A Comprehensive Report on the Hook-Nosed Sea Snake Enhydrina Schistosa (Daudin, 1803)

REPTILE RAP #18, 30 November 2016 A comprehensive report on the Hook-nosed Sea Snake Enhydrina schistosa (Daudin, 1803) Hatkar Prachi & Chinnasamy Ramesh* Wildlife Institute of India, Post Box # 18, Chandrabani, Dehradun, Uttarakhand 248001, India * [email protected] (corresponding author) Sea snakes (Hydrophiidae) form an important Act, 1972 (Whitaker et al. 2004). According to component of the coastal habitats of the tropical the IUCN red list, this species falls under Least and sub-tropical marine environment (Padate Concerned category. et al. 2009). Sea snakes spend most of their life Hook-nosed or Beaked sea snake (Enhydrina in the ocean but rarely come out to coastal land schistosa) is one of the commonest sea snakes (Damotharan et al. 2010). They are relatively found in India and other South-east Asian countries. abundant in estuaries and lagoons (Heatwole However, little is known about the distribution 1999; Valenta 2010). These poikilothermic scaly (site- specific records), ecology and natural history vertebrates are ovo-viviparous, respiring through of this species. Hence, the purpose of this paper lungs and fast swimmers in the sea but slow on land is (i) To report the further site-specific record of (Sedgwick 1905; Sharma 2003), comprising about this species from Maharashtra. (ii) To review and 86% of living marine reptile species (Damotharan compile the published information on this snake et al. 2010). They are known for one of the deadliest including negative interaction with humans, neurotoxic and myotoxic venom of all snakes and focusing on India’s coastal states and neighbouring valuable skin (O’Shea 2005). Though sea snakes countries to generate baseline information on are very common, detailed information on these E. schistosa for future studies and management. snakes is lacking. All Sea snakes are protected E. schistosa mostly inhabits the sandy or rocky under Schedule IV of the Indian Wildlife Protection bottom of the sea, river mouths, estuaries, coastal Image 1. Hook-nosed sea snake (Enhydrina schistosa) basking on Chivala beach, Maharashtra, India 19 REPTILE RAP #18, 30 November 2016 lagoons, mangroves and mudflats (Whitaker et gender. The snake was observed with a bulging al. 2004; Varadaraju 2009). During the monsoon, stomach indicating either a swallowed prey or a it is found in tidal creeks and other sheltered female bearing a young one. An earlier study on spots (Rasmussen 1998). The body is greyish on this species from Malaysia found that females the dorsal side with fainter darker cross bands are larger and heavier than males but this study on a white belly (Murthy 1986). An adult ranges contradicted the studies on the Goa coast (Lobo et between 85 and 120 Cm (Daniel 2002; Whitaker al. 2004). However, Voris & Jayne (1979) confirmed et al. 2004). Sea snakes are rarely aggressive that there is no sexual dimorphism in this species. or menacing; however E. schistosa is highly Whitaker et al. (2004) reported that the breeding aggressive compared to other sea snakes (Murthy season of this species is between February and 1986). E. schistosa is one of the most common May. Karthikeyan & Balasubramanian (2007) encountered sea snakes during fishing activities. reported that in E. schistosa mating occurs from They prefer shallow coastal water habitats but October to November and the gestation period when the sea is calm, they advance to offshore is from January to August in the Coromondel waters in search of crustaceans and fishes (Sharma coast. Breeding was reported in November 2003).This often causes bites to fishermen during from the coastal areas at Madras (Karthikeyan & fishing activities. Hence, this one species accounts Balasubramanian 2007). However, the breeding for the vast majority of injuries and deaths from season may vary from place to place due to various sea snake bites in their distribution range. environmental factors (Voris & Jayne 1979). Whitaker et al. (2004) reported this species The species is reported to be active both during distributed all along the Indian coastal states; day and night (Whitaker et al. 2004). Sea snakes nevertheless, site specific reports are few. In India, are active predators and always ingest their prey this species has been reported from the west coast head-first (Thurman & Webber 1984; Voris et al. in Bhavnagar, Amreli, Junagadh, Jamnagar district 1978). Karthikeyan & Balasubramanian (2007) of Gujarat, Goa, Maharashtra, Coromandel coast reported that they are active in the night for and from the east coast in Tamil Nadu, Odisha and foraging. Nevertheless, detailed seasonal activity West Bengal (Sharma 2003; Walmiki et al. 2012; pattern of this species is yet to be studied. These Muthukumaran et al. 2015). Adding to the previous snakes feed mainly on Catfishes, Bombay duck, information from Maharashtra we recorded an E. Gobids and Shrimps (Sharma 2003; Ukuwela et al. schistosa on 30th April 2013 