Conserving an extinct species

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.

  • A dugong around Ritchie's archipelago (Photo: Vardhan Patankar)

  • A seagrass meadow dominated by short-lived species that dugongs clearly prefer

  • A dugong surfacing to breathe (Photo: Vardhan Patankar)

  • A typical meadow with mixed seagrass species (Photo: Vardhan Patankar)

  • Dugong feeding trails (Photo: Vardhan Patankar)

  • Mixed species seagrass meadow (Photo: Vardhan Patankar)

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.

Dugong 203 havelock 20island photo  20vardhan 20patankar

Our studies have been able to individually identify several dugongs in the A&N archipelago (Photo: Vardhan Patankar)

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.

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  • Popular Article
    2015
    Marine Meadows – Following The Feeding Trail Of The Dugong
    Sanctuary Asia, Vol. XXXV No. 1, February 2015.
  • Popular Article
    2015
    A day to celebrate the dugong-a story of their conservation
    Andaman Chronicle, 04, October
  • Journal Article
    2015
    Seagrass Herbivory Levels Sustain Site-Fidelity in a Remnant Dugong PopulationSeagrass Herbivory Levels Sustain Site- Fidelity in a Remnant Dugong Population
    PLoS ONE 10(10): e0141224. doi:10.1371/journal.pone.0141224
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    Seagrass Herbivory Levels Sustain Site-Fidelity in a Remnant Dugong Population

    Herds of dugong, a largely tropical marine megaherbivore, are known to undertake long-dis- tance movements, sequentially overgrazing seagrass meadows in their path. Given their drastic declines in many regions, it is unclear whether at lower densities, their grazing is less intense, reducing their need to travel between meadows. We studied the effect of the feeding behaviour of a small dugong population in the Andaman and Nicobar archipelago, India to understand how small isolated populations graze seagrasses. In the seven years of our observation, all recorded dugongs travelled either solitarily or in pairs, and their use of seagrasses was limited to 8 meadows, some of which were persistently grazed. These meadows were relatively large, contiguous and dominated by short-lived seagrasses spe- cies. Dugongs consumed approximately 15% of meadow primary production, but there was a large variation (3–40% of total meadow production) in consumption patterns between meadows. The impact of herbivory was relatively high, with shoot densities c. 50% higher inside herbivore exclosures than in areas exposed to repeated grazing. Our results indicate that dugongs in the study area repeatedly graze the same meadows probably because the proportion of primary production consumed reduces shoot density to levels that are still above values that can trigger meadow abandonment. This ability of seagrasses to cope per- haps explains the long-term site fidelity shown by individual dugongs in these meadows. The fact that seagrass meadows in the archipelago are able to support dugong foraging requirements allows us to clearly identify locations where this remnant population persists, and where urgent management efforts can be directed.

  • Popular Article
    2014
    Mermaid's second life
    Down to Earth, September issue, http://www.downtoearth.org.in/content/mermaids-second-life
  • Popular Article
    2014
    The Constant Gardner
    Current Conservation, Issue 8.2, http://www.currentconservation.org/?q=articles/feature&n=297
  • Book Chapter
    2013
    Dugongs in Asia. In Sirenian conservation: Issues and strategies in developing countries.
    Ellen M. Hines, Kanjana Adulyanukosol, Sombat Poochaviranon, Phay Somany, Leng Sam Ath, Nick Cox, Keith Symington, Tint Tun, Anouk Ilangakoon, Hans H. de Iongh, Lemnuel V. Aragones, Shaoyong Lu, Xia Jiang, Xin Jing, Elrika D'Souza, Vardhan Patankar, Dipani Sutaria, Bharat Jethva, Parimal Solanki
    Florida: University of Florida Press.

    Ellen Hines. John Reynolds, Lemnuel Aragones, Antonio A. Mignucci- Giannoni, Miriam Marmontel. (Ed.)

  • Newsletter
    2013
    Where have all the dugongs gone? A study on long-term occupancy trends in the Andaman and Nicobar archipelago, India,
    Sirenews, Newsletter of the IUCN Sirenia Specialist Group, Vol. 60.
  • Newsletter
    2013
    Protecting the dugong: Better late than never
    Special bulletin of the 59th Wildlife Week Booklet Department of Environment and Forests, Andaman and Nicobar Administration, September issue.
  • Journal Article
    2013
    Long-Term occupancy trends in a data-poor dugong population in the Andaman and Nicobar Archipelago
    PLoS One. 8(10): e76181

    Prioritizing efforts for conserving rare and threatened species with limited past data and lacking population estimates is predicated on robust assessments of their occupancy rates. This is particularly challenging for elusive, long-lived and wide- ranging marine mammals. In this paper we estimate trends in long-term (over 50 years) occupancy, persistence and extinction of a vulnerable and data-poor dugong (Dugong dugon) population across multiple seagrass meadows in the Andaman and Nicobar archipelago (India). For this we use hierarchical Bayesian dynamic occupancy models accounting for false negatives (detection probability,1), persistence and extinction, to two datasets: a) fragmentary long-term occurrence records from multiple sources (1959–2004, n = 40 locations), and b) systematic detection/non-detection data from current surveys (2010–2012, n = 57). Dugong occupancy across the archipelago declined by 60% (from 0.45 to 0.18) over the last 20 years and present distribution was largely restricted to sheltered bays and channels with seagrass meadows dominated by Halophila and Halodule sp. Dugongs were not found in patchy meadows with low seagrass cover. In general, seagrass habitat availability was not limiting for dugong occupancy, suggesting that anthropogenic factors such as entanglement in gillnets and direct hunting may have led to local extinction of dugongs from locations where extensive seagrass meadows still thrive. Effective management of these remnant dugong populations will require a multi-pronged approach, involving 1) protection of areas where dugongs still persist, 2) monitoring of seagrass habitats that dugongs could recolonize, 3) reducing gillnet use in areas used by dugongs, and 4) engaging with indigenous/settler communities to reduce impacts of hunting.

  • Popular Article
    2012
    Dugongs, mermaids of the sea
    The Hindu in School, 26 September

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