The coconut crab Birgus latro, categorized as Data Deficient on the IUCN Red List (Eldredge, Reference Eldredge1996), is the largest land crab. It occurs on oceanic atolls and islands in the Indo-Pacific region and is reported to grow up to 35 cm in length and weigh up to 5 kg. The species' only dependence on the sea is for releasing eggs, which hatch in contact with seawater; the planktonic larvae then migrate onto land where they develop into long-lived adults (Reese & Kinzie, Reference Reese and Kinzie1968). The successful recruitment of larvae to the adult population is irregular (Schiller et al., Reference Schiller, Fielder, Brown, Obed, Brown and Fielder1991; Schiller, Reference Schiller1992).
In many parts of its range the coconut crab is hunted for consumption. A slow growth rate and long life span combined with high levels of exploitation and habitat degradation make the species susceptible to overexploitation (Fletcher & Amos, Reference Fletcher and Amos1994) and in many countries the crab is virtually extinct (Schiller, Reference Schiller1992). However, the length of the planktonic larval phase of the species, which is 3–4 weeks, could provide sufficient time for dispersal and thus establishment of new populations (Brown & Fielder, Reference Brown and Fielder1991; Lavery et al., Reference Lavery, Craig and Fielder1995). Conservation of the coconut crab would not only benefit the current population but also help in the establishment of new populations.
In India the coconut crab occurs on some islands of the Andaman and Nicobar archipelagoes. In the Andaman Islands the species has been reported from South Sentinel (Alcock, Reference Alcock1905) and Little Andaman Island (M. Chandi, pers. comm.). In the Nicobar Islands the species has been reported from Car Nicobar (Hume, Reference Hume1874), Katchal, Great Nicobar, Little Nicobar, Camorta, Menchal and Cabra Island (Daniel & Premkumar, Reference Daniel and Premkumar1968; Altevogt & Davis, Reference Altevogt and Davis1975; Bhaskar & Rao, Reference Bhaskar and Rao1992). These islands were severely affected by the tsunami of 2004 (Ramachandran et al., Reference Ramachandran, Anitha, Balamurugan, Dharanirajan, Vendhan and Divien2005), with the destruction of coastal habitats and some coastal fauna, including the endemic Nicobar megapode Megapodius nicobariensis (Sivakumar, Reference Sivakumar2004). The tsunami could also have affected the coconut crab as it inhabits narrow stretches of coast adjoining coconut plantations (Sankaran et al., Reference Sankaran, Andrews and Vaughan2005). Although incidental sightings after the tsunami confirmed the continued presence of the coconut crab in the Nicobar Islands (Patankar, Reference Patankar2007; Sivkumar, Reference Sivkumar, Raghunathan and Sivaperuman2010) its status was previously unknown.
The coconut crab is afforded the highest level of legal protection in India, categorized under Schedule-I of the Indian Wildlife Protection Act. However, this categorization was based on secondary data rather than field investigations of the species. Lack of information regarding the population, especially following the 2004 tsunami, and existing practices pertaining to hunting of the species has hampered the conservation of the species. The aim of this study was to assess the distribution of the coconut crab's habitat and local attitudes towards the species to provide recommendations for appropriate management and conservation.
The 2,000 km2 Nicobar Islands lie in the south-east Bay of Bengal in the eastern Indian Ocean. The archipelago comprises 21 large and small islands, of which 12 are inhabited (Fig. 1). To the south lies the Great Nicobar group comprising two islands > 100 km2, nine islets > 5 km2, and a few rocks; 58 km north of the Great Nicobar group is the Nancowry group comprising three islands > 100 km2, two, of 36 and 67 km2, three<17 km2, two small islets and a few rocks. The northernmost islands comprise Batti Malv and Car Nicobar, 88 km north of the Nancowry group. Two indigenous groups of people inhabit the Nicobar Islands, the Shompens and Nicobaris, along with some settlers from the Indian mainland. The islands receive heavy rainfall from the south-west and north-east monsoons. The coastal forests of the islands comprise evergreen rainforests and some areas have been planted with coconut palms.
Fig. 1 The Nicobar Islands, India, indicating the nine forest fragments (A–I) in which we searched for the coconut crab Birgus latro. The rectangle on the inset indicates the location of the Nicobar Islands in the eastern Indian Ocean.
During 2008 we conducted informal discussions with Nicobari communities in 11 villages close to potential crab habitats in Car Nicobar, Camorta, Trinket, Katchal and Little Nicobar islands to investigate the likely habitats of coconut crabs, any taboos and people's perceptions of the conservation of the species. Based on the information received in these discussions we searched all potential coconut crab habitats (coastal forests, and crevices, caves and hollow tree stumps in these forests) on four inhabited (Car Nicobar, Camorta, Trinket and Katchal) and two uninhabited islands (Tillangchong and Menchal) during March–May 2008. The coconut crab is nocturnal (Reyne, Reference Reyne1939; Held, Reference Held1963) and night-time searches could result in individual crabs being counted more than once. We therefore carried out surveys during daylight. In each potential location we inserted a small digital camera inside burrows to confirm the presence of crabs. We recorded the number of hours spent searching in each forest fragment, the approximate area of the fragment, the width of each burrow entrance and its distance to the nearest coconut palm, and made observations of the coconut crab's habitat.
