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Beach Dynamics and Impact of Armouring on Olive Ridley Sea Turtle (Lepidochelys Olivacea) Nesting at Gahirmatha Rookery of Odisha Coast, India

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Beach Dynamics and Impact of Armouring on Olive Ridley Sea Turtle (Lepidochelys Olivacea) Nesting at Gahirmatha Rookery of Odisha Coast, India 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 Behera1, 2, Basudev Tripathy3*, K. Sivakumar2, B.C. Choudhury2 1Odisha Biodiversity Board, Regional Plant Resource Centre Campus, Nayapalli, Bhubaneswar-15 2Wildlife Institute of India, Dehradun, PO Box 18, Chandrabani, Dehradun – 248 001, India. 3Zoological Survey of India, Prani Vigyan Bhawan, M-Block, New Alipore, Kolkata-700 053 (India) *[E. mail:[email protected]] 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 km2to 0.06 km2. 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 aggregated female olive ridleys generally for sea turtle reproduction and is central to the observed in the third breaker zone of the near survival of sea turtle populations1. Beach shore water of the mass nesting beach and armouring can eliminate nesting habitat, stationed themselves prior to the day of aggravate erosion, obstructnesting turtles, and arribada5. Major nesting aggregations for olive lethally entrap turtles resulting to death1. ridleys occur in a few beaches of Costa Rica Coastal armouring structures impede sea turtle and Mexico in the east Pacific6, and along reproduction by limiting access to suitable Odisha coast on the east coast of India7&8. nesting sites i.e. egg laden females cannot There are three arribada beaches viz. reach favourable habitat above the high-tide Gahirmatha, Devi and Rushikulya located in mark due to barricades and sea walls2. The Odisha coast. The beach of Gahirmatha is part olive ridley turtle (Lepidochelysolivacea) is of Bhitarkanika National Park. The mass well known for its synchronous nesting nesting of olive ridley in Gahirmatha was first behaviour, also known as arribada in which reported by H. R. Bustard, a FAO/UNDP several hundreds of thousands of female consultant during his all India crocodile survey ridleys nest en-masse3. Currently the olive in 19747. Estimate of mass nesting in ridley sea turtle has been listed is vulnerable Gahirmatha from 1974 to 2001 has been by the IUCN Red List4 and as per CITES it is extensively reviewed9. Arribada at Gahirmatha prohibited for trade of any kind and also is during March 1999, where maximum nesting included in the schedule I of Indian Wildlife was estimated as ~ 180,000 turtles by applying (Protection) Act (1972) and is legally strip transect method9. Before 1989, mass protected. The congregation of turtles was nesting occurred on a 10-km mainland beach observed in front of Wheeler Island (arribada near the river mouth, which subsequently got beach) prior to mass nesting and it was fragmented into smaller islands10. Now mass restricted to 2 km from the shore. Hundreds of nesting takes place on small islands, each less 234 INDIAN J MAR SCI VOL 45, NO.2 FEBRUARY 2016 than one km in length known as Nasi-I and (November to May). To know the exact status Nasi-II Island. Mass nesting of olive ridley of beach, the beach profiling was done every turtles at Gahirmatha takes place between fortnight basis following standard December and March. During a cyclonic storm methodologies11&12. Available nesting beach in 1989, the long sand spit got dissociated of turtle was calculated by above methods. from the mainland and the mass nesting beach was reduced to a 3 km long island, Nasi-I. The Nasi Island is devoid of any vegetation except for sand binders and creepers and is characterised by small sand dunes of 1-2 ft height. Between 1990 and 2000, significant geo- morphological changes occurred at this Nasi-I Island. Over the last ten years (between 2000 and 2010), the Nasi-I Island has moved nearly 5 km northwards and narrowed to less than 100 m at maximum width. The changes of nesting beach morphology have been provided from 1999 to 2011 at Gahirmatha in Fig. 1 Map of Gahirmatha rookery and recent mass the Fig. 2. This island has now moved further nesting locate in south-western side of Wheeler Island. north and connected with the Wheeler Island through a narrow strip of sand spit. Since Beach profiling was done from beginning