ocean basins3. For example, Caretta caretta migrates from feeding areas off the coast of Japan to nesting beaches near California8. Nesting occurs mostly during the night on undisturbed to minimally disturbed beaches2,9,10,11,12,13,14,15,16. The female crawls on the beach and finds an ideal location to nest. Using her hind flippers, she digs an egg chamber about 50–75 cm deep2,17. Each female deposits a clutch of roughly 100–130 eggs and typically nests two or three times in the same season, with intervals of about 20–28 days between nesting events1,2,8,13,18,19,20.

Sea turtles are found throughout the world’s oceans, excluding the cold waters of the polar regions, and are keystone species across marine ecosystems2,3,21. A total of seven species of sea turtles exist worldwide2,3,22,23, with five species—Lepidochelys olivacea (Olive Ridley Sea Turtle), Chelonia mydas (Green Sea Turtle), Eretmochelys imbricata (Hawksbill Sea Turtle), Caretta caretta (Loggerhead Sea Turtle), and Dermochelys coriacea (Leatherback Sea Turtle)—found in Indian waters20,24,25,26,27. All sea turtle species are listed as Vulnerable, Endangered, Critically Endangered, or Data Deficient by the IUCN Red List (Accessed: 16 May 2025)28,29, are protected under Appendix I of CITES (Accessed: 16 May 2025), and are listed in Schedule I of the Indian Wildlife Protection Act (1972 & 2023), granting them the highest legal protection in India30,31.

India’s 11,098.81 km coastline32 offers diverse nesting habitats for sea turtles. Except for Caretta caretta, all four species nest along the Indian coast24,26. Among these, Lepidochelys olivacea is the most abundant and widely nesting species throughout India33,34. This species is known for its spectacular mass nesting behaviour, or arribadas, along Odisha’s Rushikulya and Gahirmatha beaches35,36. All species nest along India’s islands11,13,15,24,26,37,38, with Eretmochelys imbricata and Dermochelys coriacea predominantly nesting on the Andaman, Nicobar, and Lakshadweep islands39,40,41,42. Chelonia mydas nests along the Gujarat and Tamil Nadu coasts33, while occasional D. coriacea nesting occurs along Tamil Nadu and Karnataka33,43,44.

Lepidochelys olivacea is the only confirmed nesting species along Karnataka’s coast, with historical records18,19,33,43,45. Local testimonies suggest possible nesting of Chelonia mydas off Honnavar43,46. Nesting typically occurs at night, during high tide, and often coincides with the lunar cycle, from September through June, primarily on estuarine sandy beaches near river mouths10,11,12,14,26,46,47.

Sea turtles face numerous threats, including coastal development and beach erosion leading to habitat loss, artificial illumination, plastic pollution, poaching, unsustainable fishing practices, accidental capture in fishing gear, entanglement in ghost nets, and diseases or parasites2,3,11,15,18,38,48,49,50,51,52. In Karnataka, mass nesting activities previously documented at hatchery sites such as Jali (Uttara Kannada), Maravanthe (Udupi), and Bengere (Dakshina Kannada) have declined significantly since the 1980s19,24,43,45,46,53. With limited monitoring conducted in recent decades, there remains a critical gap in understanding the current status of L. olivacea nesting along the Dakshina Kannada coastline.

This study aims to identify Lepidochelys olivacea nesting activity along the Dakshina Kannada district, where documentation is scarce in recent years. The research provides a baseline dataset to help establish a robust conservation action plan in the region. This study is essential for tracking species recovery and informing targeted interventions amid growing anthropogenic pressures on marine biodiversity. Specifically, the study aimed to: (1) identify and document nesting locations along the study area; (2) map and analyse spatial and temporal patterns of nesting activities; and (3) evaluate hatching and emergence success rates of nests recorded during the study period. Considering the data shortfall of turtle nesting, this study provides critical baseline data necessary for the future conservation and management of sea turtle populations in this region.

Results

Historic records

Earlier records indicate that Lepidochelys olivacea nesting activity was observed and documented across various beaches along the Dakshina Kannada coast (Fig. 43). A significant hatchery site was previously established at Bengere–Tannirbhavi Beach, located at the current exit point from the Tannirbhavi Tree Park to the beach (Figs. 2 and 3). This hatchery was one of the major conservation sites in the region, with numerous nesting events historically recorded along Bengere Beach (Fig. 1).