We found that there are social taboos associated with hunting of coconut crabs on the Nicobar Islands. None of the villagers were aware that hunting the crab is illegal and that the species is protected under the Indian Wildlife Protection Act. On Camorta Island it is believed that consumption of the crab could bring bad luck and also cause illness that could lead to death. If an individual falls ill following consumption of a coconut crab members of the family make a wooden replica of the crab and perform rituals at the site where the crab was caught. In two villages on Camorta (Nuot and Payuha), small-scale local consumption of the crab is allowed but hunting of the crab by people from nearby villages is prohibited. On Menchal Island the crab is believed to be protected by the spirit of the island, and hunting and consumption of the crab is prohibited in all the villages of Little Nicobar Island, which is close to Menchal Island. However, the villagers of Pulopanja on Little Nicobar Island hunt the coconut crab for consumption. A few villagers, on all the islands surveyed, had never seen a coconut crab but all were aware of the species. The villagers of Katchal Island hunt the coconut crab. On all islands surveyed hunting of the crab for consumption was widespread among young people, whereas elders followed the social taboos set by the community.
Details of the forest fragments searched and the number of coconut crabs located are given in Table 1. On Katchal and Tillangchong we searched for 6 and 4 hours, respectively, but did not locate any coconut crabs, although villagers indicated that the species is present on these islands. We did not locate the species on Car Nicobar and Trinket and villagers indicated they had not seen the coconut crab after the 2004 tsunami and they believe the species is now extinct on their islands. However, further surveys are required on these two islands to confirm this. We located the crab only on Camorta and Menchal islands. On Camorta we found 17 crabs in a forest fragment of 3.2 km2 during a search effort of 28 hours and on Menchal 14 crabs in a forest fragment of area 2.8 km2 during a search effort of 6 hours. All crabs seen were within 50 m of a coconut palm. We sighted 11 crabs in burrows under fallen trees, four between roots of trees and 13 in rock crevices. Two individuals were observed feeding on coconut kernel and one was observed walking on the sandy shore. The soil inside and at the entrance of burrows was dark brown in colour and rich in organic matter. The entrances were clear of debris and covered with finely shredded coconut coir. The widths of the burrow entrances were 25–45 cm. None of the burrows were found in sandy areas close to the shore.
Table 1 Areas of the nine forest fragments searched (see letters in Fig. 1 for locations), search effort and total number of coconut crabs Birgus latro recorded on the six islands.
On all the islands surveyed social taboos are associated with consumption of the coconut crab. The fact that these taboos are still being followed to some extent indicates there is a level of awareness regarding the crab. Currently the only apparent threat to the coconut crab is, however, from hunting for consumption. The proximity of the coconut crab to coconut palms indicates that coconut plantations are an important habitat for the crab. These plantations are regularly visited by the islanders and, as the signs of crab presence (e.g. coconut husk) are conspicuous, these could render them susceptible to hunting. Although the species is protected by legislation the level of awareness of this legislation is low. Furthermore, the indigenous communities of the Nicobar Islands are exempted from the Wildlife Protection Act under the Andaman and Nicobar Protection of Aboriginal Tribes Regulation, 1956, and are allowed to hunt wildlife for subsistence. Legislation for threatened species can be effective if social conditions encourage self-regulation (Reiser et al., Reference Reiser, Hudson and Roady2005) and the social taboos forbidding hunting of the coconut crab on the Nicobar Islands could, if strengthened, be used to promote the coconut crab as a flagship species for raising environmental awareness. As numerous crabs were sighted on Camorta and Menchal these islands could be suitable for the initiation of conservation efforts.
We recommend that more extensive surveys be carried out in all potential coconut crab habitats on the Andaman and Nicobar archipelagoes and that the Andaman and Nicobar Forest Department conduct detailed studies of the coconut crab in collaboration with research institutions working in the islands. Investigations using molecular techniques and population genetic analyses, to assess variability and gene flow between island populations, are also needed. Such research will not only provide new information on the ecology and biology of the species but also identify source metapopulations and provide empirical and technical support for the species' conservation.
Acknowledgements
The study was supported by the National Geographic Conservation Trust. We thank the Department of Environment and Forests, Port Blair, for permitting us to conduct the study and all at Reef Watch Marine Conservation and the Nature Conservation Foundation. We are grateful to the Nicobari villagers, village heads and our field assistants for support and help during the fieldwork.
Biographical sketches
Vardhan Patankar studies coral reef communities and patterns of marine resource use in the Nicobar Islands. His interests are in understanding community dynamics of marine ecosystems and social issues related to marine biodiversity conservation. Elrika D'souza is studying the interactions between dugongs and seagrass meadows around the Andaman and Nicobar Islands.