of 2009, arribadas have been restricted to 900 m November to end of March, which is coincided island beach connecting with south-western with turtle nesting season. The total beach was part of Wheeler Island, where there is a divided into 10 segments to cover entire Defence Research Development Organization nesting beach and each 100m segment wooden (DRDO) establishment (Fig. 1). Wheeler pole was fixed to carryout beach profiling. Island is inhabited only by Defence personals Beach width (b) was measured from the and there are buildings and other landmark (a) perpendicular to the high tide infrastructures built for DRDO purpose. The line. Similarly the beach width was calculated island is exposed to Bay of Bengal to its east in every 100m segments. After that average and on the western side by Dhamra river width was taken and multiplied in total length mouth forms a huge lagoon and therefore, the of the beach. Geo-coordinate of the landmark eastern side is subjected to frequent erosion was recorded in a handheld GPS (Garmin 72, and consequent loss of space for infrastructure Garmin Inc.) for plotting on a toposheet. Data close to high tide line. Therefore, to protect the on the beach availability was collected on a island from wave actions, some portion of the fortnightly basis. The available beach was beach is protected with concrete cement estimated using the formula as suggested by tetrapods. This includes portions of the beach earlier literature12. where arribadas have been occurring for the Width of beach l = a + b last couple of years. This paper deals with Here, b is from the width of beach permanent beach dynamics and impact of armouring on land mark (a).Where, ‘b’ is the calculated nesting habitat of olive ridley turtles at value of beach width difference from earlier Gahirmatha rookery of Odisha coast in India. observation of permanent land mark (a).The average loss of beach width (l) was multiplied Materials and Methods into the total length of the beach to find out the 0 ’ Gahirmatha sea turtle rookery (20 44 N, total area lost (L) because of beach erosion. 0 ’ 87 5 E) is situated in the north east part of Bay Additionally, the beach area which has been of Bengal in Odisha coast of India (Fig. 1). armoured with concrete cement tetrapod was Present work was concentrated on a < 1 km also calculated using the same formula. long beach where mass nesting has been occurring since 2007. The study was carried out for three years between 2008-09, 2009-10 and 2010-11 during turtle breeding season Behera et al.: BEACH DYNAMICS AND IMPACT OF ARMOURING ON OLIVE RIDLEY SEA TURTLE AT 235 GAHIRMATHA ROOKERY Results structures as turtles observed entangled in the gaps in the armoured cement tetrapods (Fig. 3). A total of 209 (mean ± SD = 8.3 ± 3.6) turtles were found to be injured and 24 (mean ± SD = 0.96 ± 1) dead in the tetrapod laid area (Table 1). Fig. 2—Changing of nesting beach profile over the years at Gahirmatha Fig.—3 The placed tetrapod and armoured area near turtleturtle nesting beach threats the biodiversity Similarly, the area with armouring was estimated to be approx. 1.05 km2. However reductionreduction rate is very low, this reduction of the nesting space presumably turtles forced to crawling to areas armoured with concrete Table 1—Number of turtles get injured and found dead in tetrapod laid area during arribada period in three years period of study Year Arribada days Total injure (%) Total dead (%) 2008-09 21st-25th March 64 (30.6) 5 (20.8) 2009-10 25th Feb-5th March; 20th-23rd 100 (47.8) 15 (62.5) March 2010-11 28th Feb-5th March 45 (21.5) 4 (16.6) Total (n) 209 24 236 INDIAN J MAR SCI VOL 45, NO.2 FEBRUARY 2016 flippers and injury on the nostril area which are due to hard cement concrete tetrapods into which turtles unknowingly enter and entrap. However, since, there were no facilities to treat injured marine animals nearby, neither with the local forest office nor with the local veterinary hospital, these injured turtles were therefore released into the sea after rescue from entanglement in the tetrapods. In total, 64 no. of injured turtles during 2008-09, 100 during 2009-10 and45 injured turtles during 2010-11 were observed in the study area. Highest turtle injury and mortality were observed in 2009-10 whereas it was lowest incident during the 2010-11 arribada.
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