Fig. 1
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Historic nesting beaches (Location source –19. Map generated by the authors using ArcMap v10.4 (ESRI, Redlands, CA, USA; https://www.esri.com).

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Fig. 2
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Old hatchery in Bengere-Tannirbhavi beach (Location source –43,46. Map generated by the authors using ArcMap v10.4 (ESRI, Redlands, CA, USA; https://www.esri.com).

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Fig. 3
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Location of the old hatchery that is currently Thannirbhavi tree park exit to the beach (Location credits: Grandson of the old hatchery monitoring fisherman).

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Nesting observation

Olive Ridley turtle (Lepidochelys olivacea) nesting along the Dakshina Kannada coast was documented during this study. To assess recent nesting trends and local ecological knowledge, semi-structured interviews were conducted with community members, primarily fishers, during the initial phase of the study. Respondents reported that nesting had not been observed for a period ranging from 2 to 20 years. Specifically, 35% (n = 7) of interviewees stated that they had not witnessed any nesting events in the past 20 years, while 30% (n = 6) reported the absence of nesting over the past 15 years. An additional 15% (n = 3) mentioned that nesting had last been observed approximately five years ago. Interestingly, 20% (n = 4) of the respondents indicated having witnessed nesting activity within the past two years, suggesting a possible resurgence of nesting along this coastline (Fig. 4).

Fig. 4
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Interview survey showing the number of years’ gap from earlier nesting witnessed by the local fishing community.

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Nesting season and temporal distribution

The first confirmed nesting event was documented on 31 st December 2023 at Sasihithlu Beach. The Olive Ridley sea turtle (Lepidochelys olivacea) exhibited a sporadic nesting pattern along the Dakshina Kannada coast, with the season extending from December 2023 to March 2024. Nesting activity peaked in February, accounting for 52% (n = 11) of the total recorded nests, followed by January with 29% (n = 6). Nesting was minimal in December (5%, n = 1) and declined again in March, during which 14% (n = 3) of the nests were documented (Fig. 5).

Fig. 5
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Nests discovered over the nesting season.

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Spatial distribution

A total of 21 Olive Ridley turtle nests were discovered, reported, and protected across six beaches within the study area. The highest concentration of nests was observed at Sasihithlu Beach, accounting for 62% (n = 13) of the total. This was followed by Bengere Beach with 14% (n = 3), and Tannirbhavi Beach with 9% (n = 2). The remaining nests were distributed equally among Panambur, Kuli, and Iddya beaches, each contributing 5% (n = 1) to the total nest count (Figs. 6 and 7).

Fig. 6
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Total number of nests protected across the beaches in the Dakshina Kannada district.

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A total of 62% (n = 13) of nests were protected at Sasihithlu Beach, specifically in Transects SST-1 and SST-2. This was followed by the Bengere region, where three nests were recorded in Transects BT-1, BT-2, and BT-3. Additional nests were documented and safeguarded at Tannirbhavi Beach (Transect TT-1), Panambur Beach (Transect PT-1), Kulai Beach (Transect HT-1), and Iddya Beach (Transect HT-2) (Fig. 7).

Fig. 7
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Nesting sites located along the Dakshina Kannada Coast, Karnataka. Map generated by the authors using ArcMap v10.4 (ESRI, Redlands, CA, USA; https://www.esri.com).

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Lunar nesting time frame

During the study, nesting occurred across various lunar phases, ranging from high illuminated Full Moon and the Waxing Gibbous phases (e.g., Nest No. 16 with 100% illumination and Nest No. 7 with 95%) to low illumination during Waxing and Waning Crescents (e.g., Nest No. 2 with 1% illumination and Nest No. 20 with 5%). Nesting observed in the low illumination phase suggests a deviation from earlier recorded research, where it was suggested or stated that sea turtles nest during the full moon phase. The observations are deviating from earlier research (Fig. 8).

Fig. 8
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Moon phase and the number of nests identified during the moon phase.

