Anthropogenic restocking of gharial individuals prevents genetic isolation of gharial population in Girwa River, India by geographic barriers imposed by a barrage (original) (raw)
Related papers
The Gharial Ecology Project, also known as the Gharial Telemetry Project, was initiated in June 2008 to investigate the circumstances of the 2007-08 mass die-off of gharials in the 2- 4m size class, totaling 110+ individuals in the lower Chambal River. To date, 20 radiotagged gharials have been tracked successfully throughout the annual seasonal cycle, monsoon and dry periods, for an average of 2+ years per animal, since June 2008 through May 2013. Individual gharials show different patterns of seasonal movement and residency, primarily dependent on size/age. Adult females move as far as 80-120 km each seasonal cycle to join dry season basking-breeding aggregations (>60 adults), and to locate suitable nesting areas. In contrast, sub-adult gharials exhibit restricted movements, typically 10-30 km seasonally, and occupy seasonal residencies only 5-15 km in extent. Some sedentary sub-adults showed virtually no movements, either upstream or downstream. Gharial feed primarily during the monsoonal months of June through September, and bask daily for long periods during the winter months of November through February. Large basking aggregations form in December and January. Mixed basking groups of all age/size classes shift to primarily groups of large sub-adults and adults by mid-February when courting and mating commence. Nesting follows in late March/early April when smaller groups of reproductive females assemble near sandbanks adjacent to deep water. Yearlings (9 months old) from the previous years’ hatch often remain close to the dominant male, rather than nesting females, and the male responds to nearby yearlings with specific displays. Colonial nesting sites are located in areas of minimal disturbance, but locations shift from year to year, depending on local restructuring of the nesting sites. Females open the nests, but do not transport the young to water. Adult females and a singular dominant male remain with hatchlings for 1-2 months, attend the young, and guard them against potential predaors. Large male gharials, with well-developed and prominent gharas, remain individually associated with large groups of young (200-1000+). Large crèches remain together, and young have been observed feeding regularly on small fish. These results are directly relevant to conservation and management. First, the long distance movements of adult reproductive females, and likely adult males responsible for breeding, indicate that an open, dynamic, free-flowing river is critical. Second, illegal fishing, sand removal, and/or riverside cultivation anywhere along the river constitutes disturbance to which wide-ranging gharials are exposed, consequently would have adverse effects on their well-being and survival. Third, the detailed behavioral observations of social and reproductive activities indicate that the gharial population inhabiting the lower Chambal is healthy and thriving, and that annual recruitment is high. Fourth, egg removal to ex situ artificial incubation facilities, and the subsequent captive rearing of young (=head starting) is not necessary for the Chambal population presently, and should be discouraged/prohibited. Fifth, any reintroduction or translocation schemes to move gharials into new habitats should take into account the proclivity for sub-adult gharials to move 10-20+ km, and for adults to move 80-100+km. Lastly, this study sheds new light on the mass die-off of 2007-08. The event was specific to gharials, rapid in its effects and restricted to 12 weeks (from early December through February), and very local in its geographic extent, extending from 12 km above the Yamuna-Chambal confluence in the lower Chambal River to 75 km upriver.
The freshwater Gharial (Gavialis gangeticus) is protected under National and International conservation laws as a critical endangered species. In India, the species is endemic to the Ganges and the Brahmaputra river systems and the populations are purported to have declined drastically due to human activities causing habitat loss. We have studied the habitat use pattern of Gharial from 2006 to 2008. The study was carried out in the Chambal River covering a stretch of 395 km i.e. between Pali to Chakarnagar, in the state of Madhya Pradesh. Sampling strategy consisted of boat transects followed by direct sighting method and data was collected at every 5 km. Gharial habitats was observed 265 km out of 395 km area surveys. Gharial was sighted 51 sites out of 395 km. Habitat preferences of Gharials are attributed to deep pools and steep sand banks for nesting and basking. Conservation implications have been discussed in the light of the results indicating the suitable habitat pattern for the Gharial species in the particular River stretch.
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 (
Scientific Reports, 2021
The gharial (Gavialis gangeticus) is a critically endangered crocodylian, endemic to the Indian subcontinent. The species has experienced severe population decline during the twentieth century owing to habitat loss, poaching, and mortalities in passive fishing. Its extant populations have largely recovered through translocation programmes initiated in 1975. Understanding the genetic status of these populations is crucial for evaluating the effectiveness of the ongoing conservation efforts. This study assessed the genetic diversity, population structure, and evidence of genetic bottlenecks of the two managed populations inhabiting the Chambal and Girwa Rivers, which hold nearly 80% of the global gharial populations. We used seven polymorphic nuclear microsatellite loci and a 520 bp partial fragment of the mitochondrial control region (CR). The overall mean allelic richness (Ar) was 2.80 ± 0.40, and the observed (Ho) and expected (He) heterozygosities were 0.40 ± 0.05 and 0.39 ± 0.05,...
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.
Plos One, 2014
The maintenance of both spatial and genetic connectivity is paramount to the long-term persistence of small, isolated populations living in environments with extreme climates. We aim to identify the distribution of genetic diversity and assess population sub-structuring and dispersal across dwarfed desert populations of Crocodylus suchus, which occur in isolated groups, usually less than five individuals, along the mountains of Mauritania (West Africa). We used both invasive and noninvasive sampling methods and a combination of mitochondrial DNA (12 S and ND4) and microsatellite markers (32 loci and a subset of 12 loci). Our results showed high genetic differentiation and geographic structure in Mauritanian populations of C. suchus. We identified a metapopulation system acting within four river sub-basins (high gene flow and absence of genetic structure) and considerable genetic differentiation between sub-basins (F ST range: 0.12-0.24) with rare dispersal events. Effective population sizes tend to be low within sub-basins while genetic diversity is maintained. Our study suggests that hydrographic networks (temporal connections along seasonal rivers during rainy periods) allow C. suchus to disperse and maintain metapopulation dynamics within sub-basins, which attenuate the loss of genetic diversity and the risk of extinction. We highlight the need of hydrographic conservation to protect vulnerable crocodiles isolated in small water bodies. We propose C. suchus as an umbrella species in Mauritania based on ecological affinities shared with other waterdependent species in desert environments.
PLOS ONE, 2017
The Siamese crocodile (Crocodylus siamensis) and Saltwater crocodile (C. porosus) are two of the most endangered animals in Thailand. Their numbers have been reduced severely by hunting and habitat fragmentation. A reintroduction plan involving captive-bred populations that are used commercially is important and necessary as a conservation strategy to aid in the recovery of wild populations. Here, the genetic diversity and population structure of 69 individual crocodiles, mostly members of captive populations, were analyzed using both mitochondrial D-loop DNA and microsatellite markers. The overall haplotype diversity was 0.924-0.971 and the mean expected heterozygosity across 22 microsatellite loci was 0.578-0.701 for the two species. This agreed with the star-like shaped topology of the haplotype network, which suggests a high level of genetic diversity. The mean ratio of the number of alleles to the allelic range (M ratio) for the populations of both species was considerably lower than the threshold of 0.68, which was interpreted as indicative of a historical genetic bottleneck. Microsatellite markers provided evidence of introgression for three individual crocodiles, which suggest that hybridization might have occurred between C. siamensis and C. porosus. D-loop sequence analysis detected bi-directional hybridization between male and female individuals of the parent species. Therefore, identification of genetically non-hybrid and hybrid individuals is important for long-term conservation management. Relatedness values were low within the captive populations, which supported