Green turtles, Chelonia mydas, are among the most ecologically important marine megafauna on the planet. Adult turtles graze on seagrass meadows, keeping these underwater pastures healthy, while the animals themselves serve as prey, hosts, competitors and even apex predators within marine food webs. Seven species of sea turtles exist worldwide, and Malaysia hosts nesting by five of them, including the green turtle, known locally as penyu agar or penyu hijau. The species is the most widely distributed sea turtle in the country, with nesting recorded in Sabah, Sarawak, Terengganu, Perak, Pahang and Johor. At the well-known Sabah Turtle Islands, annual nest counts can reach 15,000, and Redang Island records between 700 and 1,500 nests each year.

Similajau National Park tells a very different story. Gazetted in 1976 and spanning 89.96 square kilometers, the park protects golden sandy beaches, mixed dipterocarp forests and kerangas woodlands, along with endemic primates such as the Bornean banded langur and Hose’s surili. Its four main nesting beaches, Chalet Beach, Turtle Beach 1, Turtle Beach 2 and Golden Beach, have never received the scientific attention lavished on Sarawak’s flagship rookeries like Talang-Satang National Park. Records kept by rangers of the Sarawak Forestry Corporation, who patrol the high tide lines looking for flipper tracks, formed the raw material for the new analysis, which covered the years 2015 to 2017 and 2022 to 2024. Years with missing records, including 2018 and the pandemic closure period of 2019 to 2021, were deliberately excluded to avoid mistaking absent data for absent turtles.

The headline numbers are stark. Across the study years, nesting activity was low and inconsistent, averaging just 3.33 nests per year, with annual totals ranging from zero to six. In 2023, despite routine patrols, no green turtle nesting was confirmed at all. The mean hatching success rate across the study period was 45.47 percent, swinging from a low of 24 percent in 2016 to a high of 90 percent in 2022. For comparison, Talang-Satang National Park records more than 2,000 nests annually, Redang Island up to 2,500, and the Sabah Turtle Islands as many as 15,000. Against those benchmarks, Similajau is a footnote in Malaysian sea turtle reproduction, but a footnote that conservationists cannot afford to ignore.

The year 2024 offered the most detailed window into the park’s reproductive biology, because that was the first year clutch-level data were recorded. Four nests on Chalet Beach were discovered and successfully relocated to the park’s roofed, fenced and elevated hatchery. Clutch sizes ranged from 119 to 137 eggs, averaging 129.75 eggs, a figure that sits comfortably within the range reported for green turtles elsewhere in Malaysia and beyond, such as 42 to 150 eggs per clutch in Negeri Sembilan and 74 to 179 in the Chagos Archipelago. Because clutch size generally correlates with female body size, the authors suggest, cautiously, that the females nesting at Similajau may be relatively large, older remigrant individuals, though no tagging or morphometric data were available to confirm this.

The fate of those four nests revealed how precarious reproduction is at the site. Apparent incubation durations ranged from 54 to 62 days, averaging 58.5 days, which is comparable to the roughly 60-day incubation period typical of sea turtles and hints that nest temperatures probably fell within a generally suitable range. But hatching success varied enormously, from a catastrophic 7.69 percent in the first nest to 73.11 percent in the fourth, averaging 41.8 percent with a standard deviation of 26.8. The first nest had been inundated by seawater before it was relocated, and its detection came up to five days after oviposition because of a patrol gap. When researchers excavated the nests after emergence, approximately 95 percent of the unhatched eggs showed no embryonic development at all, a pattern consistent with early mortality caused by flooding, osmotic stress and reduced oxygen availability in waterlogged sand.

Nest relocation itself is a double-edged sword. Moving eggs is standard practice when in-situ nests face near-certain destruction from predators, tidal flooding or human disturbance, and at Similajau the threats are real: ghost crabs, macaques, feral pigs, monitor lizards, ants and fungal infections are all documented in Malaysia and present in the park. But timing matters enormously. Relocation is ideally performed within one to two hours of oviposition, before the yolk sac membrane attaches to the shell, and although it can be done within 12 hours, hatching success declines significantly. At Similajau, remote beaches and irregular patrol coverage mean nests are often found too late for optimal handling, and broken eggs during relocation, six in one nest and nine in another in 2024, further eroded output. The study also notes that a metal pole used to locate eggs within nest pits can break eggs at the top of the clutch.