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The distribution of nests along illumination ranges highlights changes in nesting behaviour. The highest nesting activity occurs at 0–10% and 91–100% illumination (n = 4), followed by 51–60% range (n = 4), and the 21–30% range (n = 3) shows moderate activity. Minimal activity was observed in the 11–20% and 71–80% illumination ranges (n = 1), and no nests were recorded in the 61–70% range (Fig. 9).

Fig. 9
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Graph showing the Lunar illumination range % against the number of nests.

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Nesting density

The average nesting density along the coast is 1.16 nests/km, with the highest nesting density observed at Sasihitlu Beach (Haleangadi), with 13 nests along a 5.52 km stretch, yielding 2.36 nests/km, highlighting its ecological significance as a key nesting habitat. Kulai Beach exhibited a relatively high nesting density of 1.30 nests/km despite being the shortest stretch surveyed (0.77 km). Panambur Beach reported a comparable density of 1.02 nests/km with one nest along a 0.98 km stretch. Bengere Beach recorded three nests over 2.65 km, resulting in a moderate density of 1.13 nests/km. Conversely, Iddya Beach (Surathkal) and Tannirbhavi Beach exhibited lower densities of 0.88 nests/km and 0.31 nests/km, respectively, with the latter being the longest beach surveyed (6.38 km) (Fig. 10).

Fig. 10
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The bar graph represents nesting density across the study area.

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Clutch characteristics

The total number of eggs in a clutch ranged from 71 to 135 (n = 19) with an average of 100. Foxes predated two nests identified along the Taneerbavi beach, and their relocated clutch of eggs was 17 and 30 (n = 2).

Egg characteristics

The eggs are spherical, with a leathery texture and milky white colouration, weighing approximately 31.5 g and measuring about 38.03 mm in diameter. A positive correlation was observed, suggesting that heavier eggs generally have larger diameters. This trend was further supported by regression analysis, which revealed an upward trajectory between the two variables (Fig. 11).

Fig. 11
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Relationship between egg weight and diameter.

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Incubation period analysis

The incubation periods of 17 nests ranged from 45 to 53 days, with a mean duration of 49.9 (SD ± 2.28) days. The most commonly observed incubation period was 49 days, recorded in 7 nests out of the 17 nests (Fig. 12). This clustering suggests a consistent developmental window during the core nesting season. Most nests incubated for 49 to 51 days, with shorter durations generally associated with nests laid later in the season. The shortest incubation period (45 days) was recorded for Nest DK-14, laid in mid-February, while the longest (53 days) was observed in DK-01, laid at the beginning of the nesting season on 31 December 2023 (Fig. 13). Overall, a declining trend in incubation duration was observed from January to March of the study period.

Fig. 12
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Incubation period distribution.

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Fig. 13
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Incubation period divided among the individual nests.

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In situ and relocated nest analysis

A total of 21 nests were recorded across six beaches in Dakshina Kannada. Of these, 62% (n = 13) were conserved in situ, while 38% (n = 8) were relocated to safer locations (Fig. 14). Sasihithlu Beach accounted for the highest number of clutches (n = 13), with 38% (n = 5) conserved in situ and 62% (n = 8) relocated due to their proximity to the high-tide line (HTL). Solitary clutches recorded at Iddya and Kulai Beaches were retained in situ. At Tannirbhavi Beach, three clutches were recorded; two were relocated from high-tide zones, while one was preserved in situ. Panambur Beach had one clutch, which was relocated due to disturbances associated with commercial activity. At Bengere Beach, two clutches were recorded, and both were relocated due to the risk of tidal inundation. Among all relocated nests, 92% (n = 12) were moved due to their closeness to the HTL, while 8% (n = 1) were relocated because of anthropogenic pressure (Fig. 15).

Fig. 14
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Chart showing the number of nests relocated and the number of nests protected in situ.

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Fig. 15
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Threats leading to relocation.

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Distance from high tide line

At Sasihitlu Beach, clutches were located between 4.3 m and 16 m from the high-tide line and within 0.48–2.27 km of the Shambhavi and Pavanje Estuary. The single clutch on Iddya Beach was positioned 6 m from the high-tide line, proximal to multiple estuarine systems, including the Hosahitlu Sea Walk Breakwater and the New Mangalore Port. At Taneerbavi Beach, the conserved clutch was situated 22 m from the high-tide line and 3.5 km from the Gurupura Estuary. The solitary clutch at Kulai Beach was found closer to the river mouth, with distances ranging from 0.39 km (Hosahitlu Sea Walk Breakwater) to 13.69 km (Gurupura Estuary) (Fig. 16).

