Sea Snakes of the Gulf of Mannar Marine
The Species and their Conservation
The Rufford Small Grants Foundation, UK
Aaron Savio Lobo
Chapter 1. Gulf of Mannar: A marine biodiversity hotspot 6
Chapter 2. Sea snakes of the Gulf of Mannar. A key to their Identification 11
Chapter 3. Trophic ecology of sea snakes in the Gulf of Mannar 27
Chapter 4. A status survey of the dog-faced water snake (Cerberus 36
rynchops) of the islands of the Gulf of Mannar Marine National Park.
Chapter 5. Fisher perception towards sea snakes in the Gulf of Mannar 48
Marine National Park.
Appendix 1. A comparison of scale counts of sea snakes collected from 60
the Gulf of Mannar with descriptions by Malcom Smith (1926)
Appendix 2. The Many-toothed sea snake (Hydrophis caerulescens). 61
A new sea snake species record for the Palk Bay.
Appendix 3. A significant variation in coloration between mainland 63
and island individuals of Cerberus rynchops
Appendix 4. Education and outreach 65
The Tamil Nadu Forest Department – Chief Conservator of Forests, Dr. Sukhdev Thakur for granting me permission to carry out this study (Reference: WL. 5/70173/04/Dated 17.12.2004). Special thanks are due to the ex-Wildlife Warden of the Gulf of Mannar Marine National Park, Mr. V. Naganathan who I have been in constant association with throughout my field work. He has greatly facilitated the educational outreach component of this project in the form of development of posters, booklets and helping me host presentations on the subject. I have also benefited a lot from the discussions and the support I received from Dr. Sudanshu Gupta, Wildlife Warden who later replaced Mr. V. Naganathan.
The Rufford Foundation for funds to carry out this work, without which none of this would have been possible.
Logistic support and assistance throughout this project was all made possible through contacts of the Royal family and once rulers of the Ramanathapuram district (The Sethupathy family). Here I would especially like to thank Mr. Giriraj and Mrs. Banumathi.
Trawler owners – Mr. Suresh Leon (Pamban), Mr. Iqbal Marakyar (Mandapam), Mr. Gunaseharan (Ervady) and L.C. Marine Co. In Rameswaram without whom collection of sea snakes would not have been possible. My field assistants Mr. X. Pally Pritam, Mr. Ryan Meredith, Mr. D. Avinandan and S. Arun Kumar served as excellent companions throughout this project.
Dr. Harold K. Voris, Field Museum of Natural History, Dr. Bivash Pandav, Wildlife Institute; Dr. Sushil K. Dutta, North Orissa University for having faith in my work and supporting this project as referees.
The Bombay Natural History Society for permissions to access their museum collections. For this I am especially grateful to the director Dr. Asad Rahmani. Mr. Varad Giri and Mr. Vithoba Hegde for all assistance provided at this museum.
Finally I would like to thank Solano DaSilva for his useful comments and Edson Dias who helped with formatting this report.
The Gulf of Mannar: A Marine Biodiversity hotspot
The Gulf of Mannar is located along the south-eastern coast of India. It is represented by the portion of the Indian Ocean along the southern coast of India which is partially enclosed to the north and west by the Indian state of Tamil Nadu. It has a 365 km long coastline extending from Rameswaram in the north to Kanyakumari in the south, which constitutes a part of four districts: Ramanathapuram, Tuticorin, Tirunelveli and Kanyakumari of Tamil Nadu. The Gulf of Mannar covers a total area of 10,500 sq. km in the Indian Ocean stretching across towards Sri Lanka.
The Gulf of Mannar Marine Biosphere Reserve (GOMBR) was set up on the 18th of February, 1989 as part of UNESCO’s Man and Biosphere Reserve Programme (MAB), jointly by the Government of India and the state of Tamil Nadu. It is the first biosphere reserve as well as the first marine protected area in South and Southeast Asia (See Box-1). Given the richness of its biological wealth and its threatened status the area was chosen among six others for inclusion in an action program to secure India's protected areas for future generations.
