The headline number, however, conceals a stark concentration of animals in a handful of rivers. The Chambal River alone accounted for 2,097 individuals, or 69.1 percent of all gharials recorded, followed by the Ghaghra River with 463 animals and the Girwa River with 158. At the other extreme, the survey teams found just one gharial in the Kosi, two in the Bagmati, and seven in the Babai, while nine other rivers supported only small remnant groups. Encounter rates told the same story: on the short but dense Girwa River, observers sighted 7.90 individuals per kilometre on average, and the Chambal yielded 5.18 per kilometre, while the main stem of the Ganga and the Kosi registered barely 0.02 individuals per kilometre, effectively empty of the species despite its name being attached to the entire basin.

Methodologically, the study relied on standardised boat-based visual encounter surveys conducted during the post-monsoon winter months, when gharials bask for long periods on exposed sandbanks and detection probability peaks. Crews moved downstream at a constant speed of 8 to 10 kilometres per hour in daylight hours, with two observers scanning banks through binoculars, logging an estimated 2,280 observer-hours across 190 days of fieldwork. Because each river was surveyed only once, the team deliberately reports counts as minimum population size rather than true abundance, a conservative choice that avoids the assumption that every animal present was seen. Body lengths were estimated visually and converted to five size classes, from hatchlings under 0.6 metres to adults exceeding 3 metres, with adult males identifiable by the ghara, the nasal protuberance that gives the species its name.

The size-class data offer clues about which rivers hold genuine breeding populations. Only the Chambal, Gandak, and Ghaghra rivers contained individuals from every size class, with a high proportion of animals larger than 1.8 metres, a pattern consistent with established breeding. Adult males, which make up less than 1 percent of the basin-wide total, were overwhelmingly concentrated in the Chambal, where 80 of the 107 males recorded were sighted. The Ramganga held 14 males, the Gandak six, the Girwa four, and the Ghaghra three; the remaining occupied rivers had none. Rivers lacking adult males cannot sustain reproduction, and their small populations may represent remnants or habitats too degraded for long-term persistence, underscoring the need for targeted nesting surveys and potentially for translocation of animals from more viable populations.

The long-term recovery picture comes from the Chambal, where the team analysed census data spanning 1979 to 2024 and fitted an exponential growth model. The result was a rate of increase of 7 percent per annum over 45 years, but the trajectory splits into two distinct phases. During the intensive grow-and-release era from 1979 to 1993, when captive-reared juveniles were released into protected habitat, the population grew at 15.6 percent per year, one of the fastest documented recoveries for any crocodilian. After 1993, growth slowed to 4.3 percent annually, a deceleration the authors attribute plausibly to stabilisation following the initial augmentation, though density-dependent effects, changing release intensity, and mounting pressures outside protected boundaries remain alternative explanations. Crucially, the researchers warn that this success story cannot be extrapolated to the wider basin, where their river-wise data reveal a markedly uneven and fragile status.

That caution is grounded in the habitat analysis, which used maximum entropy modelling to predict suitability across the entire river network. The team compiled 1,049 gharial occurrence records, spatially thinned to 556 points, and evaluated 168 candidate models combining different feature classes and regularisation multipliers, selecting two top models with area under the curve values of 0.95 and 0.97. Hydrological variables dominated the predictions: water extraction contributed 22 to 24 percent of model gain, followed by channel width and channel depth, together explaining roughly two-thirds of the modelled pattern. Bioclimatic factors such as precipitation of the warmest quarter played a secondary role, while slope, sand mining, and dry-quarter precipitation contributed minimally. When the final map was classified, only 1,320 kilometres, about 10.4 percent of the network, rated as highly suitable, with another 905 kilometres in the moderate class, leaving 10,716 kilometres, or 84.1 percent, in the very low suitability category.

