Gharials (Gavialis gangeticus) in Bardiya National Park, Nepal: Population, habitat and threats

Abstract

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. Gharial counts in 2017 – 17 from the Babai and one from the Karnali rivers – consisted of 10 adults, five sub‐adults and three juveniles. In 2019, 19 gharials were counted – 18 for the Babai and one for the Karnali – comprising 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. 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. 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. 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.

Gharial (Gavialis gangeticus) conservation in Bardia National Park, Nepal: Assessing population structure and habitat characteristics along the river channel amidst infrastructure development

“…Similarly, our findings are concurrent to the findings of Bashyal et al. (2021) where they recorded 19 individuals (18 Babai, one Karnali). However, Thapa et al.…”

“…Moreover, the high proportion of Gharials with undetermined sex (39%), as observed in our study, raises significant concerns as it limits our ability to comprehend the population dynamics and the reproductive potential of the species. Similar findings were also reported by other studies that recorded a relatively higher number of unidentified sex Gharials (Bashyal et al, 2021;Khadka, 2011;Neupane et al, 2020;Poudyal et al, 2018). Use of genetic markers for sex identification is advisable yet multiple-year survey using current protocol is recommended.…”

“…Total length of the Gharial was estimated by calibrating with natural objects or landscape features using binoculars and was assigned into different age classes as hatchlings (<120 cm), juveniles (120–180 cm), sub‐adults (180–270 cm) and adults (>270 cm) (Neupane et al., 2020; Rajbhandari & Acharya, 2015). Based on preliminary field visit and published literature review (Bashyal et al., 2021; Neupane et al., 2020; Poudyal et al., 2018; Rajbhandari & Acharya, 2015), 10 pre‐defined habitat characteristics were identified as potentially influencing Gharial occurrences; and those selected variables included: elevation, river width, mid‐river depth, bank width, river substrate type, river bank slope, water temperature, presence/absence of anthropogenic disturbance, invasive alien plant species and basking sites (see Table 2 for details).…”

Gharial (Gavialis gangeticus, Gmelin, 1789) abundance in the Rapti River, Chitwan National Park, Nepal

“…Sighted gharials were approached as close as possible, and their size was estimated by visual examination (Bashyal et al, 2021 ; Lang et al, 2018 ; Lang & Kumar, 2016 ). Gharials were classified into various size‐class categories based on their estimated total length (TL; distance from the anterior tip of the snout to the posterior tip of the tail) as hatchlings (≤1 m TL); juveniles (>1–2 m TL), subadults (>2–3 m TL), adult females (3–4 m TL), and adult males (>4 m TL with the presence of Ghara) (Bashyal et al, 2021 ; Lang et al, 2018 ; Lang & Kumar, 2016 ). Adult males were distinguished with the presence of a “Ghara” which is a clear protuberance at the tip of the snout (Lang et al, 2018 ).…”

Anthropogenic restocking of gharial individuals prevents genetic isolation of gharial population in Girwa River, India by geographic barriers imposed by a barrage

“…Girijapuri barrage built on Girwa in 1976 restricted the resident gharial population to a < 20 km river stretch upstream of the barrage 12 . Two smaller gharial populations located at Chisapani gorge in Karnali (in Nepal, upstream) and in Ghaghra (downstream) are now locally extirpated with no signs of breeding 5,13 . This has made the resident gharial population in Girwa (in Katerniaghat Wildlife Sanctuary) insular, with no dispersal or interactions with other gharial populations due to the geographic barrier formed by the Girijapuri barrage.…”