Sand addition promotes gharial nesting in a regulated river‐reservoir habitat (original) (raw)
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Gharial nesting in a reservoir is limited by reduced river flow and by increased bank vegetation
Scientific Reports 11:4805, 2021
The gharial (Gavialis gangeticus Gmelin) is a fish-eating specialist crocodylian, endemic to south Asia, and critically endangered in its few remaining wild localities. A secondary gharial population resides in riverine-reservoir habitat adjacent to the Nepal border, within the Katerniaghat Wildlife Sanctuary (KWS), and nests along a 10 km riverbank of the Girwa River. A natural channel shift in the mainstream Karnali River (upstream in Nepal) has reduced seasonal flow in the Girwa stretch where gharials nest, coincident with a gradual loss of nest sites, which in turn was related to an overall shift to woody vegetation at these sites. To understand how these changes in riparian vegetation on riverbanks were related to gharial nesting, we sampled vegetation at these sites from 2017 to 2019, and derived an Enhanced Vegetation Index (EVI) from LANDSAT 8 satellite data to quantify riverside vegetation from 1988 through 2019. We found that sampled sites transitioned to woody cover, the number of nesting sites declined, and the number of nests were reduced by > 40%. At these sites, after the channel shift, woody vegetation replaced open sites that predominated prior to the channel shift. Our findings indicate that the lack of open riverbanks and the increase in woody vegetation at potential nesting sites threatens the reproductive success of the KWS gharial population. This population persists today in a regulated river ecosystem, and nests in an altered riparian habitat which appears to be increasingly unsuitable for the continued successful recruitment of breeding adults. This second-ranking, critically endangered remnant population may have incurred an "extinction debt" by living in a reservoir that will lead to its eventual extirpation. Freshwater habitats occupy less than one percent of the Earth's surface, yet a tenth of all known species inhabit these areas, including a third of all vertebrate species 1. Intense human pressures threaten the rich biodiversity in freshwater environments worldwide 2,3 , particularly the megafauna species which are at greater risk of declines and extinctions, than their smaller taxonomic counterparts 4. The main threats include overexploitation, dam construction, habitat degradation, pollution and species invasion 5. For example, dams not only interrupt river channel connectivity, but also have profound effects on riverine landscapes 6,7. The major driver or grand struc-turing factor of river ecosystems is the natural flow regime, pulsating seasonally with floods and droughts 8-10. River studies, firmly grounded in landscape-level perspectives 11,12 , are increasingly focused on dynamic models and management strategies that help predict restoration outcomes 13-16. For river-adapted habitat specialists, threats associated with loss of channel connectivity, altered flow regimes, and water extraction schemes are often direct and immediate and include increased harvest, restricted foraging opportunities, or loss of aquatic habitats. If the resultant impacts of these freshwater infrastructures, such as dams and irrigation canals, remain unaddressed, they can lead to species' reductions, fragmentations, local extirpations (e.g., Indus River dolphins 17), and regional extinctions (e.g., gharial in the Indus 18). Spatially, freshwater megafauna show the largest range contractions, approaching 99%, in the Indomalaya realm, higher than other regions 19. Natural flood events can result in channel shifts altering river discharge dynamics, and ultimately affect species composition, distribution and abundance. A recent example occurred within the Karnali River basin, the third largest riverine system originating in Nepal and flowing into India. In 2010, after monsoon floods, the active OPEN
Nesting of the Critically Endangered gharial Gavialis gangeticus in Bardia National Park, Nepal
Oryx, 2024
The gharial Gavialis gangeticus is a Critically Endangered crocodilian currently known from only disjunct locations in Nepal and India. The protected stretch of the Babai River in Bardia National Park, Nepal, is home to one of the six subpopulations of gharials that have exhibited recent evidence of reproduction. However, there is limited information available on the gharial population in this region. We conducted surveys during the breeding, nesting and hatching seasons of gharials during - to study the gharial population in the Babai River in Bardia National Park. We located one breeding group of gharials in Soth Khola (- individuals) and one in Dhanuse (- individuals), and we observed pre-mating or mating behaviours in all years. We identified potential nesting areas on sand banks of - m in length. During nesting seasons we found abundant signs of nesting only in Dhanuse, including entry and exit trails of female gharials to and from the water and trial nests. In and we did not find any signs of hatching, probably because of flooding. In we recorded two gharial nests, producing c. hatchlings, in Dhanuse. Our findings indicate that the gharial population in the Babai River is probably nesting annually. We recommend various conservation actions for this gharial population.
