Management of Nepalese Rivers to Conserve Ganges River Dolphin

Abstract

The aim of this dissertation is to use evidence-based research to better understand the ecology of the endangered Ganges River dolphins (GRD, Platanista gangetica gangetica) in Nepalese waterways to account for the potential roles that river dolphins play in riverine ecosystems and to guide effective restoration and protection. Previous studies failed to systematically and rigorously capture globally heightened hydro-ecological issues that threaten GRDs, a shortcoming that this thesis addresses. As a large and mobile apex predator in riverine ecosystems whose conservation supports the protection of a wide diversity of species, I first reviewed how evolutionary trap mechanisms—which threaten the ecological structure of the river basin—affect the dynamics and viability of GRD populations in South Asian waterways. Further, to improve the persistence of GRD, I examined ecological preferences and responses of GRD to environmental and anthropogenic stressors by using systematically replicated field-based datasets at finer spatial and wider temporal scales in large river systems (e.g., Sapta Koshi and Karnali) of Nepal. Globally, I detected six potential mechanisms that likely affect the GRD populations discretely or in combination: (1) habitat modification; (2) occurrence of finite and geographically restricted local populations; (3) ratio of effective to estimated population size; (4) increased risk of inbreeding depression in genetically isolated groups; (5) at‐risk behavioral attributes; and (6) direct fisheries–dolphin interactions. The effects of water regulation on native freshwater biodiversity, especially for megafauna like GRD, are extreme and place populations under a greater risk of extinction by isolation and habitat loss. My study reveals that GRD exhibit ecological responses to flow variations that determine habitat quality and availability; variation in flow resulted in substantial response differences across time and space. This suggests that GRD occupy a variety of habitats to support their life histories and maintain viable populations. A decline in suitable habitats coupled with uninformed water regulations likely places GRDs under severe physiological stress during the low-water season (i.e., January–April), suggesting that reduced flow regimes contribute to the process of endangerment and extirpation of highly endemic aquatic mega species as an immediate response. I found that ad hoc or proportional-based flow management is no longer tenable to maintain the integrity and functionality of aquatic ecosystems. My research highlights that quantifying the relationships of GRDs ecological responses to flow variation is crucial for monitoring the effects of water alteration and determining the minimum flow regime needed for balancing human needs and promoting economic advancement while conserving GRD and riverine biodiversity. Furthermore, high fisheries exploitation rates of GRD-preferred prey sizes (>60% of the total catch per effort), especially during the low water season combined with the risks of 48% (CI: 43–52%) increased behavioral change probability among dolphins exposed to fisheries, increasing the risks of social and biological impairment for exposed dolphins. My study reports drivers and consequences of GRD-fisheries interactions, and can be used to mitigate impacts on small cetaceans. I also found considerable overlap in GRD diel activity coefficients across space, season, and time of day, indicating environmental factors marginally regulate diel activity patterns. Instead, GRD consistently exhibited nocturnal activity peaks despite substantial variation in diurnal activity. This indicates a compromising shift in GRD diurnal behavioral activity as a response to human disturbance, especially fishing events. Interestingly, GRD exhibit behavioural variability in response to spatial heterogeneity, adjusting in highly regulated and modified river systems. My research advances our empirical understanding of ecological needs and life history of GRD in relation to space and time, and supports the development of freshwater cetaceans recovery strategies as well as conservation and management of priority habitats in combination with assisting the processes of societal needs. As a top predator of the riverine ecosystem, effective riverine cetacean conservation strategies can directly or indirectly support the restoration of the degraded riverine ecosystem by maintaining their functions and integrity.