Fig. 16
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Distance from High tide line for relocated nests.

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Hatching success

A total of 1,957 eggs were recorded across all protected nests. Of these, 33% (n = 955) successfully hatched, and 32% (n = 928) (Fig. 17) of the hatchlings were released into the sea (Fig. 18). Among the hatched eggs, 1% (n = 27) hatchlings were found dead within the nests. Additionally, 34% (n = 1,002) of the eggs remained unhatched, 28% (n = 815) were affected by fungal growth, and 6% (n = 187) were identified as underdeveloped embryos (Table 1). The average hatching success rate across all sites was 45.84%, while the emergence success rate stood at 34.26%.

Fig. 17
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Nest survey across the study area.

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Fig. 18
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Hatchlings being guided into the sea.

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Table 1 Overall nest survey.
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Correlation of emergence success between in situ and relocated hatching

In situ nests had a higher hatching success rate of 58.93%, whereas relocated nests exhibited a lower success rate of 37.79%. Similarly, emergence success was greater in situ nests (41.17%) than in relocated nests (30%). The overall hatching success was 57.2%, and the emergence success was 42.8% (Fig. 19).

Fig. 19
figure 19

Hatching success and emergence success between in situ and relocated conserved nests.

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The overall average hatching success was higher for in situ nests (59%) compared to relocated ones (32.69%), several individual relocated nests such as DK-6 (98%), DK-3 (84.4%), and DK-1 (76.99%) that was comparatively better than many in situ nests (Fig. 20).

Fig. 20
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Hatching success difference between certain specific nests relocated and in situ.

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Hatchling morphometry

A total of n = 248 hatchlings were measured using a vernier calliper and a gram weighing scale. The overall average weight was 17.29 g. The Straight-line Carapace (SCL) was 41.87 mm, (Dorsal view Fig. 22) and the Straight-line Carapace Width (SCW) was 32.68 mm (Venteral view Fig. 21).

Fig. 21
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L. olivacea hatchling ventral view.

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Fig. 22
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L. olivacea hatching dorsal view.

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Correlation between hatching success, emergence success, and nest depth

A moderate positive correlation (r = 0.415) between hatching success and nest depth, suggesting that deeper nests tend to have higher hatching success rates. Although the p-value of 0.061 did not meet the conventional threshold for statistical significance (p < 0.05), the result suggests a trend worth further exploration. A slope of 2.87 with an intercept of −136.40, indicating that for each additional centimetre in nest depth, hatching success increased by approximately 2.87% points. The model explained approximately 17.3% of the variation in hatching success (R2 = 0.173) (Fig. 23).

The relationship between nest depth and emergence success revealed a weak positive trend, where greater nest depth was associated with slightly higher emergence success (coefficient = 1.36). This relationship was not statistically significant (p = 0.132), and the model explained only 16.6% of the variability in emergence success (R2 = 0.166) (Fig. 24).

Fig. 23
figure 23

Relationship between nest depth and hatching success.

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Fig. 24
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Relationship between nest depth and emergence success.

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Regression model of hatching success and distance from river mouth

A total of eight in situ nests from four beaches were analysed. The hatching success ranged from 18.42% to 90.24%, with an average of 59.8%. A clear trend was observed: nests situated closer to the river mouth, particularly within 0.39 km to 1.2 km, showed significantly higher hatching success, often exceeding 70%. For example, nests DK-2, DK-14, and DK-20, located at 1.2 km, 0.48 km, and 0.39 km, respectively, had hatching success rates of 90.24%, 87.32%, and 70% (Fig. 25).

Nests located farther from the river mouth (≥ 2.26 km) exhibited lower success, with DK-7 and DK-4 achieving only 41.17% and 47.32%, respectively. The lowest success (18.42%) was observed at DK-9, the nest located farthest from the river mouth at 3.5 km.

Fig. 25
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Regression model to show the relation between distance from the river mouth and hatching success in in situ conserved nests.