The 2024 season also exposed the difficulty of simply counting what happens on the beach. Rangers detected 20 nest pits that year, but only four could be confirmed as successful nests with eggs. Five pits were surrounded by scattered predated eggshell remnants, evidence that eggs had been laid and then eaten, while the remaining 11 showed no clear evidence of oviposition and may have been abandoned nesting attempts. Because the pits were clustered close together, it was impossible to determine whether the eggshell fragments represented separate nesting events or the remains of a single clutch dragged apart by wildlife, rain or tides. The authors argue that estimating true nest numbers from eggshell fragments alone is unreliable on beaches inhabited by diverse fauna and continually reshaped by waves and sediment movement.

Why is Similajau so quiet compared with other Malaysian rookeries? The study points to a possible historical legacy: mass mortality events in the 1990s, when roughly 100 sea turtle carcasses were recorded annually along Sarawak’s coasts, largely attributed to illegal trawling in key foraging areas, migratory routes and inter-nesting habitats. Given how far green turtles roam across Sarawak waters, the turtles that once nested at Similajau may have been caught up in those losses. Ongoing pressures compound the problem, from habitat degradation, climate change, egg and meat poaching, fisheries bycatch and ghost nets to unsustainable tourism, marine debris entanglement and vessel strikes. Because green turtles mature late and live long, any recovery in nesting activity will be slow and will require sustained intervention.

The researchers are careful about the limits of their work. The dataset is small and fragmented, patrol coverage varied from daily monitoring on Chalet Beach to monthly visits elsewhere, and records of survey effort over the years were unavailable, so the true nesting frequency could be higher than the counts suggest. No incubation temperatures were recorded, fungal infection of unhatched eggs was not examined, and the emergence success of hatchlings was never measured, though supervised releases mean it probably resembled hatching success. What the study delivers instead is a baseline, the first quantitative characterization of a nesting population that had previously gone unmeasured. The authors recommend intensified patrols during peak nesting periods, faster relocation to minimize embryo mortality, possible in-situ protection with predator exclusion or shading for low-risk nests, expanded surveys of nearby beaches, and community-based monitoring involving local stakeholders, conservation groups and university volunteers. They also call for research into the environmental drivers of reproductive output, including temperature, humidity and microbial infection. The reappearance of nesting at Similajau since 2015 is encouraging, they conclude, but the low and inconsistent numbers make clear that this quiet corner of Borneo will need decades of attention if its green turtles are to endure.

Subject of Research: Green turtle nesting activity and reproductive output at Similajau National Park, Sarawak

Article Title: Nesting activity and reproductive output of green turtles in Similajau National Park, Bintulu, Sarawak

Article References: Ting Jia Lei, A., & Hassan, R. B. (2026). Nesting activity and reproductive output of green turtles in Similajau National Park, Bintulu, Sarawak. Frontiers in Amphibian and Reptile Science, 4, Article 1890215. https://doi.org/10.3389/famrs.2026.1890215

Image Credits: AI Generated

DOI: 10.3389/famrs.2026.1890215

Keywords: green turtle, Chelonia mydas, Similajau National Park, Sarawak, nesting activity, hatching success, nest relocation, embryo mortality, sea turtle conservation, Malaysia, marine megafauna, hatchery management

The original tagging operation took place at 4:57 a.m. on 27 August 2021, on a nesting beach at Breem Island (25.62 N, 36.50 E), an island within the lagoon where The Red Sea Project, one of Saudi Arabia’s large-scale coastal development initiatives, is being built. At the time of first capture, the turtle’s curved carapace length, measured from the notch to the tip of the shell, was 100.7 centimeters. The satellite tag, a Wildlife Computers Platform Terminal Transmitter with the code 200112, tracked her for 212 days, revealing a remarkable journey that connected two countries across the northern Red Sea.

After completing her nesting activity, the turtle departed Breem Island and swam roughly 19 days to a foraging ground inside Wadi el Gemal National Park in Egypt, arriving on 15 September 2021. She then remained resident within that Egyptian feeding area for the next 197 days, with her home range and core area of use mapped in detail by the tracking data. The route confirmed what earlier satellite tracking studies had suggested: the Saudi Arabian Red Sea serves as a critical migratory corridor linking nesting rookeries with foraging areas as far away as Egypt, Sudan, and Eritrea. For this individual, the connection between a Saudi nesting beach and an Egyptian seagrass meadow was not hypothetical but a documented, round-trip reality.

