Indian Journal of Geo-Marine Sciences Vol. 45(2), February 2016, pp. 233-238 Beach dynamics and impact of armouring on olive ridley sea turtle (Lepidochelys olivacea) nesting at Gahirmatha rookery of Odisha coast, India Satyaranjan Behera 1, 2 , Basudev Tripathy 3* , K. Sivakumar 2 , B.C. Choudhury 2 1 Odisha Biodiversity Board, Regional Plant Resource Centre Campus, Nayapalli, Bhubaneswar-15 2 Wildlife Institute of India, Dehradun, PO Box 18, Chandrabani, Dehradun – 248 001, India. 3 Zoological Survey of India, Prani Vigyan Bhawan, M-Block, New Alipore, Kolkata-700 053 (India) *[E. mail:tripathyb@gmail.com] Received 28 March 2014; revised 18 September 2014 Gahirmatha arribada beach are most dynamic and eroding at a faster rate over the years from 2008-09 to 2010-11, especially during the turtles breeding seasons. Impact of armouring cement tetrapod on olive ridley sea turtle nesting beach at Gahirmatha rookery of Odisha coast has also been reported in this study. This study documented the area of nesting beach has reduced from 0.07 km 2 to 0.06 km 2 . Due to a constraint of nesting space, turtles were forced to nest in the gap of cement tetrapods adjacent to the arribada beach and get entangled there, resulting into either injury or death. A total of 209 and 24 turtles were reported to be injured and dead due to placement of cement tetrapods in their nesting beach during 2008-09 and 2010-11 respectively. Olive ridley turtles in Odisha are now exposed to many problems other than fishing related casualty and precautionary measures need to be taken by the wildlife and forest authorities to safeguard the Olive ridleys and their nesting habitat at Gahirmatha. [Keywords: Olive ridley, arribada, Wheeler Island, Nesting beach, Armouring, Erosion, Cement Tetrapod, Odisha] Introduction Favourable nesting habitat is critical for sea turtle reproduction and is central to the survival of sea turtle populations 1 . Beach armouring can eliminate nesting habitat, aggravate erosion, obstructnesting turtles, and lethally entrap turtles resulting to death 1 . Coastal armouring structures impede sea turtle reproduction by limiting access to suitable nesting sites i.e. egg laden females cannot reach favourable habitat above the high-tide mark due to barricades and sea walls 2 . The olive ridley turtle (Lepidochelysolivacea) is well known for its synchronous nesting behaviour, also known as arribada in which several hundreds of thousands of female ridleys nest en-masse 3 . Currently the olive ridley sea turtle has been listed is vulnerable by the IUCN Red List 4 and as per CITES it is prohibited for trade of any kind and also is included in the schedule I of Indian Wildlife (Protection) Act (1972) and is legally protected. The congregation of turtles was observed in front of Wheeler Island (arribada beach) prior to mass nesting and it was restricted to 2 km from the shore. Hundreds of aggregated female olive ridleys generally observed in the third breaker zone of the near shore water of the mass nesting beach and stationed themselves prior to the day of arribada 5 . Major nesting aggregations for olive ridleys occur in a few beaches of Costa Rica and Mexico in the east Pacific 6 , and along Odisha coast on the east coast of India 7&8 . There are three arribada beaches viz. Gahirmatha, Devi and Rushikulya located in Odisha coast. The beach of Gahirmatha is part of Bhitarkanika National Park. The mass nesting of olive ridley in Gahirmatha was first reported by H. R. Bustard, a FAO/UNDP consultant during his all India crocodile survey in 1974 7 . Estimate of mass nesting in Gahirmatha from 1974 to 2001 has been extensively reviewed 9 . Arribada at Gahirmatha during March 1999, where maximum nesting was estimated as ~ 180,000 turtles by applying strip transect method 9 . Before 1989, mass nesting occurred on a 10-km mainland beach near the river mouth, which subsequently got fragmented into smaller islands 10 . Now mass nesting takes place on small islands, each less