First
underwater sighting and preliminary behavioural observations of Dugongs (Dugong
dugon) in the wild from Indian waters, Andaman Islands
Elrika D’ souza 1 & Vardhan Patankar 2
1,2Reef Watch Marine
Conservation, Priyanka Bldg.,50 St. Paul’s Road, Bandra (W), Mumbai, Maharshtra
400050, India
Email: 1 elrikad@gmail.com, 2 vardhanpatankar@gmail.com
Date
of online publication 26 January 2009
ISSN 0974-7907
(online) | 0974-7893 (print)
Editor: Kumaran Sathasivam
Manuscript
details:
Ms # o2002
Received 11
June 2008
Final revised
received 09 December 2008
Finally
accepted 25 December 2008
Citation: D’ souza, E. & V. Patankar (2009). First underwater sighting and preliminary
behavioural observations of Dugongs (Dugong dugon) in the wild from
Indian waters, Andaman Islands. Journal of Threatened Taxa 1(1): 49-53.
Copyright: © Elrika D’ souza & Vardhan Patankar
2009. Creative Commons Attribution 3.0 Unported License. JoTT allows
unrestricted use of this article in any medium for non-profit purposes,
reproduction and distribution by providing adequate credit to the authors and
the source of publication.
Author
Details: Elrika D’souza is currently studying ecological
aspects of the Dugong and its habitat of the Andaman and Nicobar islands and is
also co-researching a study on coral reefs of the Nicobar islands. Vardhan Patankar is currently studying
Coral reef recovery in the Nicobar group of Islands and also co-researching a
study on the Coconut Crab and Dugong
Author
Contributions: The first and
second author have jointly contributed to the study and the current paper
Aknowledgements: We
greatly acknowledge support received by HSBC and SWBG Conservation Fund, USA.
We thank the Chief Wildlife Warden, Department of Environment and Forests, Port
Blair for permitting us to carry out the studies, Dr. A.K. Kumaraguru for his
guidance, Nori and Lucan for their inputs and efforts during our field surveys,
Mitali Dutt Kakar, Director, Reef Watch Marine Conservation for her continuous
support and all at Reef Watch for their consolidated efforts.
Abstract: Sighting of Dugongs in Indian waters have become increasingly
rare due to their declining numbers. Further, there have been no reports on underwater observations on
dugongs in the wild from these waters. During our surveys in the Andaman and Nicobar Islands, we sighted three
independent immature sized dugongs. These individuals were sighted at Havelock and Neil Island and Kodiaghat
in South Andaman Island. In this paper, we report dugong sightings, present
preliminary behavioural observations and emphasise the need to initiate
community based conservation along with monitoring of their habitats.
Keywords: Andaman islands, behaviour, Dugongs in Indian waters, sighting
Introduction
Dugongs (Dugong dugon) are large marine mammalian grazers of the
tropical Indo-west-Pacific region where they feed primarily on near-shore sea
grasses (Johnstone & Hudson 1981; Marsh et al. 1982). They are the only extant member of the family
Dugongidae in the order Sirenia. Dugongs are bottom feeders and spend little of
their time at or near the surface but must surface for 1 to 2 seconds to
breathe at regular and frequent intervals (Anderson 1981). They have a large body size (Spain &
Heinsohn 1975) and a hindgut fermenting digestive system (Lanyon & Marsh
1995). These features, combined with the
relatively low nutrient and energy content of their aquatic plant food, suggest
that they must spend a high proportion of their time feeding in order to meet
their daily food requirements.
The documented geographical range of the dugong extends over the coastal
waters of some 37 countries ranging from east Africa, through south and
south-east Asia to Australia. This herbivorous mammal, inhabiting the marine environment was once
abundant in many parts of its range but numbers have declined and its area of
occupancy has decreased in recent times due to exploitation and loss of habitat
(Marsh et al. 2001). It is currently listed in the IUCN Red List of Threatened
Species as being vulnerable to extinction throughout its global range (IUCN 2007). It is also listed in
Appendix I of the Convention on International Trade in Endangered species of
Wild Fauna and Flora (CITES), which prohibits all trades in this species or any
products derived from it. In India, dugong has been given the highest level of
legal protection and is listed under Schedule I of the Indian Wildlife Protection
Act, 1972.