Box. 1 Man and Biosphere Reserve Programme
Man and Biosphere Reserve Programme (MAB) was launched in 1970 and initiated work in 14 Project areas covering different ecosystem types. The MAB governing body consists of 34 Member States elected by UNESCO's biennial General Conference.
The biosphere reserve concept was initially developed in 1974 and was substantially revised in 1995 with the adoption by the UNESCO General Conference of the Statutory Framework and the Seville Strategy for Biosphere Reserves. Today, there are 480 sites in over 100 countries. The World Network of Biosphere Reserves provides context-specific opportunities to combine scientific knowledge and governance modalities to:
Reduce biodiversity loss
Enhance social, economic and cultural conditions for environmental sustainability
Contribute to the pursuit of the Millennium Development Goals, in particular those
pertaining to environmental sustainability
The regions unique location in the sub-tropical region and the fact that it lies in a sheltered zone has allowed it to harbour several, different micro ecosystems. These include coral reefs, rocks, sea weeds, sea grasses, each with its own characteristic community structure and zonations. This is one of the few regions on the Indian mainland where crucial ecosystems - coral reefs, mangroves and sea-grasses occur in close association with each other. As a result of these unique features, the area supports a diverse spectrum of flora and fauna resources, of taxonomic and economic importance. These include 128 species of corals, 641 species of crustaceans, 731 species of molluscs, 441 finfish, five species of sea turtles and several species of Cetaceans (Whales and Dolphins). The Gulf of Mannar, because of the good sea grass patches it supports is also one of the last remaining habitats for the highly elusive and endangered sea cow (Dugong dugon). Mortality due to incidental capture in fishing nets and killing for its meat has resulted in this species becoming extremely rare in the region.
In terms of its biodiversity the Gulf of Mannar is probably the richest marine protected
area on the mainland Indian coastline
Study Area: The Gulf of Mannar Marine National Park
The study was conducted in trawlers that operated in the region of the Gulf of Mannar Marine National Park (GOMNP). The GOMNP forms the core area of the GOMBR and is located between latitude 08°47' to 09°15'N and longitude 78°12' to 79°14'E, i.e. the area from Rameswaram to Tuticorin and covers a total area of 560 sq. km. It received its national park status in 1986. The coastal plain of the GOMNP has been broadly categorized into four geomorphic units: marine, fluvio–marine, Aeolian and biogenic land forms, each of which are further classified into several sub-categories.
Constituting part of the GOMNP are a chain of 21 islands which form part of the Mannar Barrier Reef, which is 140 km long and 25 km wide between Pamban and Tuticorin. The depth beyond the chain of islands ranges from 3.5 to 15 m.
Trawl fishing operations in the Gulf of Mannar (Jayasankar et al. April 2000) The trawling grounds in the Gulf of Mannar lie between 79o and 79o25’ E Long and 8o46’ and 9o10’N Lat, about 2 – 26 km from the coast. The sea bottom is largely muddy or sandy, though some areas have coral structures. Depth of operation ranges from 20 to 42 m.
Trawl fishing takes place round the year in the Gulf of Mannar. During June – September when the sea is rough due to the South west monsoons, trawlers operate during the day. During October to April about half the trawler units engage in night fishing, while the other half go for two nights and one day fishing. A fishing ban is enforced, through the entire state of Tamil Nadu, from 15th April to 1st June every year.
Map of the Gulf of Mannar Marine National Park depicting locations of the trawler bases along the coast.
Jayasankar, P., M. Anand, and J. Anandan. April 2000. Bottom Trawling – A potential threat to the ecology and benthic communities of Gulf of Mannar. Pages 92-94 in A. C. C. Victor, N. Kaliaperumal, D. Kandasami, G. Maheswarudu, I. Rajendran, I. Jagadis, B. Ignatius, S. Kalimuthu, V. Edwin Joseph, and G. K. Rajan, editors. Souvenir 2000, Ramanathapuram, Tamil Nadu.
Outline of this report
The main body of this report is constituted in 4 chapters, viz. chapters 2, 3, and 5.
Chapter 2 provides a pioneer account to the sea snakes of the Gulf of Mannar Marine National Park. It provides a detailed description to each of these species. A key has been provided to aid researchers and park managers for the easy identification of these species.
