Understanding Aggregations Sites of Elasmobranchs in selected islands of the Lakshadweep archipelago

Abstract

This Study shows the identification of the aggregation sites of the elasmobranchs, i.e., sharks, rays, and skates, belonging to the Lakshadweep archipelago, emphasising the identification of aggregation places and traditional knowledge regarding related habitats and species. The presence of elasmobranch aggregations is biologically important as it addresses essential life processes like feeding, reproduction, and nursery grounds. Semi-structured interviews were conducted with 120 respondents, including fisherfolks and scuba divers at four selected Islands of Kavaratti, Kadmat, Bitra, and Agatti on traditional ecological knowledge and information about the presence of elasmobranch species and their aggregation sites. Sixteen aggregation sites were reported, nine for rays and eight for sharks. These aggregations occurred most frequently during the post-monsoon season and the early morning hours. The major habitats ecountered with these aggregations were shallow sandy lagoon, coral and rocky reef, sand, and open ocean pelagic zone. The interviews conducted for assessing species composition included a collective 24 species of sharks and 13 species of rays, with dominant encountered species such as the Whale shark, Blacktip Reef Shark and Tawny nurse shark, for rays Spotted eagle ray, Porcupine ray and Oceanic manta ray. 14 species of sharks are aggregating: Whitetip reef shark, Blacktip shark, and Blacktip reef shark are dominant in the aggregation sites. For the ray aggregation site total of 10 species were reported as they formed aggregations from the Porcupine ray, Spotted eagle ray, Cowtail Ray, and Indian Ocean blue-spotted mask ray. Key aggregation sites are such as Cheriyapani, Valiyapani, and Suheli Par, were identified as key elasmobranch aggregation hotspots. Pole and line, hook and line the traditional fishing practices in the islands. The result of the habitat surveys confirmed these findings, showing that lagoon areas are particularly important for the aggregation of rays, whereas coral reefs in Kadmat, Kavaratti, and Bitra host potential shark populations. In Bitra, rays were observed feeding on a locally frequent prey species called "Muchroli," suggesting distinctive trophic interactions. Moreover, drone surveys validated the presence of huge aggregations of rays in pristine reef habitats, such as Cheriyapani, Valiyapani, and submerged banks offshore, including Suheli Par and Perumal Par. These locations are likely to serve as refugia, with the best possible conditions for feeding, resting, and potential nursery grounds, primarily due to minimal human disturbance. This research provides the first comprehensive understanding of the ecological knowledge of sharks and rays, including their species and key habitats. The results highlight the imperative necessity for continuous long-term monitoring, understanding their ecology of specific fisheries management and habitat, to protect these ecologically specialised and at-risk species in the Lakshadweep archipelago.