Herd Size Dynamics and Observations on the Natural History of Dugongs (Dugong dugon) in the Andaman Islands, India

Abstract

In the last four decades, dugong (Dugong dugon) aggregations have been rarely reported from the geographically isolated, vast seascape of the Andaman Islands, India. The Indian Ocean tsunami of 2004, hunting, coastal development, and habitat loss are the major causes of this change in the social system of dugongs in the Andaman Islands. Our long-term monitoring study (2017 to 2022) reveals a changing trend in aggregating behaviour of dugongs. In an inclusive, collaborative effort, we engaged multiple stakeholders using two approaches: (1) creating a spatially spread citizen science network targeting sea-faring agencies—the fishers, forest department, SCUBA divers, and defence bodies (Indian Navy and Indian Coast Guard); and (2) conducting standardized questionnaire surveys (UNEP/CMS) with fishers. Our approach yielded reports of 63 herd sightings of dugongs from the Andaman archipelago. The fishers reported 73.01% of the sightings, followed by the defence bodies (20.63%), forest department (3.18%), and SCUBA divers (3.18%). Smaller herds in our study comprised three to six individuals, with a social structure of “adults only” and “adult–calf.” The larger herds of seven to 13 individuals included an “adult–calf” combination with a greater number of adults accompanying two to three calves. More than 95% of these herd occurrences were reported from sheltered, coastal waters with resource concentrations (large seagrass meadows). Further, we present novel dugong occurrence reports from data-deficient regions like the Jarawa Tribal Reserve and the North Sentinel Island, along with dugong occurrences from Little Andaman, where the population was speculated to be locally extinct after the 2004 tsunami. These findings strongly advocate the involvement of multiple stakeholders as a cost-effective approach to monitoring the distribution and population of dugongs in larger seascapes like the Andaman and Nicobar Islands. Moreover, such an approach would be critical for sensitizing the local stakeholders regarding the conservation and management of large marine mammals such as dugongs.