Chapter 3 is an account of the dietary specialization of the sea snakes found in this region. Several previously unrecorded prey families and species were documented during this study. The chapter also discusses the links between the foraging ecology and the vulnerability of sea snakes to shrimp trawling
Chapter 4 includes results of a survey for amphibious marine snakes (subfamilies: Homalopsinae and Laticaudinae) conducted on the islands of the Gulf of Mannar Marine National Park. Since the dog-faced water snake (Cerberus rynchops) was the only species encountered on some of the islands of the National Park, this chapter provides details of the status, ecology and threats faced by the species on the islands of the Marine National Park.
Chapter 5 is based on interviews and provides an insight of how fishermen handle and deal with venomous species such as sea snakes that are encountered on trawls. Most importantly this chapter underlines how fishermen view marine resources and the role of local knowledge in the management of these ecosystems.
Besides the 4 Chapters which constitute the main body of the report, I have also included 4 appendices which include additional crucial information and outcomes of this project.
Appendix 1 is a table that outlines important scale counts, which are among the most crucial taxonomic characteristics used in snake identification. This table also provides variations (if any) from the original descriptions.
Appendix 2 is a description of Hydrophis caerulescens, which constitutes the first record of this species in the Palk Bay and a geographical range extension of this species in general. Appendix 3 discusses the significant variation in colour between Cerberus rynchops found on the islands of the Gulf of Mannar and those encountered on the mainland. Finally Appendix 4 outlines the outreach in terms of public education that was carried out as part of this project.
The Sea snakes of the Gulf of Mannar
A survey for sea snakes encountered as trawler bycatch, in the Gulf of Mannar yielded nine species. Two additional species Cerberus rynchops and Pelamis platurus were also recorded; the former while surveying the islands of the marine national park and the latter beached ashore. Thus a total of 11 sea snakes were encountered, which represents nearly half (44%) the sea snake fauna documented in the waters of the Indian sub-continent. All these are first records of the sea snakes in the area. Here I present a key using morphological and scale counts and characteristics to aid in the field identification of these species.
25 species of marine snakes belonging to three families and five sub-families have been documented from Indian waters (Das 2003). Of these, 20 are represented in the family Elapidae, of which 18 belong to sub-family Hydrophiinae (True sea snakes) and two belong to sub-family Laticaudinae (sea kraits); four species belong to the sub-family Homalopsinae under family Colubridae, and a single species Acrochordus granulatus is represented in the family Acrochordidae.
Sea snakes are common in coastal waters of India and are often encountered as bycatch in a number of fishing operations. However, most research on sea snakes in India was conducted in the colonial period (pre-1947) and primarily dealt with the taxonomy of this group (Smith 1926). Ironically, this still remains the most comprehensive piece of work on this group so far produced. Post colonial information available in India is based on opportunistic collections made from a few scattered localities along the coast (Ahmed 1975; Murthy 1977; Murthy and Rama Rao 1988; Kalaiarasan and Kanakasabai 1994; Venkateswarlu, Pattanayak et al. 1995).
The paucity of data has led to only 14 of the 25 species being assessed according to IUCN criteria (Molur, Nameer et al. 1998). Nine of these are placed in the Data Deficient Category, three in the Low Risk Category, one (Fordonia leucobalia) in the Vulnerable Category and one (Homalopsis buccata) in the Critically Endangered Category. However, considering that no systematic research was conducted on any of these species, even placement into these categories cannot be totally justified. It is thus clear that research on sea snakes is still in its preliminary phases. The need of the hour would be to get a clear idea of the distribution of the various species along the Indian coastline, before we can take up specific studies or blindly assign a conservation status to the species.
The Management plan of the Gulf of Mannar Marine National Park is an important document, which maintains details of species and habitats and lays out priorities for their conservation. However lack of research or even a basic survey on sea snakes has resulted in them not being included in the species lists of this document. Thus, though sea snakes are among apex predators in a marine ecosystem they lack the legal protection status they deserve.