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Localised threats to nests and nesting beaches

Coastal development

Beach erosion is a natural phenomenon occurring due to intense wave action caused by tidal shifts, monsoons, cyclones, and changing climatic conditions. To prevent erosion, man-made structures or barriers are created, some of them being seawalls, groynes, jetties, and other forms of beach armouring constructed along many coastlines. These structures have helped prevent erosion temporarily, but have altered the beaches and hence the nesting sites of Lepidochelys olivacea along this coast. One of the most significant threats observed in the study area was coastal development. This has had a significant impact on beach erosion, resulting in the gradual loss of major nesting habitats. Locations such as Sasihithlu, Iddya, Panambur, and Bengere are currently impacted by sea wall constructions, with prominent seawall structures to facilitate a fishing harbour in Kulai, which was constructed between 2022 and 2023. This stretch may have previously supported viable nesting activity, especially considering that Iddya Beach, where nesting was recorded this season following the last reported sighting by locals in 2022 (Figs. 26, 27, and 28).

Historic records show that Ullal, Someshwar, and Batampady beaches as former nesting hotspots. However, no nests were reported in these areas during the current nesting season. A possible explanation is the installation of offshore rock-revet structures, which, although situated a few kilometres from the shoreline, may be deterring sea turtles from approaching their natal beaches. Additionally, Ullal’s T-shaped groynes, resembling those in Padukere (Udupi district), have triggered severe beach erosion, further reducing the availability of nesting beaches (Figs. 29, 30, and 31).

Fig. 26
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Satellite image taken from Google Earth of Kulai beach in 2022. Satellite imagery obtained from Google Earth (© Google, accessed 1 st June 2025) and processed by the authors using Google Earth’s mapping tools.

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Fig. 27
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Satellite image from Google Earth of the same beach with sea wall being constructed in 2023–2024. Satellite imagery obtained from Google Earth (© Google, accessed 1 st June 2025) and processed by the authors using Google Earth’s mapping tools.

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Fig. 28
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Satellite image taken from Google Earth of the same beach with the completed sea wall in the current year (2025). Satellite imagery obtained from Google Earth (© Google, accessed 1 st June 2025) and processed by the authors using Google Earth’s mapping tools.

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Fig. 29
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Ullal beach before construction of beach armouring in 2019. Satellite imagery obtained from Google Earth (© Google, accessed 1 st June 2025) and processed by the authors using Google Earth’s mapping tools.

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Fig. 30
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Ullal T-shaped groynes construction in 2020. Satellite imagery obtained from Google Earth (© Google, accessed 1 st June 2025) and processed by the authors using Google Earth’s mapping tools.

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Fig. 31
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Ullal T-shaped groynes in 2025. Satellite imagery obtained from Google Earth (© Google, accessed 1 st June 2025) and processed by the authors using Google Earth’s mapping tools.

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Offshore rock-rivet structure in Ullal was constructed between 2017 and 2018 (Fig. 32), while a second offshore structure near Batampady Beach was installed in 2021 (Fig. 33).

Fig. 32
figure 32

Satellite images showing the sea armouring construction in Ullal and Talapady. Satellite imagery obtained from Google Earth (© Google, accessed 1 st June 2025) and processed by the authors using Google Earth’s mapping tools.

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Fig. 33
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Satellite images showing the sea armouring construction in Ullal and Talapady. Satellite imagery obtained from Google Earth (© Google, accessed 1 st June 2025) and processed by the authors using Google Earth’s mapping tools.

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Unsustainable fishing practices

Fishing activities near the nesting grounds have significantly affected nesting female turtles, which are often accidentally captured in fishing nets or injured through collisions with vessels, frequently resulting in severe injuries leading to mortality. Entanglement in ghost fishing gear is an additional threat, with numerous entangled ghost net bundles observed washed ashore along the study area (Fig. 34 Fig. 35). This indicates the likely presence of abandoned nets in nearshore waters, posing a persistent threat to nesting sea turtles, hatchlings, and other marine species.

Fig. 34
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Entangled ghost fishing gear washed ashore at Bengere.

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Fig. 35
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Entangled ghost fishing gear washed ashore at Iddya.

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A major fishing harbour located at Bengere supports fishing operations along the Dakshina Kannada coast. During the study period, various fishing practices, including light fishing, bull trawling, and nearshore fishing, were observed.

