Resource use and the impacts of fisheries on two sympatric sea snake species on the West Coast of India.

Species interactions are central to community assembly and ecosystem functioning. Sea snakes play an important role as mesopredators and as intermediate links in coastal marine food webs. However, they are impacted by anthropogenic pressures such as fisheries throughout their range. We investigated differences in resource use between two sympatric sea snake species from the west coast of India, Hydrophis curtus and H. schistosus, and described the impacts of fishing on the interactions of these species. We compared habitat use, diet, and isotopic niche width between species to determine resource overlap. We then compared trophic overlap of each species with the fisheries in the region and tested the effect of fishing intensity on their isotopic niche width. We found that H. curtus used deeper habitats than H. schistosus, resulting in increased spatial overlap with fisheries. The two species also had distinct trophic niches and H. curtus prey formed a larger proportion of fishery catch on average than H. schistosus. This greater overlap could make H. curtus more vulnerable to the effects of fisheries. Both species exhibited expansion in short-term and long-term isotopic niche width along a gradient of fishing intensity which may indicate behavioural changes associated with the presence of fisheries. Hydrophis curtus is a trophic generalist, competes with syntopic species and is dominant in most assemblages. However, H. schistosus exhibits higher plasticity in resource use and may have an advantage over H. curtus. Thus, fishing could alter the relative abundance of these mesopredators with cascading effects through coastal food webs.