The Gulf of Mannar is located along the Southeast coast of the country. The region, by virtue of its location and being in a sheltered zone harbours at least three important marine ecosystem types viz. coral reefs, mangroves and sea grasses and is known to support a high diversity of marine life, which probably ranks it among the most productive and bio diverse regions along the mainland coast of India. As a result of its unique biological heritage there has been a large body of marine biological research that has been conducted on several taxa in this area (Nammalwar and Joseph 2002).
The tropical waters of the Gulf of Mannar are located well within the
distributional range of sea snakes (Voris 1977). However for various probable reasons viz. no commercial value, their venomous nature, difficulties in sampling have led to these creatures being under represented in the research conducted in this area. Thus, except for a few anecdotal notes e.g. see. (Mahadevan and Nagappan Nayar 1965) there exist no records or information on the sea snake fauna of this region. Here I provide the first taxonomic list along with detailed descriptions of the species that occur in the region of the Gulf of Mannar Marine National Park, which can also serve as an identification guide for park managers and researchers in this area.
Sea snakes were collected from shrimp trawlers that fish in the Gulf of
Mannar and land their catches on the bases (Pamban, Mandapam, Ervady, Vembar) along the Gulf of Mannar Marine National Park from Dec 2004 – July 2005. Voucher specimens were deposited in the museum collections of the Bombay Natural History Society (BNHS).
In addition to collections made from trawlers, a systematic survey were carried out across 20 islands in the Gulf of Mannar Marine National Park for the amphibious species such as the Homalopsines and Laticaudines. Besides this, opportunistic collections were also made for specimens that were found cast ashore.
Sampling from trawlers, island surveys and casual beach walks yielded a total of 11 species belonging to three families. All these represent new/first records of the sea snakes in this area. Sampling from trawlers resulted in a total of 106 individuals which constituted 9 species belonging to two families Elapidae (sub-family-Hydrophiinae) and Acrochordidae. These were Hydrophis cyanocinctus, Hydrophis (Microcephalophis) gracilis, Hydrophis fasciatus fasciatus, Hydrophis lapemoides, Hydrophis ornatus ornatus, Hydrophis spiralis, Lapemis curtus, Thallasophina viperina belonging to the former and Acrochordus granulatus belonging to the latter. In addition, the Dog-faced water snake (Cerberus rynchops), belonging to family Colubridae (Sub-family:
Homalopsinae) was encountered on at least seven islands of the Gulf of Mannar Marine National Park. Two live individuals of Pelamis platurus (Elapidae, subfamily: Hydrophiinae) were collected opportunistically that were washed ashore; one on the beach behind the Central Marine Fisheries Research Institute, Mandapam Camp and the other at Ervady.
Here I present a key for the field identification of the marine snakes that occur in the Gulf of Mannar Marine National Park, followed by a description of each of these. During this study, I have also observed that some of these sea snake species were encountered as trawler bycatch in the Palk Bay viz. Acrochordus granulatus, Hydrophis cyanocinctus, Hydrophis (Microcephalophis) gracilis, Hydrophis spiralis, Thallasophina viperina. In addition to these another species Hydrophis caerulescens caerulescens was encountered from the Palk Bay off Rameswaram. This species has also been included in the key in the likelihood of it occurring in the Gulf of Mannar. A description of this species has been included in Appendix 2. Cerberus rynchops has not been included in this key as this species was only encountered in shallow areas of islands and was not encountered as trawl bycatch.
