Tracking changes in dugong populations in the Andaman and Nicobar archipelago
From what is known of dugong numbers in the Andaman and Nicobar archipelago, populations here may already be biologically extinct. But dugongs can be remarkably stubborn in the face of these odds. Understanding what enables their persistence will be critical to evolving a strategy to conserve this species.
Tracking an elusive species
As a long-lived, slow moving and slow-breeding marine mammal, dugongs are particularly vulnerable to extinction. They are globally endangered and, in Indian waters, are restricted to a few tiny pockets like the Andaman and Nicobar Islands. They are primarily herbivores and are highly dependent on seagrass meadows in which they graze. In the A&N Islands, where they were once relatively abundant, our studies have shown a clear historical decline. This decline appear to be caused by accidental trapping in gill nets, boat strikes and stranding, poaching by local communities and legally mandated hunting by the indigenous island communities .
Estimating current populations across this island chain is not easy. The species is elusive and generally shy, and the aerial techniques normally used to estimate densities are generally impracticable in these remote island groups. Fortunately, dugongs leave signs of their passing. They graze extensively in seagrass meadows and leave behind distinctive feeding trails. Our studies have shown that a feeding trail is a clear sign that a dugong has visited a meadow within the last 8 to 10 days. By regularly surveying meadows across the archipelago we can get a good sense of where dugongs are active, even without seeing the animal. Together with direct sightings and an informer network geared to inform us whenever an individual is seen, we have been able to build up a clearer picture of the occupancy of dugongs in the islands.
Conserving dugongs and their habitats
Our occupancy studies are showing that dugongs continue to persist across the island group, albeit at very low densities. Their occurrence is strongly linked to the presence of large contiguous seagrass meadows dominated by fast-growing species like Halophila and Halodule. As these meadows get fragmented, dugongs appear to move away from the area. We have been studying how dugongs use these habitats and our results show that, even at low densities, they can exert a strong pressure of herbivory on the meadow and we are now exploring if they can additionally influence the community composition of seagrass ecosystems in the island group.
Conserving dugongs in the light of their current densities is not an easy task. We are working together with the Department of Environment and Forests in the A&N Islands to evolve a suite of strategies to protect what remains of this population. So far, we have developed a strategy with specific protection and management recommendations for 56 seagrass meadows across the Andaman and Nicobar island chain, based on the level of suitability of a meadow for dugong use and the threat present. Our next step will be to help the management execute some of these recommendations.