at 1043 hrs (Image1) 2013; Jeyabaskaran et al. 2014). E. schistosa bears on Chivala beach of Malvan, Sindhudurg District, 4-9 young each time but as the mortality rate is too Maharashtra (16° 04’ 10.93”N; 73° 27’ 45.65”E). high relatively few young survive to reach the adult Besides, Chivala beach has developed as a stage (Sharma 2003; Daniel 2002). Despite being marine ecotourism spot (Lad 2013) and fishing venomous, estuarine Crocodiles and White bellied practices are still going on. The temperature of sea eagles (Haliaeetus leucogaster) predate on this the Sindhudurg area varies from 16.3 to 33.8 0C snake (Muhamed 2000). Like most of the other with an average rainfall of 3287 mm from June to snakes, the longevity of E. schistosa is not known. September (Paula et al. 2001). The beach is built True sea snakes never voluntarily leave water up with rocks, and Casurina and Ipomia plantations (Heatwole et al. 2012). Nevertheless, sea kraits are dominate the sandy shore. known to come out of water on land to court, rest, The snake length was about 95cm (Image 1), digest their food and bask during their breeding and was basking from 1040 to 1100 hrs at a 150 season (Heatwole et al. 2012). Yellow-lipped sea metres distance from the low tide line and was not krait (Laticauda colubrine) deposits its eggs on daunted by anthropogenic activity. Since sexual shore (Guinea 1994). E. schistosa in Malaysia has dimorphism is not predominant in this species a synchronous peak in gamete production by (Voris & Jayne 1979), we could not determine the both sexes during September (Heatwole & Cogger 20 REPTILE RAP #18, 30 November 2016 1993). The gestation period varies from November (Whitaker et al. 2004). Also, three cases have to March in Malaysia (Voris & Jayne 1979). The been reported from Sri Lanka where the victims young ones reach maturity at the age of three died within three hours (Kularatne et al. 2014). years (Daniel 2002). Since temperature influences However, there is an apprehension that many of all physiological processes in sea snakes (Heatwole the snake bites were not recorded accurately so et al. 2012) we suspect that this snake came on the above mentioned figures might go up. Most land to bask as it helps to increase metabolic rate cases of snake bite have been reported from to accelerate the digestion process or to facilitate Malaya (Daniel 2002). Ecotoxicological studies the growth of eggs (Ramesh 2012). done on two specimens of E. schistosa of Mandovi Cowles (1962) suggested that the Yellow- estuary in Goa detected the high concentration bellied sea snake (Pelamis platurus) may show a of Polycyclic aromatic hydrocarbons (PAHs) and basking behaviour. Brattstrom (1965) classified n-alkanes in the gut, kidney and liver tissues (Mote P. platurus as one of the group of aquatic reptiles et al. 2015). that bask on the surface. This helps to regulate its A recent phylogenetic study shows that E. body temperature behaviourally by alternately schistosa consists of two distinct lineages in Asia basking and diving (Graham et al. 1971). P. platurus and Australia that are not closely related (Ukuwela maintains its body temperature at 2.40C above the et al. 2013). E. schistosa venom has proved to be sea temperature (Bertalo et al. 2005). However, a source of potential antibiotics agent against sea snakes elevate their body temperature slightly human pathogenic diseases (Damotharan et al. above the water temperature by absorbing solar 2015). In India, so far no population ecology studies radiation in water (Dunson & Ehlert 1971; Graham have been conducted on this species. Since this et al. 1971; Graham 1974). Sea snakes can maintain species is common all along the Indian coasts, it a constant body temperature or keep the body would merit further detailed study of this species’ temperature within a preferred range by basking biology and natural history. Most of the incidental (Graham 1974; Bertalo et al. 2005). captures of E. schistosa are reported from Tamil Major threats to sea snake populations are Nadu (Daniel 2002). Excluder devices need to being entangled during trawling operations,. be developed for the easy use of the fisherman and these snakes are exploited for its venom and to prevent sea snakes from getting entangled in skin in many East Asian countries. E. schistosa fishing nets leading to increase in the fish catch and is commonly encountered as a bycatch in the reduction in human causalities as well as mortality trawler, and other fishing activities along the of sea snakes. Goa coast (Lobo et al. 2005). Passive fishing activities are the major threat to E. schistosa in Acknowledgement the Puducherry coastal region (Muthukumaran We thank the Director and Dean of the et al. 2015). Several individuals get trapped in Wildlife Institute of India, Dehradun for their fishing nets and the fisherman kills them before encouragement and support. We also thank taking them out of the net. From 2013 to 2014 Mr.

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