Dugongs have been reported from the Gulf of Kutch, off the Saurashtra
coast, the Gulf of Mannar and Palk Bay which are part of the Indian main
continent (Lal Mohan 1963; Lal Mohan 1980; Mani 1960; Silas 1961; Frazier &
Taej Mundkur 1990; Kumaran 2002). These
reports have been based on studies carried out on stranded and incidentally
caught dugongs and the only observations on live dugongs from India have been
made by Jones (1967a,b) on a pair of dugongs in captivity at
Mandapam (Gulf of Mannar). Dugongs have
also been reported to be found in the Andaman and Nicobar Islands (Anon 1909;
Jones 1980; James 1988; Bhaskar & Rao 1992; Rao 1990). It has been declared as the State Animal of
these Islands. The only comprehensive
report on dugongs is by Das and Dey (1999) who estimated the presence of around
40 dugongs based on interviews of fishermen and regular divers that had
encountered or sighted dugongs from the Andaman and Nicobar Islands.
To derive appropriate conservation strategies of any endangered wild
animal, an understanding of its behaviour in the wild is important (Buchholz
2007; Caro 1999). Dugong sightings
around the Andaman and Nicobar islands are rare due to their low numbers (Das
1999) and also because it is difficult to sight and make behavioral
observations on aquatic animals that generally live in turbid water and only
come to the surface briefly to breathe (Chilvers et al. 2004). To date, there have been no reports on dugong
behaviour in the wild from Indian waters and studies on dugong diving and feeding behaviours carried out in Australia
have been based on visual observations from boats or shoreline vantage points
(Anderson & Birtles 1978; Reynolds 1981; Anderson 1982, 1998; Marsh &
Rathbun 1990; Whiting 2002) and through satellite tagging (Chilvers et al.
2004). It is expected that the behaviour
may vary, given the climatic, environmental and geographical differences. In
this context, here we report the first underwater sightings and preliminary
behavioural observations of dugongs in the wild from Indian waters, Andaman
Islands.
Materials and Methods
The Andaman and Nicobar Islands are one of the biodiversity hotspots in
the world (Myers et al. 2000), which are located in the
south-eastern part of the Bay of Bengal, between 06045’-13041’N & 92012’-93057’E. The Andaman group consists of 4 large islands, North, Middle, Baratang
and South Andaman Islands forming a super island of over 5,000 km2 in area, surrounded by archipelagoes and isolated islands (Davidar, 1994). The Nicobar group of islands is separated from the
Andaman group by the 10 degree channel. This
group comprise of about 23 islands.
The study was carried out between February 2007 and March 2008. Surveys were carried out around Interview,
North Reef, Neil, Havelock, Chidiatapu, Burmanalla, Kodiaghat, Kamorta,
Nancowry and Trinket. These areas were
selected based on earlier documented records of seagrass beds, dugong
occurrence and informal discussions with local authorities and islanders. Survey sites
were accessed in local dinghies or from the shore by snorkeling and SCUBA
diving. Information on the extent of seagrass beds and species composition was
gathered. GPS coordinates of sites that
showed dugong feeding trails were recorded and these sites were monitored for
the possibility of sighting dugongs. Upon sighting of the animal, underwater observations were made by
maintaining a 2m distance from the individual. The sighted individual’s size, sex, scars and body parts were observed
and photo-documented. The period of time the animal spent at the surface
(surface time) and the time spent submerged between successive surfacing
(submergence time) were recorded. The
behaviour was classified into five categories, feeding (movement of
muzzles over seagrass resulting in ingestion of food), idling (seemingly
undirected activity on a small area) (Anderson 1981), resting (stillness
with absence of any kind of movement), communicating (emission of sounds
in the form of squeaks and barks) and observer directed behaviour.