On 23 January 2024, a deceased female Lepidochelys olivacea was discovered washed ashore at the Sasihithlu nesting site. Post-mortem analysis revealed the presence of 59 fully developed eggs. The cause of death was determined to be head trauma, likely resulting from a collision with a rock or a fishing vessel (Figs. 36 and 37).

Fig. 36
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L. olivacea stranded at Sasihithlu beach.

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Fig. 37
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developed eggs found in the stranded turtle during necropsy.

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Anthropogenic pressures on nesting beaches

Human activity has been predominantly observed at an accelerated rate throughout the study area. Recent data from 2023 indicates that Panambur and Tannirbhavi beaches are among the most frequently visited tourist destinations in Dakshina Kannada, receiving an estimated 3,500 to 4,000 visitors daily54. Tannirbhavi is also proposed to be a Blue Flag Beach55.

Despite this high level of human presence, nesting activity continues to occur at both beaches. These locations as potential models for eco-tourism development, where conservation and recreation can coexist with proper management and community involvement.

Artificial illumination

Artificial illumination is a significant threat to sea turtle hatchlings, which rely on natural light cues to navigate toward the sea after emerging from their nests. During the study, all nesting beaches were observed to have varying levels of artificial lighting, particularly from streetlights, commercial establishments, and nearby infrastructure (Fig. 38). This unnatural light often disorients hatchlings, causing them to move inland or parallel to the shore instead of heading toward the ocean. Such disorientation increases the risk of predation, dehydration, and mortality, ultimately reducing hatchling survival rates.

Fig. 38
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Artificial illumination in Panambur beach.

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Beach pollution

Plastic and beach pollution are critical threats to nesting sea turtles and their hatchlings. Waste, especially plastics of all materials, fishing nets, Styrofoam, medical waste, footwear, glass bottles, as well as shattered glass fragments, and other synthetic debris (Fig. 39). They can obstruct nesting females from reaching suitable nesting sites or cause them to abandon their nesting attempts in the area, forcing them to find a new nesting ground elsewhere. For hatchlings, navigating through the debris increases the risk of entanglement, injury, or exhaustion, reducing their chances of survival.

Fig. 39
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Beach pollution in Bengere beach, which is a nesting beach.

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Natural predators

Natural predators, such as pelagic birds, crabs, and foxes, are observed throughout the region, with foxes particularly found at Tannirbhavi Beach, where they have been documented preying on one of the nests. Another significant threat to both nests and nesting sea turtles is feral dogs. They pose a considerable risk to nesting sea turtles, their nests, and hatchlings. Feral dogs are known to attack nesting turtles, preventing them from nesting on the beach (Fig. 40). Feral dogs are also known to destroy nests and feed on hatchlings as they emerge, further exacerbating the threat to sea turtle populations.

Fig. 40
figure 40

Feral dogs on Sasihithlu beach.

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Discussion

The present study provides the first confirmed documentation of Olive Ridley (Lepidochelys olivacea) nesting activity along the Dakshina Kannada coast since 200219, marking a significant milestone in the species’ conservation in this region after an 18-year gap. Historically, this coastline supported substantial nesting activity, particularly around Bengere–Tannirbhavi, where a major hatchery was once operational19,43,46. However, a decline in L. olivacea nesting led to the discontinuation and demolition of the old hatchery. The recent reappearance of nesting activity over the past two decades suggests a potential resurgence influenced by natural nesting behavior and incentive-based nest reporting programs56,57,58. Consistent with previous studies, sporadic nesting of L. olivacea continues along the Dakshina Kannada coast19,43,46,59.

Nesting activity was recorded between December and March, peaking in February, contrasting with earlier studies: Frazier46 reported a nesting season from August to April; Sharath19,43 documented nesting primarily in September–October; and McCann59 observed nesting from September to February along Udupi and Dakshina Kannada coasts. These temporal shifts may reflect climate change effects, potentially causing a gradual delay in the nesting season21,60,61, warranting further investigation.