Herpetology Notes, volume 15: 179-182, 2022
The gharial Gavialis gangeticus (Gmelin, 1789) is a critically endangered crocodile, endemic to the Indian sub-continent (Lang et al., 2019). The global gharial population size has shown an increasing trend in recent years, with the number of adult individuals estimated to be 650 (range 300-900; Lang et al., 2019). However, habitat alteration and fragmentation caused by damming, as well as rising pressures such as illicit sand mining and fishing, remain a risk for the survival of the species in the wild (
Journal of Animal Diversity
The Gharial (Gavialis gangeticus), also known as the gavial or fish-eating crocodile, is a member of the family Gavialidae, is the most threatened of the two species of crocodilians found in Nepal. However, sufficient information on its habitat characteristics influencing population status, distribution, and threats to its existence are lacking. We studied the gharial population in the Narayani River that was carried out in the winter season during December 2019 to April of 2020. During our surveys, a total of 117 gharials were recorded, including an adult male, 56 adult females, 19 sub-adults, 32 immature and nine were unidentified. The gharial census recorded 57 gharials in Sikrauli-Amaltari (Chitwan branch) river section followed by 14 in Sikrauli-Amaltari (Nawalparasi branch), 16 in Amaltari-Baguwan and 30 in the Baguwan-Tribeni River sections. Of 117 individuals, the number of gharials sighted under the direct observation category was 112. The majority of respondents (129 of 140) during our questionnaire, considered gharial as an important species and displayed a favorable attitude towards gharial conservation. This study concludes that the population of gharial in the Narayani River has increased, as the present population is larger than recorded during previous surveys. Finally, regular surveys and monitoring of gharial in the area are recommended to investigate the status of gharial, the prevalence of any threats and disturbance along the habitat of this important species.
Gharials ( Gavialis gangeticus ) in Bardiya National Park, Nepal: Population, habitat and threats
Aquatic Conservation: Marine and Freshwater Ecosystems, 2021
1. The Critically Endangered gharial (Gavialis gangeticus) residing within Bardiya National Park (BNP) in Nepal constitutes the sixth major sub-population of this unique lineage; however, this population is not well studied. A 46 km protected stretch of the Babai River and a 60 km stretch of the Karnali River in and around BNP were surveyed for gharials in early 2017 and in 2019. 2. Gharial counts in 2017-17 from the Babai and one from the Karnali riversconsisted of 10 adults, five sub-adults and three juveniles. In 2019, 19 gharials were counted-18 for the Babai and one for the Karnalicomprising 11 adults, six sub-adults and two juveniles. In the Babai River within BNP, four breeding groups were identified. Gharials in BNP prefer sandy vs. rocky banks for basking and completely avoid sand-grass and clay banks. Habitat preference did not vary with size class. 3. Protected stretches of both rivers inside BNP (76 km) have resident gharial, intact habitats and few human threats. In contrast, the unprotected stretch of the Karnali (30 km) is threatened by boulder quarrying, sand mining and unlicensed fishing, and is avoided by gharials despite the availability of habitat. 4. This study established baseline data, including indices of population size, distribution and habitat preferences, and documented resident gharials that are breeding in the Babai River in BNP. The conservation of this Babai population is crucial for the species' survival in BNP. 5. Based on this study, we recommend the following conservation actions on the Babai stretch: (a) determine hatching success; (b) assess juvenile recruitment; (c) consider supplementation by releasing captives; (d) study riverine features important as baselines; (e) accommodate upstream movements on the protected Babai stretch; and (f) protect the downstream Babai outside the boundary of the BNP.
