M Sc Dissertation(WII)
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Item Assessing Ghost crab distribution, abundance and habitat use along the Coromandel Coast, Tamil Nadu(Wildlife Institute of India, Dehradun, 2025) Keerthi V; Gopi, G.V.Sandy beach ecosystems around the world are facing numerous threats and tremendous pressure due to ever increasing human population. One such threat, relevant to the Indian coastline, is the large scale plantations of shelterbelts of the exotic pine, Casuarina equisetifolia, which alters beach geomorphology. The effects of such plantations on permanent shore-dwelling organisms are poorly studied. Hence Ocypode crabs, the most conspicuous macro-invertebrate on sandy beaches, has been used as a model taxon to study the effects of different kinds of inland vegetation (Casuarina plantations, Mangrove plantations, native dune vegetation) on beach geomorphology and consequently, shore dwelling ghost crabs. The present study aims to - (1) Assess the density, distribution and demography of ghost crabs across treatments (2) Understand variations in habitat use and burrow architecture across treatments (3) Understand the effects of inland vegetation on beach geomorphology 2. A total of 24 transects, temporally replicated thrice each month between January 2025 - April 2025, were walked to estimate densities of ghost crabs using burrow counts as a proxy. 87 burrows across the treatments were cast using a mixture of Plaster of Paris and water and traits such as depth, diameter, shape and branching patterns were studied. Coast characteristics like slope, compactness, beach width, moisture and temperature were recorded at each study site. 3. Mean burrow densities and across shore distribution of Ocypode ceratophthalmus differed across the treatment types, with lowest densities in beaches adjacent to Casuarina plantations. This however wasn't statistically significant. The burrow structures also differed in complexity across treatments with the major drivers for this 7 difference being the size of the crab and the type of inland vegetation. Environmental variables were not found to have significant effects on burrow architecture. 4. The results indicate that the type of inland vegetation affects the population of ghost crabs through changes in beach geomorphology. Ghost crabs were also found to modify the structure of their burrows with changes in the habitat quality and environmental conditions, which gives insights into their adaptive capacities. The study, thus raises questions on the effects of certain management interventions, like the planting of shelterbelts on habitat quality and on the ecology of the species dwelling in the said habitats.Item Estimating Abundance, Habitat Use, and Acoustic Characteristics of Irrawaddy Dolphins (Orcaella brevirostris) in Chilika Lagoon(Wildlife Institute of India, Dehradun, 2025) Sakshi; Kolipakam, Vishnupriya; Gopi, G.V.This study provides a comprehensive assessment of the Endangered Irrawaddy dolphin (Orcaella brevirostris) in Chilika Lagoon, India, through an integrated approach combining visual and acoustic surveys, environmental modelling, and prey availability analysis. Visual line-transect surveys and passive acoustic monitoring (using FPODs) were used to estimate dolphin abundance and explore patterns of habitat use. Dive-time observations revealed that calves and non-calves differ in their diving behavior, with non-calves exhibiting longer and more variable dive durations. Mark-recapture analysis produced corrected abundance estimates ranging from 24 to 32 individuals, with variation influenced by observer mismatches and brief surfacing events. To assess prey availability, catch per unit effort (CPUE) surveys were conducted at 22 sites in collaboration with local fishers. The highest CPUE values were recorded in the high salinity area (Outer channel) and low salinity area (Northern sector), indicating these areas may offer better foraging opportunities. Prey community sampling across 11 sites revealed spatial differences in species richness and evenness, with some locations dominated by a few taxa and others exhibiting high diversity. Richness estimators suggested that the true species count exceeds what was observed, indicating under-sampling in certain areas. Environmental modelling using a negative binomial generalized linear model showed that salinity had a significant negative effect on dolphin acoustic detections, while dissolved oxygen and depth were positively associated but not statistically significant. The frequency ranged from 20 kHz to 200kHz with a median frequency of 98kHz. The interclick interval ranged from 850 millisecond to 1010865 milliseconds with a median of 23605 millisecond. The histogram for ICI displayed a positively skewed distribution, consistent with irregular click trains interspersed with longer pauses. The findings highlight the importance of salinity and prey availability in shaping dolphin distribution in Chilika Lagoon. The results support targeted conservation actions such as regulating freshwater inflow, protecting productive foraging zones, and expanding acoustic monitoring