BIOLOGICAL STUDIES ON SEA TURTLES ON THE COAST OF ORISSA
KARTIK SHANKER1, BASUDEV TRIPATHY2 AND BIVASH PANDAV2
1-Ashoka Trust for Research in Ecology and the Environment (ATREE)
659, 5th A Main Road, Hebbal, Bangalore 560024. India
2- Wildlife Institute of India
PO Box 18, Chandrabani, Dehradun 248001. India
Several turtle biologists have studied the olive ridley turtle in Orissa over the last decade and have developed strategies towards turtle conservation. Summarised below are some relevant findings of these studies:
- An increase in mortality was documented from a few thousands in the early 1990s to more than 10,000 per year by the mid 1990s (Pandav, 2000). A review of data suggested that this population may be on the verge of a decline, based on evidence from the failure of arribadas in recent years, a decline in adult sizes and high fishery related mortality (Shanker et al., 2004a).
- Nearshore surveys have shown that sea turtles occur in discrete areas which have been named as ‘reproductive patches’. These reproductive patches have been located off the coasts of Gahirmatha (Pandav, 2000; Ram, 2000) and Rushikulya (Tripathy, 2004), and are expected to occur in the offshore waters of other mass nesting beaches such as Devi River mouth. The patches are about 50 – 75 km2 in size, and extend to a distance of about 5 – 6 km offshore.
- The Wildlife Institute of India tagged 10,000 nesting turtles and 1600 mating pairs in offshore waters from 1995 – 1999. Results showed that olive ridley turtles migrate between mass nesting beaches (Pandav, 2000). Tagged turtles were recovered from southern Tamil Nadu and Sri Lanka, indicating that at least some of the olive ridleys that nest in Orissa migrate to these areas.
- In satellite telemetry studies conducted in 2001, 3 of 4 turtles remained in the offshore waters of Orissa between April and July, 2001, moving within 50 and 200 km of the coast. A fourth turtle migrated to the coast of Sri Lanka in August 2001.
- Genetic studies confirmed the results of tagging and showed that there is no genetic difference between nesting populations in each of the mass nesting beaches. More significantly, the results revealed the distinctiveness of the population on the east coast of India, and suggested that they may be ancestral to populations in the Atlantic and Pacific oceans (Shanker et al., 2004b).
- Satellite imagery studies suggest that the failure of mass nesting at Gahirmatha in 1997 and 1998 is due to natural causes such as erosion and reduction in the nesting habitat due to the impacts of successive cyclones (Prusty et al., 2000).
- There should be more effort to identify and monitor reproductive patches. Identification and protection of these reproductive patches from trawling and other harmful fishing practices will significantly reduce turtle mortality.
- Protection of the reproductive patches (rather than the entire marine sanctuary) is a more effective and efficient way of utilising the limited manpower resources of the state, and can involve local fishing communities.
- Monitoring of turtle nesting and mortality should also be carried out by independent agencies to evaluate success of management measures.
- While reducing current mortality, turtle conservation strategies should be effective in the long term.
- The nesting habitat of sea turtles must be protected; adverse impacts of Casuarina plantations and beach lighting need to be mitigated.
- Rigorous assessments of various developmental activities on coastal and offshore habitats of olive ridley turtles are required
- Satellite telemetry studies will provide important information about migration and offshore distributions of turtles during breeding and non-breeding seasons.
Pandav, B. 2000. Conservation & management of olive ridley sea turtles on the Orissa coast. PhD thesis. Utkal University, Bhubaneswar, India
Pandav, B. & B.C. Choudhury. 2000. Conservation & management of olive ridley sea turtle (Lepidochelys olivacea) in Orissa. Final Report. Wildlife Institute of India, Dehradun
Prusty, B.G., R.K. Sahoo & S.D. Mehta. 2000. Natural causes lead to mass exodus of olive ridley turtles from Ekakulanasi, Orissa, India: a need for identification of alternate sites. In: Sea Turtles of the Indo-Pacific: Research, Conservation and Management (eds. N. Pilcher & G. Ismail) pp. 189-197. ASEAN Academic Press, London, UK.
Ram, K. 2000. Behavioural ecology of the olive ridley sea turtle Lepidochelys olivacea (Eschscholtz, 1827) during the breeding period. M. Sc. Dissertation, Salim Ali School of Ecology, Pondicherry University, Pondicherry, India.
Shanker, K., B. Pandav & B.C. Choudhury. 2004a. An assessment of the olive ridley turtles (Lepidochelys olivacea) nesting population in Orissa, India. Biological Conservation 115: 149 – 160.
Shanker, K., J. Rama Devi, B.C. Choudhury, L. Singh & R.K. Aggarwal. 2004b. Phylogeography of olive ridley turtles (Lepidochelys olivacea) on the east coast of India: implications for conservation theory. Molecular Ecology 13: 1899-1909.
Tripathy, B. 2004. A study of the offshore distribution of olive ridley turtles (Lepidochelys olivacea) in the coastal waters of Rushikulya rookery along the Orissa coast, India. Wildlife Conservation Society – India Program Small Grant, Centre For Wildlife Studies, Bangalore, India.