When the field team found her again on 8 August 2024, 1,077 days after the original tagging, she was nesting on the same beach at Breem Island, within the same island and beach sector where she had first been encountered. The curved carapace length was remeasured at 101.4 centimeters, an increase of just 0.7 centimeters over three years, equivalent to a growth rate of roughly 0.23 centimeters per year. That figure may sound trivially small, but it is exactly what biologists expect from a sexually mature adult female green turtle. Growth in sea turtles is rapid during juvenile stages and slows dramatically after maturity, when energy is diverted from somatic growth into the enormous energetic costs of egg production and long-distance migration between nesting and foraging habitats.

The authors caution that such a small absolute change in carapace length should be interpreted carefully, given the inherent variability in measuring a live, wriggling animal on a dark beach. Even so, the calculated rate falls squarely within the range reported for adult green turtles elsewhere in the Indian Ocean basin, and the turtle’s overall carapace size is consistent with measurements from Red Sea rookeries. The individual appeared healthy at recapture, with no visible injuries, no signs of entanglement, and no residual marks from the satellite transmitter she had carried in 2021. One of her two original flipper tags, RS-033, was missing, a common fate for external tags over multi-year periods, but the other, RS-032, remained intact and undamaged. The team replaced the lost tag with a new one coded RSPSEZ0210, ensuring that future encounters can continue to build her life-history record.

The behavioral story is arguably more significant than the biometric one. Green turtles are famous for natal homing, the tendency of mature females to return to nest on the beaches where they themselves hatched, a behavior supported by genetic studies dating back to the early 1990s. This turtle’s return to the identical beach sector after a three-year absence provides direct, individual-level confirmation of strong site fidelity at Breem Island. Her three-year absence between nesting seasons also fits within the known range of remigration intervals for the species, the period a female spends recharging her energy reserves at foraging grounds before undertaking another breeding season. Such intervals typically span two to four years, and each documented interval adds a scarce data point to a demographic parameter that remains poorly constrained across much of the Red Sea.

That scarcity is precisely why this single recapture matters. As the authors note, marine turtle research in the Red Sea has historically been transient and patchy, with few long-term standardized monitoring programs, leaving persistent gaps in knowledge about remigration intervals, growth rates, and site fidelity for regional populations. Individual recapture records are among the most valuable tools for filling those gaps, because they convert abstract population statistics into concrete life histories. Mark-recapture techniques, including flipper tagging and photo identification, remain the backbone of such efforts, particularly at index nesting beaches where repeated surveys can generate the encounter histories needed to estimate survival, growth, and breeding frequency.

The timing of the research is also tied to a broader transformation of the Saudi coastline. Monitoring efforts in the region have expanded in recent years through conservation initiatives associated with major development projects, including The Red Sea Project, AMAALA, and NEOM. The Saudi Red Sea hosts critical green turtle habitats, including the mainland nesting beach at Ras Baridi and a network of island sites such as Breem, Waqqadi, Ataweel, Al Numann, Shushah, Walah, and Jadir, alongside extensive seagrass feeding grounds. Balancing development with the protection of these habitats requires exactly the kind of baseline demographic data that long-term tagging programs generate, and the Breem Island recapture demonstrates that sustained fieldwork in the area can yield results with direct management value.

There is also a warning embedded in the data. Recent studies have reported declining adult body sizes in parts of the Indian Ocean, a trend that may signal environmental or nutritional stress affecting growth trajectories, potentially linked to the degradation of foraging habitats and climate-driven change. Because adult size reflects decades of accumulated growth and foraging success, shifts in size distributions can serve as an early indicator of population-level trouble. The authors argue that continued monitoring of size distributions across Red Sea green turtle populations is critical to detect such demographic shifts before they become crises, and that findings like this recapture, combined with similar data from other individuals, can inform decisions aimed at protecting key habitats, mitigating habitat destruction, and reducing fisheries interactions.

For now, the turtle tagged as RS-032 has returned to the business of being a green turtle, likely shuttling once more between her Egyptian foraging grounds and her Saudi nesting beach. Her story underscores the quiet power of patient, long-term field biology: a pair of titanium tags, a satellite transmitter, and three years of waiting transformed a single night’s encounter into evidence about growth rates, migration corridors, and the enduring pull of a natal beach. In a region undergoing rapid change, that kind of evidence is the foundation on which the future of Red Sea green turtles will be built, and every subsequent recapture will add another chapter to a life history that researchers, and the public, are only beginning to read.