efforts to improve long-term management of this vulnerable population.Item Seasonal Habitat use of and Resource Partitioning between Two Sympatric Crocodilian Populations (Gavialis gangeticus and Crocodylus palustris) in Katerniaghat Wildlife Sanctuary, I(Wildlife Institute of India, Dehradun, 2011) Choudhary, Shikha; Choudhury, B.C.; Gopi, G.V.Gharial (Gavialis gangeticus) and Mugger (Crocodylus palustris) are sympatric in their distribution range in some of the Northern River system of Indian sub-continent. Katerniaghat Wildlife sanctuary along Indo-Nepal border in Uttar Pradesh harbours the second largest breeding population of critically endangered Gharial, after National Chambal Sanctuary. Several studies have been carried out on the ecological aspects of Gharial and Mugger separately but very few studies exist on the sympatric populations and the mechanisms favouring the coexistence of the species. This study has tried to fill this gap by investigating how the resources are shared (Basking sites and Nesting sites) and what are the key requirements that lead to the selection of a particular basking and nesting site. Temporal separation across species and size classes and preference for nearest neighbor has been established. Relative abundance in terms of encounter rate across season, river segments and a gradient of disturbances were studied. Other aspects that have been looked into detail in this study are the impact of tourism and illegal fishing on the flight distance of Gharial and Mugger. Data were collected from December 2010 to May 2011, covering two seasons (late winter and early summer). Entire study was carried out using a non-mechanised boat. Habitat parameters for every sighted basking crocodile were recorded for habitat use and for determining the habitat availability variables at every 100 meters on both banks and on islands were recorded. Nests were located by following the spoor marks of crocodiles. Gharial and Mugger were divided into three size classes (SCI - 3m). Once in a month day survey was carried out to estimate the relative abundance and on every alternate Monday temperature and number of basking individual were recorded at every hour from 0600 to 1800 hrs from a watch tower. Flight distance of crocodiles was recorded from a non-mechanised boat and a mechanised boat by accompanying the tourists. Relative abundance as mean encounter rate (#/20km) was maximum for Gharial juveniles followed by Gharial adult. Mugger juvenile had lowest mean encounter rate (#/20km). Encounter rate was not uniform for the river and it varies across season also. Maximum sightings took place in river segments with sand bars irrespective of moderate to high disturbance. With increase in mean ambient temperature encounter rate declined. Basking sites were selected during summer by Gharial based on depth gradient, current land usage, island, distance to water, slope, platform height and soil moisture while selection of basking site by mugger was based on current land usage, distance to water and depth gradient. In winter, Gharial selected sites based on slope, platform height, soil moisture, current land usage, distance to water and place while Mugger looked for current land usage, distance to water, islands and banks. In winter, there was no temporal segregation between different size classes of Gharial and Mugger while in summer there was a temporal segregation between and within size classes 0f Gharial and Mugger. Choice of slope, height, soil moisture, places and substrata for basking sites were different for Gharial and Mugger. Gharial preferred very gentle slope while Mugger preferred a slight slope. Gharials do not prefer elevated basking platforms whereas Mugger was found basking on elevated platform. GhariaI preferred moist areas for basking and Mugger basked even on little dry substrate. Gharial was seen mostly on Islands and Muggers on banks. Among basking substrate Gharial preferred sand & sand+silt, whereas Mugger was found on a variety of substrata. Mugger moved to side streams (Nalla) in summer while Gharial kept on preferring island for basking. For nest sites there is a significant difference in the use of slope, height, distance to water, places and substrate by Gharial and Mugger. Flight distance for crocodiles was more when there was a disturbance from non-mechanised boat than from a mechanised boat. Mechanised boat is mainly used for tourism purpose while non-mechanised boat for illegal fishing by local people. Between species Mugger was more tolerant to human presence than Gharial. Among hatchlings and adults of Gharial, hatchling showed a late response to disturbance while adults used to be the first one to slide in to water. Girwa river of Katerniaghat Wildlife Sanctuary is one of the very few rivers of India where Gharials re breeding in wild. Though the river stretch is about 20 - 21 km only a small stretch of 5-8 km harbours the maximum number of Gharial and Mugger. This small section is used for both basking and nesting and it is very crucial to protect this small stretch in order to save a critically endangered species from the brink of extinction.