Why is Trawler a source of diplomatic tensions between India and Sri Lanka?

Trawlers are mechanized boats used for commercial fishing. These vessels have fishing nets called ‘trawls’ capable of ‘trawling’ i.e. casting of fishing nets and dragging them through the water to collect fishes. These are used by the Tamil fishermen off the coast of South India. These enable them to exploit the marine resources to a greater extent than the Sri Lankan fishermen who largely rely on traditional fishing methods. This has been a source of conflict between the 2 countries. Recently, the recovery of bodies believed to be that of Indian fishermen in Sri Lanka has triggered protests in Tamil Nadu.