Results
Three independent immature sized dugongs were sighted. The first dugong was sighted on the south
eastern side of Havelock Island (11056’-11059’N & 92056’-92059’E) and
behavioural observations were made for 47h. The individual was approximately 2m
long, with distinct scars on its body; an X-mark on its head, a line running
back from the right pectoral, roughly circular marks above the left pectoral
and on the underside of the base of the tail and 2 notches on the tail. It was
observed feeding on seagrass (Halodule sp. and Halophila sp.) at
an average depth of 6 m and at a maximum distance of 100m from the shore. It spent a mean period of 9.4 ± 0.7h, n=15 a
day feeding in an area of 0.1km2. The density of seagrass was sparse and the
lengths of the shoots were less than 100mm. When feeding on these low growing sea grasses, the dugong dug into the
bottom with its muzzle, extracting and consuming leaves, stems and
interconnecting rhizomes. In this process, it reworked the upper 20-30mm of
substrate raising clouds of fine sediment and leaving behind distinct long, serpentine
feeding trails (Image 1). It surfaced at
mean intervals of 231.8 ± 13.5 s, n=22 (submergence time) to breathe at an
angle of 450 exhaling once it reached the surface. The breathing pattern comprised of 2 short
breaths at mean intervals of 31.1 ± 6.0 s, n=22 followed by a longer third
breath. The mean total surface time was 59.2 ± 6.0 s, n=22. This was followed by an arching of the body
and a forward roll which raised the mid-dorsal region and then the tail above
the surface giving a downward thrust. The descent was generally at a steeper angle and on reaching the bottom;
the dugong supported itself on its pectorals without the body actually touching
the sea bed. The pectorals were also
used for locomotion on the bottom.
The second dugong was sighted around Neil Island (11049’-11050’N & 93000’-93°02’E) and behavioural observations were made for 54h. It was approximately 2.5m long, had a
distinct crescent scar on the left side above the pectoral, a notch on the
inner side of the left and right pectoral and the left side of the tail and a
scar running along the lower half of the trunk. It was observed feeding on Halodule sp. and Halophila sp.
at an average depth of 9m, and at a maximum distance of 100m from the shore
during the neap tide. While feeding, it
surfaced at mean intervals of 268.4 ± 14.6 s, n=41 and spent a mean period of
2.9 ±0.8 h, n=36 a day feeding. During
the spring tide it was observed idling and resting at this site (Image 2). While idling, it swam at an average depth of
3m and up-to a distance of 300m from the shore. It moved with the help of its tail and surfaced at mean intervals of
326.1 ± 11.8 s, n=29 and spent a mean period of 4.1 ±0.8 h, n=14 a day idling. While resting, it remained close to the
surface without any movement and closed its eyes. It was observed resting for a mean
period of 1.2 ±0.3 h, n=4. While idlingand resting, it just submerged while moving forward without arching
and rolling. It was observed communicatingin the form of long squeaks. Both
the dugongs sometimes had 1-2 remoras attached posteriorly and ventrally to
their bodies and were always preceded by juvenile pilot fish. The third dugong was sighted at Kodiaghat (11031’49.25’’N & 92043’36.68”E) in south Andaman and was observed
for a brief period of 590 s at a depth of 7m. It was approximately 3m long and it showed observer directed
behaviour. It curiously
approached us and stopped at a distance of 2m from us. It then circled us twice surfacing to breathe
between each circling. It followed the
similar breathing pattern of two short breaths and a third long breath. All three individuals were identified as
males and confirmation of the sex was done by an observation of the genital
parts.
Discussion
The only observations on Dugong behaviour in India have been made by
Jones (1967a). These Dugongs were in
captivity at the Mandapam camp in a tank where the water was barely 1m deep and
therefore freedom of movement was restricted. They could only make horizontal
movements and were unable to assume a vertical position. Also, they had become so tame that they had
started accepting food from the hands of the feeder (Jones 1967a). Therefore, our observations differ from that
of Jones as the observations on the Dugongs were made in their natural habitat
and not within a controlled environment. These observations made on dugongs
from Indian waters were found to be similar to those made in Australian waters
i.e. Dugongs were found to spend a mean time of 4.2 min ±1 s at mean depths of
7.2 ±0.1m (Chilvers et al. 2004). However, since these observations were limited to 3 individuals,
generalisations and conclusive inferences can only be made after studies are
extended to a larger population.
Dugongs are very individualistic in their behaviour and movements (Marsh
& Rathbun 1990; Marsh et al. 2002) and hence understanding the behaviour of
individuals and herds in relation to daily cycles, tidal state, environmental
variables can be taken into consideration for the conservation and management
of the species in its local area of occupancy. Another significant observation
was that the individuals exhibited a non-aggressive and exploratory behaviour
which could render them vulnerable to hunting. Therefore we recommend local community-based conservation initiative
programmes along with regular monitoring of Dugong habitats. Low-cost studies
such as this can reveal important information on the unexplored aspects of the
behavioural patterns of the dugong that would be important for formulating
conservation strategies in developing countries like India where Dugong
populations are relatively small.
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