Nesting seasons in other regions, such as Odisha during Arribadas, span January–April13, which aligns with patterns reported from December–May in various locations13,15,24,26,33,37. Historically active nesting sites along the Dakshina Kannada coast include Sasihithlu, Panambur, Bengere, Tannirbhavi, and Ullal19,43,46. In the present study, Sasihithlu Beach recorded the majority of nests (n = 13), accounting for 62% of total nests, likely due to favourable geomorphology and lower human disturbance. Interestingly, nesting was also observed on high-traffic beaches such as Panambur and Tannirbhavi, indicating a tolerance to moderate anthropogenic pressures. Sites like Ullal and Someshwar showed no nesting activity, likely due to coastal modifications and beach erosion62.

Nesting occurred across a broad range of lunar illumination (0–10% to 91–100%), challenging the traditional assumption of full-moon preference and possibly reflecting behavioural adaptation to artificial light, altered beach profiles, or predator pressures48. Reduced false crawls and nesting within 4.3 m of the high tide line underscore the threats to nests and the urgent need for early detection and well-planned relocation strategies. Clutch sizes ranged from 71 to 135 eggs (mean 100 eggs), with a strong correlation between egg weight and diameter, suggesting maternal investment strategies that may enhance hatchling fitness. Incubation durations ranged from 45 to 53 days (mean 49.9 ± 2.28 days), with shorter durations in warmer months. Nest depth was moderately positively correlated with hatching success (r = 0.415) and weakly positively correlated with emergence success, highlighting the benefits of deeper nests for clutch survival. In situ nests exhibited higher hatching (58.93%) and emergence (41.17%) success compared to relocated nests (37.79% and 30%), although some relocated nests performed exceptionally well, emphasizing the importance of site-specific conditions17,63. Nests closer to river mouths showed higher hatching success, indicating more favourable environmental conditions for natural incubation.

Coastal development poses one of the most significant threats to nesting habitats along the study area, causing rapid erosion and habitat degradation. Seawall and beach armouring at Sasihithlu, Iddya, Panambur, and Bengere, along with offshore structures near Ullal and Batampady, are altering beach morphology, reducing available nesting beaches. Historically active nesting sites such as Ullal, Someshwar, and Batampady recorded no nesting during this season62. Additionally, intensive fishing activity, supported by the Bengere harbour, further threatens nesting success, evidenced by the incidental death of a nesting L. olivacea and the presence of ghost nets.

Despite these challenges, nesting was documented across six beaches, highlighting both the species’ resilience and the positive impact of ongoing conservation interventions, including beach patrolling, public outreach, incentive-based nest protection, and targeted surveys56,57,58.

Conclusion

The return of nesting activity, particularly in highly disturbed areas, reflects both the resilience of Lepidochelys olivacea and the impact of conservation measures. The findings underscore the need for habitat protection, artificial light regulation, fishing regulation, discarded gear management, and continued engagement with local communities. In addition, further research on nesting beaches, nest dynamics, behavioural studies, climate change influence on sea turtles, and threat analysis has to be carried out to create a robust conservation action plan and policies.

These results contribute valuable baseline data for further research, long-term monitoring, and policy formulation. This study marks the first confirmed nesting report since 2002, indicating that the Dakshina Kannada coast is a potential nesting ground that requires protection. The incentive program played a vital role in rediscovering nests and reducing poaching. The variability in lunar nesting behaviour suggests that Lepidochelys olivacea in this region exhibits adaptive nesting strategies, potentially influenced by artificial illumination on nesting beaches. Continued research and monitoring is essential to understand the impact of artificial lighting, climate change impact, temperature influence, and anthropogenic pressures.

The re-emergence of Lepidochelys olivacea nesting along Dakshina Kannada is a conservation success story driven by community engagement and vigilant fieldwork. These findings emphasise the need for adaptive seasonal management, continued habitat conservation, and long-term ecological monitoring. With robust policy and public support, this coastline can once again become a secure nesting ground for sea turtles.

Methods

Study area

This study examines and records the nesting patterns of Lepidochelys olivacea along the Dakshina Kannada (Mangalore) district coast of Karnataka, from Haleangadi to Talapady, covering approximately 36.66 km32 and including around 40 beaches ranging from commercial to rural and uninhabited (Fig. 41). An assessment by the National Centre for Coastal Research (NCCR) indicates that nearly 48.4% of this coastline underwent erosion between 1990 and 201864. The region hosts rich marine biodiversity and is characterised by two major river estuarine mouths, the Pavanje and Shambhavi, which separate Dakshina Kannada and Udupi districts, dividing Sasihithlu Beach and Hejmadi Beach. The coastline supports significant fishing activities, including a major fishing harbour and the New Mangalore port54. Coastal engineering structures such as beach armouring and offshore rock formations have contributed to beach erosion, reducing the availability of suitable nesting habitats. In 2023, the diversion of the Pavanje and Shambhavi river mouths through a newly constructed jetty at Hejmadi further altered coastal dynamics, potentially impacting sea turtle nesting sites62.