Perhaps the most instructive finding concerns what the model did not emphasise. Widespread anthropogenic pressures such as fishing intensity and sand mining scored low in statistical importance, but the authors are careful to explain why: these threats co-occur almost everywhere in the basin, giving them little spatial contrast for a correlative model to detect, even though their demographic impacts, including entanglement mortality, nest destruction, and loss of basking and nesting sandbanks, can be severe wherever they occur. Field observations confirmed the ubiquity of these pressures. Sand mining was recorded along 100 percent of the surveyed Kosi and 87 percent of the Betwa, water extraction reached 93 percent on the Betwa and 91 percent on the Bagmati, and fishing activity and human presence were the most frequently observed threats across the basin. Statistical silence, the authors argue, is not evidence of harmlessness.

Climate adds a further layer of uncertainty. Overlaying four decades of downscaled temperature and precipitation data from the CHELSA database onto the suitability map, the researchers found measurable warming along 8,330 kilometres of river, about 65 percent of the network, and precipitation change along 7,090 kilometres. Yet the distribution of suitable habitat showed no consistent spatial association with climatic change: several climatically stable rivers such as the Ghaghra and Girwa held extensive suitable stretches, while some segments experiencing substantial warming remained largely unsuitable. One potential consequence deserves particular attention because gharials exhibit temperature-dependent sex determination, meaning incubation temperature dictates whether hatchlings are male or female. Warming trends near nesting sites could skew sex ratios over time in small recovering populations, and the authors recommend nest-temperature logging and periodic sex-ratio assessment at active nesting beaches in the Chambal and Girwa to catch any shift early.

The deeper lesson of the study is that releasing animals alone cannot rebuild a population if the river itself is degraded. Despite the release of more than 9,000 gharials into Ganga Basin rivers over the decades, most rivers still hold fewer than 100 individuals, and the Ken River, despite a 16-kilometre sanctuary, no longer supports gharials at all after releases stopped in 2007. Across the eleven rivers with both release records and current survey data, historical release effort correlated strongly with present-day counts, but the authors emphasise that where releases were paired with genuine habitat protection, as in the Chambal and Girwa, recovery followed; where protection was absent or inconsistent, animals vanished. The Ghaghra’s unexpectedly large population, apparently sustained by downstream dispersal from the augmented Girwa population upstream rather than by local breeding, illustrates how recovery depends on connected, functioning river systems.

For a species that has hovered at the edge of extinction twice in a century, the new assessment offers both reassurance and a warning. The reassurance is that sustained legal protection, habitat defence, and captive rearing demonstrably work, having lifted the Chambal population from near collapse to more than two thousand animals at 7 percent annual growth. The warning is that this stronghold represents most of what remains: outside a few protected reaches, 84 percent of the basin’s river network is now classed as very low suitability, adult males are nearly absent from most rivers, and sand mining, water extraction, and fishing gear continue to degrade and fragment what is left. The authors identify the Ghaghra, Gandak, Yamuna, and Sharda as priority rivers for restoration and targeted supplementation, and they call for integrated basin-scale monitoring to replace the sporadic, site-specific surveys that have historically obscured the true state of the species. Whether the gharial’s comeback becomes a genuine range-wide recovery or remains confined to a few sanctuary stretches will depend, they conclude, on protecting the rivers themselves, not merely the animals that swim in them.

Subject of Research: Population status and habitat suitability of the critically endangered gharial in the Ganga River Basin

Article Title: Recovery of the critically endangered gharial (Gavialis gangeticus) amid escalating anthropogenic pressures in the Ganga River Basin

Article References: Hussain, S. A., Sharma, S. P., Panda, A. K., Usmani, A. A., Das, G. C., Mahar, N., Rawat, A. P., Sarkar, A., Pichaimuthu, G., Ugemuge, S., Ali, S. Z., Barthwal, S., & Badola, R. (2026). Recovery of the critically endangered gharial (Gavialis gangeticus) amid escalating anthropogenic pressures in the Ganga River Basin. Frontiers in Conservation Science, 7, Article 1920905. https://doi.org/10.3389/fcosc.2026.1920905

Image Credits: AI Generated

DOI: 10.3389/fcosc.2026.1920905

Keywords: gharial, Gavialis gangeticus, Ganga River Basin, crocodilian conservation, population survey, habitat suitability modelling, MaxEnt, National Chambal Sanctuary, sand mining, water extraction, critically endangered species, river restoration