A key to the identification of the marine snake species caught in shrimp trawlers in the Gulf of Mannar and Palk Bay
1. Tail laterally flattened into a paddle shaped structure. Body laterally
compressed________________________Hydrophiinae (True sea snakes)
2. Body is of thick girth and cylindrical with a tapering
tail_____________________________________________________Go to 3
3. Scales on the head and body are granular. White rings encircle the body, which are broad on the ventral surface usually tapering dorsally. Ventrals, poorly developed__________________ Acrochordus granulatus
4. Body generally stout and robustly built in proportion to it’s
length__________________________________________________Go to 7
5. Body slender anteriorly, head is small to tiny and not distinct from the neck
________________________________________________________Go to 8
6. Body elongated and of an almost uniform girth throughout. Head is medium to large and distinct from the neck____________________________________________________Go to 9
7a. Presence of dark grey dorsal bars with narrow creamish white interspaces of fixed width and almost equidistant from each other. Body scales overlap_______________________Hydrophis ornatus ornatus
7b. Parietal scales are usually fragmented. Ventrals are difficult to
8a. Head small and elongated, with a long rostral scale projecting over the lower jaw___________________Hydrophis (Microcephalophis) gracilis
8b. Head is small and shiny black, body slender anteriorly, more than 410 ventrals____________________________Hydrophis fasciatus fasciatus
8c. Head small with a blunt, squarish snout_____Hydrophis caerulescens
9a. Interspaces between annuli/bands 2-4 times broader than bands. This character is more pronounced towards the posterior portion of the body________________________________________Hydrophis spiralis
9b. Interspaces between annuli/bands are narrower than or about the same width as the bands_____________________Hydrophis cyanocinctus
9c. Body with blackish grey bands strongly dilated dorsally; tail with 3 to 5 bands and with a black tip. A prominent yellow horseshoe mark is present on the dorsal surface of the head________________________________________Hydrophis lapemoides
10. Head elongated, unlike any other sea snake. Body usually black/ dark. On the dorsal portion and yellow on the ventral portion
11. Head triangular in shape and distinct from the neck. Ventrals are broad anteriorly and narrow posteriorly________Thalassophina viperina
Description of the sea snakes species of the Gulf of Mannar
Hydrophis cyanocinctus (Daudin, 1803) - Annulated sea snake
Voucher specimen numbers - (BNHS 3365,3366,3369)
Morphological characteristics: Head is moderate, body is elongate and not slender anteriorly with a gradual increase in girth posteriorly.
Colour in life: Body is olive/yellow with black annuli. Each annulus is usually broad dorsally, tapers slightly towards the flanks and again broadens ventrally. The black annuli are broader or as broad as the interspaces between them. The dorsal surface of the head in juveniles usually has a yellow horseshoe mark. Juveniles and younger individuals often have a black ventral stripe that runs through the entire length, which usually fades with age. The horseshoe mark on the head may or may not persist and is usually lost with age, the head attaining a uniform olivaceous or yellowish colour
Scale counts/characteristics: 27 to 35 scale rows on the neck, 37 to 4 scale rows around the thickest part of the body. 290 – 390 ventrals, are distinct throughout.
Maxillary teeth behind poison fangs: 5 or 6
Hydrophis spiralis (Shaw, 1802) - Yellow sea snake
Voucher specimen numbers - (BNHS 3363, 3367, 3368)
Morphological characteristics: Very similar to Hydrophis cyanocinctus in form
Colour in life: Head dorsum is usually a golden yellow, occasionally with sporadic faded black speckling. Body is yellow with 41 to 46 narrow black annuli encircling the entire body. There are wide yellow interspaces between the annuli. This character is more pronounced towards the posterior portion of the body. This can be used as one of the key characters to separate this species from H. cyanocinctus. Similar to H. cyanocinctus, the annuli broaden dorsally and again ventrally and are narrow in the flank region.
Scale counts/ characteristics: 25 to 31 scale rows on the neck, 33 to 3 scale rows around the thickest part of the body. 295 – 362 ventrals, are distinct throughout.
Maxillary teeth behind poison fangs – 6 to 7.
Hydrophis ornatus ornatus (Gray, 1842) - Ornate sea snake
Voucher specimen number - (BNHS 3359)
Morphological characteristics: Head is large. Body is robust and not markedly elongate
Colour in life: Head dorsum is olive green to grey. Body pale brown/ olivaceous on the dorsum with dark broad brown dorsal bands. A key character of this species are the narrow creamish-white interspaces between the dorsal bands which are usually of a fixed width, and are almost equidistant from each other. The dark dorsum extends halfway down the flanks where it meets a creamish white venter at a clear line of demarcation.
Scale counts/characteristics: Sexual dimorphism exists in scale counts with females having consistently higher counts than males. The differences are indicated in the table below.