Risks associated with the spatial overlap between humpback dolphins and fisheries in Sindhudurg, Maharashtra, India

The Sindhudurg coast in Maharashtra, India, supports diverse fisheries and is a vital habitat for the Indian Ocean humpback dolphin Sousa plumbea, a species found nearshore along the west coast of India. Here, dolphins cause economic losses to fishermen by competing for catch and damaging fishing gear. Dolphins are also affected by entanglement in or ingestion of parts of fishing nets. There is a need for a systematic assessment of the distribution of risks to dolphins and the specific fisheries most impacted by interactions with dolphins. To bridge this information gap, we (1) analysed the behaviour and locations of dolphin groups in the absence and presence of fishing vessels (2012-2015) and (2) mapped the spatial overlap of dolphins and fishing vessels (2014-2015) to determine high-risk areas for dolphins. We observed 175 dolphin groups, of which 75 groups (43%) engaged in foraging behaviours. Dolphins occurred in approximately 50% (164 km2) of the total survey area, and fishing vessels were observed in 100% of the total survey area (333 km2). The proportion of dolphin groups engaged in foraging behaviours was significantly higher when fishing vessels were present compared to when absent. Gillnet (55%) and trawl (32%) accounted for the majority of observed fishing vessels when dolphins were present. Gillnet vessels had a 95% spatial overlap with dolphin habitat, and trawl and purse-seine vessels each had 86%. We identified 8 high-risk areas that were within ~500 m of the coastline, coinciding with high-density dolphin habitat near estuaries. These results have the potential to inform marine mammal conservation and fishery management in Sindhudurg.