Fig. 41
figure 41

Study area of beaches along the Dakshina Kannada district. Map generated by the authors using ArcMap v10.4 (ESRI, Redlands, CA, USA; https://www.esri.com).

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Fig. 42
figure 42

Transacts covering the beaches along the study area. Map generated by the authors using ArcMap v10.4 (ESRI, Redlands, CA, USA; https://www.esri.com).

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Survey method

Questionnaire surveys were carried out during the pilot study to raise awareness among fishing communities and identify potential sea turtle nesting grounds10. Infographics emphasising conservation importance and a hotline for reporting nests were distributed, alongside structured interviews with fishermen (n = 20). In Dakshina Kannada, the Mangalore Forest Department Marine Cell conducted awareness campaigns, beach clean-ups, and community outreach, and introduced an incentive-based conservation program offering Rs. 5000 for nest reporting and protection to local fishing communities56,57,58,65,66. Collaborative beach clean-ups with local schools and colleges included awareness sessions and door-to-door community engagement activities63,67. Similar activities were conducted in the Udupi district, and information on potential nesting grounds was shared with the respective forest departments. The study spanned two nesting seasons (December 2023–March 2024 and December 2024–March 2025) with necessary permissions (No. PCCF(WL)/E2/CR-71/2023-24) from the Karnataka Forest Department, under the Wildlife Protection Act (1972)30.

Transects (~ 2–3 km) were established across open beaches with minimal erosion or armouring (Fig. 42). Night patrols and morning walks were undertaken to detect nests through body pits, crawl marks (Fig. 43), and sand disturbance. Nests were confirmed by carefully locating the first egg (Fig. 44). At each site, data on GPS location, distance from the high tide line (HTL), vegetation proximity, river mouth proximity, and human threats were recorded2. Additionally, to analyse changes in nesting patterns in relation to lunar phases, the phases of the moon corresponding to each nesting event were documented using data from www.moongiant.com.

Fig. 43
figure 43

L. olivacea tracks.

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Fig. 44
figure 44

Natural nest in Sasihithlu beach opened to be relocated.

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Fig. 45
figure 45

Nest fenced and protected by the forest department.

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Nests threatened by tidal action, human pressure, or predation were relocated further inland along the same beach, within 10 h following established protocols38,40,67, wherein safer nests were fenced for in situ conservation (Fig. 45). Relocation of nests in the case of threats has proven worldwide to be an effective conservation measure33,38. During relocation, the depth to the first egg, total nest depth, number of eggs, and relocation distance were recorded. Once relocated, the nests were fenced using a mesh to prevent predators and poaching of the clutch67,68. Additionally, motion-sensor cameras were installed to enhance response times during hatchling emergence. The protected nests were monitored daily from day 45 until hatching (up to day 60). Once the hatchlings emerged (Fig. 46), they were placed in tubs to be released to the sea (Fig. 47). Post-hatching nest excavations recorded unhatched eggs, dead hatchlings, infertile eggs, and live hatchlings, enabling calculation of hatching and emergence success19,43,46,62,69. Statistical analyses were performed using Excel and Google Sheets for nesting surveys, lunar time frame, hatching and emergence success, and Python via Google Colab to evaluate relationships among nest depth, nest density, hatching success, emergence success, regression models, and incubation duration. Additionally, observations on the timing of nesting events relative to lunar phases were recorded to assess behavioural trends in nesting synchrony.

Fig. 46
figure 46

L. olivacea hatchlings emerging from the nest.

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Fig. 47
figure 47

Hatchlings placed in tubs ready to be released.

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Throughout the study, no turtles, eggs, or hatchlings were harmed, mishandled, or exploited, and all research activities were carried out under the supervision of Forest Department personnel.