Aquatic Conservation: Marine and Freshwater Ecosystems, 2009
1. The species diversity of inland waters is among the most threatened of all ecosystems and in many parts of the world it is in continuing and accelerating decline. Such decline could be restrained by acknowledging the scope of target species, so that all relevant stages in their life cycle are considered. 2. The gharial Gavialis gangeticus is a prominent riverine species of the Indus, Ganges, Brahmaputra and Mahanadi river systems that is becoming increasingly rare due to reduction in water flow and available nesting beaches, modification of river morphology and increased mortality in fishing nets. Despite these threats, scientific information on habitat selection by gharial is still inadequate, which hinders conservation measures. 3. This paper presents the population status, basking site selection and water depth preferences of different size-classes of gharial based on a study conducted in the National Chambal Sanctuary, India. 4. Between 1992 and 2007 a 40% decline in the gharial population was observed in the National Chambal Sanctuary. The decline was prominent in the recruitment class (o120 cm), which primarily comes from the nests laid in the wild, and also in sub-adults (4180 to 270 cm) comprising both wild and reintroduced gharial. 5. Along the Chambal River, gharial preferred sandy parts of the river banks and sand bars for basking and showed less preference for rocky river banks and rocky outcrops. Clay river banks were least preferred. 6. Juvenile gharials o120 cm and 120-180 cm preferred water depths 1-3 m and 2-3 m, respectively. Gharial 4180 cm (including sub-adults and adults) preferred water depths 44 m. 7. Increasing demands for sand for development activities, and water abstraction for irrigation and energy generation coupled with mortality in fishing nets, are likely to affect gharial and other aquatic species, and steps need to be taken to maintain the minimum river flow necessary to sustain ecosystem processes.
Conservation and Population Recovery of Gharials (Gavialis gangeticus) in Nepal
Herpetologica, 2017
The remnant populations of Gharials, Gavialis gangeticus, are now confined to the large, deep rivers of northern India and Nepal. In lowland Nepal, the populations are restricted to a few stretches of the Narayani-Rapti and Karnali-Babai river systems. Periodic censuses of the wild populations have been made over the past 12 yr. Here, we present population trends of Gharials in the Narayani, Rapti, and Babai rivers based on these surveys. The results indicate that the combined numbers of adults and subadults have been gradually increasing since 2005, but the numbers of adults are low and female biased, with very few males recorded from all study sites. In 1978, Nepal established a captive breeding center in Chitwan National Park, from which captive-bred animals have been periodically released 4-7 yr after hatching, at which time the animals are about 1.5 m total length. The detection of hatchlings and subadult classes that are smaller than these released animals in the rivers indicates that there is natural recruitment. Therefore, collecting all nests for ex-situ breeding might not be the best strategy until more rigorous field assessments are completed to determine the relative contributions of captive-bred versus natural recruitment. We suggest that more effort should be channeled toward field assessments, including mapping and monitoring habitat availability, habitat management to ensure necessary environmental flows to create sand banks and deep pools, and research to better understand the ecology and behavior of Gharials in Nepal's rivers.
Spatial Ecology of Gavialis gangeticus in the Chambal River, India
CSG 20th Meeting Proceedings. Manaus, Brazil, 2010
Following the die-off of Gavialis gangeticus in the Chambal River during winter 2007-08, ecological and behavioral studies were initiated on the resident population inhabiting a 30km stretch of river, upstream of the affected area. Ten gharial (8 females, 2 males; 2.0 to 3.3m, totl) were monitored via radiotelemetry over 14-22 months, 3-5X weekly (June 2008 thru April 2010). Local trackers recorded >2000 daily locations over the last 14 months, traveling by motorbike/on foot to elevated riversides near known basking areas.