Marine capture-fisheries have expanded ten-fold over the past few decades leading to severe decline in fish stocks as well as populations of non-target or ‘bycatch’ species, which comprise ~ 40% of global catch. Large-bodied, slow growing species, like elasmobranchs, cetaceans, and sea turtles, referred to as marine megafauna, which generally occupy higher trophic levels, are perhaps most severely affected by such mortality. At least 160 species of elasmobranchs and 25 species of cetaceans have been recorded from Indian waters, several of which are regularly caught in fisheries. However, information on them is limited to their catch rates with little data on the drivers of their bycatch. Incidental mortality of cetaceans is even more challenging to record since all species are protected by law and bycatch is discarded at sea.  For my research, I propose to understand how the spatial and temporal patterns of fisheries impact marine megafauna in Indian waters, and to what extent may these be explained by ecological and anthropogenic factors. The chapters of my thesis focus on a) Combining fish-landing site surveys with spatial information on multi-gear fisheries to understand bycatch risk of elasmobranchs at two contrasting locations i.e., Malvan and Visakhapatnam on the west and east coast of India, respectively to test whether bycatch patterns can be generalised across environments, b) testing novel methods to combine oceanographic particle tracking with hierarchical modelling to quantify and elucidate the broader drivers of cetacean bycatch using ocean circulation, remote sensing, and stranding data across India; and c) understanding the behaviour of Indian Ocean humpback dolphins around fishing vessels to explore specific mechanisms of bycatch in Goa, potentially using drone based surveys.   For my first chapter, I have sampled more than 1500 fishing vessels across two seasons at both sites. Gear use and diversity are similar across the sites, but species composition and catch-rates differ. For my second chapter, preliminary results using dead cetacean stranding data from Goa suggest that between 2 - 4 small cetaceans may be dying off its coast per 100 km2 per year, of which at least 30% may be due to bycatch in fishing gear. Altogether, the results of my thesis will elaborate on how and why megafauna species are susceptible to bycatch and help develop plans for species conservation and fisheries management.