Subject of Research: Inter-seasonal recapture and site fidelity of a nesting green turtle at Al Wajh Lagoon, Saudi Arabian Red Sea

Article Title: First inter-seasonal recapture of a green turtle (Chelonia mydas) at Al Wajh Lagoon, Saudi Arabian Red Sea

Article References: Barrios-Garrido, H., Al-Attas, O., Al-Ansari, A., Boksmati, T., Al-Johani, M. O., Jabby, K., Wildermann, N. E., Williams, I. D., & Duarte, C. M. (2026). First inter-seasonal recapture of a green turtle (Chelonia mydas) at Al Wajh Lagoon, Saudi Arabian Red Sea. Discover Oceans, 3(1), Article 7. https://doi.org/10.1007/s44289-026-00120-w

Image Credits: AI Generated

DOI: 10.1007/s44289-026-00120-w

Keywords: green turtle, Chelonia mydas, Red Sea, Al Wajh Lagoon, Breem Island, mark-recapture, flipper tagging, site fidelity, remigration interval, satellite tracking, sea turtle conservation, Saudi Arabia

The problem at Breem Island is a product of unfortunate geography. More than 95 percent of the island’s nesting activity occurs along a six-kilometer stretch of coastline on its south and west sides, and while most of the terrain there is sandy and flat, three sections of low rocky sea cliffs sit immediately adjacent to high-density nesting beaches. Female green turtles, hauling themselves ashore at night to lay their clutches, sometimes stray into the areas above these cliffs. On their return journey, they fall over the edge. The consequences are often fatal: turtles have been found dead after falls, or stranded on their backs, unable to right themselves under the weight of their own shells. Between 2018 and 2023, researchers documented nine known mortalities from these cliff falls, a toll that may sound modest until it is placed in the context of the population it affects.

That context is what makes the numbers genuinely alarming. Using recent estimates of nesting activity, and applying standard demographic assumptions—a clutch frequency of 5.9 nests per female per breeding season and an interval of roughly three years between breeding seasons—the research team estimates that only around 135 green sea turtles nest on Breem Island. An average observed mortality rate of 1.5 turtles per year therefore represents approximately one percent of the entire female breeding population dying from cliff falls annually. For a long-lived, slow-reproducing species in which adult survival is the single most important demographic parameter, the sustained removal of even this level of mortality could meaningfully influence population trajectory. Sea turtle populations are shaped by many factors, but every adult female lost represents decades of accumulated reproductive potential, and conservation biologists have long emphasized that protecting adults yields the greatest returns for species of this kind.

The response, launched in 2024 as the Breem Island Cliff Barrier Project, drew inspiration from an unlikely but proven source: the turtle protection fences deployed on Raine Island in Australia, where similar hazard-mitigation strategies have been used to safeguard nesting turtles. The design brief for Breem was demanding. The team wanted an approach requiring limited maintenance, with a natural aesthetic that would not mar the island’s landscape, and crucially one that could be installed without heavy machinery in an ecologically sensitive location. The island also supports significant seabird colonies and other wildlife, meaning any intervention had to minimize noise, disturbance, and transport requirements. The solution they settled on was elegantly low-tech: gabion boxes, lightweight wire structures wrapped in sand-colored fabric, which could be transported to the island empty and then filled in situ with sand by hand.

The technical specifications reveal the care embedded in the design. Each gabion box has a footprint of one meter by one meter and a height of 80 centimeters. When filled with roughly 50 centimeters of sand, each box weighs approximately 800 kilograms—substantial enough to deter a determined adult green turtle, which can weigh well over 100 kilograms itself, yet simple enough to be positioned manually. Critically, the boxes were installed with 30-centimeter gaps between them. These gaps are deliberate: they allow smaller fauna, including seabirds, reptiles, and invertebrates, and potentially even sea turtle hatchlings, to move freely through the barrier line, while still blocking the passage of adult turtles. This attention to bycatch of the non-target kind—ensuring the barrier solves one problem without creating another—reflects a mature conservation engineering philosophy that considers the whole ecosystem rather than a single species.

The geometry of the barriers was equally considered. Rather than running a straight line across the beach, the team deployed two 200-meter-long curved barriers, positioned at the northern and southern edges of one of the main cliff areas surrounded by high-density nesting beaches. The curvature is functional, not decorative: it allows controlled redirection of turtles away from the dangerous area above the cliffs and back toward beaches from which they can safely return to the ocean. Crucially, the alignment was designed so that no main nesting area would be impeded. A turtle encountering the barrier is gently channeled along its curve until it reaches safe ground, rather than being trapped or forced to retrace a long and exhausting crawl. For an animal that may expend enormous energy during the nesting process, this matters.

The results from the first monitored season exceeded expectations. During the 2024 nesting season, which runs from March through November, field assessments recorded 23 successful redirections of green turtles—14 at the southern barrier and 9 at the northern barrier—identified through direct observation or, more commonly, through tracks showing turtles interacting with and being diverted by the structures. Even more telling were the negative results: no turtle tracks were observed in the hazardous area above the managed cliff zone, indicating that the barriers achieved complete effectiveness in preventing access, and no turtle mortalities were recorded within the protected zone across the two nesting seasons since installation. For an intervention costing relatively little and requiring no ongoing active management, the first-year return on investment, measured in turtle lives, is difficult to overstate.

The significance of the Breem barrier system extends well beyond a single island. It represents the first cliff-hazard mitigation project for sea turtles anywhere in the Red Sea, and it offers a template for other rookeries in Saudi Arabia and the wider region where natural topography or anthropogenic structures create hazardous dead-ends for nesting females. The most obvious candidate is Ras Baridi, the region’s most important green turtle nesting site, where sea cliffs have been documented contributing to strandings and falls of nesting females, with several mortalities recorded from this cause both recently and historically. No barrier system has yet been installed there, but the Breem pilot demonstrates that even small, strategically placed barriers can drastically reduce mortality risk. The approach could also prove relevant far beyond the Red Sea, wherever cliffs, seawalls, or other obstacles adjoin turtle nesting beaches—a hazard that researchers have flagged as an emerging concern in the face of sea-level rise and coastal development.

The research team is candid about the limits of the current evidence. A full assessment of the barriers’ impacts on sea turtle populations, on other fauna, and potentially on beach dynamics themselves will only become evident over longer timeframes. Coastal armoring structures are well documented to alter sand transport and beach morphology in some contexts, and introducing any hard structure onto a dynamic coastline warrants continued monitoring. Encouragingly, the gabion design’s permeability and natural appearance were chosen specifically to minimize such risks, but the authors acknowledge that unintended consequences for other species or for sediment movement cannot be ruled out without longer observation. Given the promising first-year results, the team intends to expand protection to the other two Breem cliff areas where mortalities have been recorded, extending the coverage of what has so far proven a remarkably effective solution.

What makes this story resonate beyond the technical details is its demonstration that conservation does not always require heroic, expensive, or technologically sophisticated interventions. Two hundred meters of sand-filled wire boxes, positioned with ecological insight and geometric care, appear to have closed a lethal gap in the life cycle of an isolated turtle population. In a world where marine conservation often grapples with intractable problems—bycatch in industrial fisheries, warming oceans, plastic pollution—the Breem Island project is a reminder that sometimes the right answer is local, specific, and refreshingly simple. For the roughly 135 female green turtles that return to Breem’s beaches year after year, the cliffs that once claimed one of their number annually now stand behind a humble line of sand-colored barriers, and the path from nest to sea is safe once more.

Subject of Research: Cliff-hazard mitigation barriers protecting nesting green sea turtles on Breem Island, Saudi Arabia

Article Title: Innovative barriers reduce risk of injury and mortality for nesting green sea turtles on Breem Island, Saudi Arabia

Article References: Jabby, K., Williams, I. D., Hardenstine, R. S., Barrios-Garrido, H., Al-Ansari, A., & Al-Attas, O. (2026). Innovative barriers reduce risk of injury and mortality for nesting green sea turtles on Breem Island, Saudi Arabia. Discover Oceans, 3(1), Article 14. https://doi.org/10.1007/s44289-026-00130-8

Image Credits: AI Generated

DOI: 10.1007/s44289-026-00130-8

Keywords: green sea turtle, Chelonia mydas, Breem Island, Red Sea, nesting beaches, conservation engineering, gabion barriers, hazard mitigation, Saudi Arabia, sea turtle mortality, hawksbill turtle, coastal management