over a seven yea.r period are described together with an update of conservation aspects of the nesting population in the area.

Transcription

1 Phuket mar. biol. C ent. Re s. Bull. 67 z (2006) Shortcommunication: REPRODUCTIVE BIOLOGY AND CONSERVATION OF THE OLIVE RIDLEY TURTLE AT PHRA THONG ISLAND, ANDAMAN SEA. THAILAND Monica Aureggit and Supot Chantrapornsyl2 tnaucrates, Onlus, Via Corbetta, Cantu' (CO), Italy zphuket Marine Biolosical Center, P.O.Box 60, Phuket, 83000, Thailand ABSTRACT: Phra Thong Island, located in Phangnga Province, was chosen as a base for a Sea Turtle Project (STP) because of its central geographical position along the Andaman Sea coast. The STP started in 1996 and focused on three different aspects: scientific research and conservation, an educational program in the local schools and development of awareness among tourists. The paper focuses on one of the three nesting turtle species on the island: olive ridley (Lepidochelys olivacea). Data collected over seven years of activities of the STP concerning the reproductive biology of the olive ridley turtle are illustrated and an update of conservation aspects of the nesting population in the area is presented. INTRODUCTION Phra Thong (PT) Island is one of three relatively large islands locatedjust offthe coast of Phang Nga Province along the South West coast of Thailand (Fig. 1). Mangroves cover the east coast of the island, whereas fine sandy beaches (total length 1 km) are located on the west coast. Three fishing villages and two small tourist resorts are located on the island. PT island, together with the two adjacent islands (Ra and Kho Khao), is considered as one of the main marine turtle nesting grounds of the south west coast of Thailand (Chantrapornsyl, 1992a). Three nesting species have been identified in the area: the olive ridley (Lepidochelys olivacea), the leatherback turtle (Dermochelys coriacea) and the green turtle (Chelonia mydas). The nesting season occurs between October and February for the olive ridley and leatherback, with rare olive ridley nesting activity in September and March, whilst the green turtle nests every three years from March to July. In 1996 the STP was started at PT Island with the aim of collecting scientific data on the nesting population; carrying out an education program in the local schools and conducting conservation awareness activities among tourists visiting the island. Reproductive data for the olive ridley turtle over a seven yea.r period are described together with an update of conservation aspects of the nesting population in the area. MATERIALS AND METHODS The 1 km of beach was split into three different sections: beach 1, 2 and 3 (Aureggi, 2000). Partofbeach 1 andbeach 2-3were walked every morning by at least two people during each nesting season (from December to April). The total length of beach I (10 km) was monitored every three days by motorbike. Newly excavated nests and tracks were identified. Eggs were carefully moved from the original location to a safe area near the project base in order for them to be protected during the incubation period. Clutch size, depth of the egg chamber and a sample of 1 eggs per nest were measured. A caliper was used to measure the diameter of the eggs and a spring precision scale (Pesola) was used to weigh them. A wire cage was placed over nests to allow identification of the hatching date and collection of the hatchlings. On the third day after the first emergence, nests were dug in order to estimate the incubation success, evaluating both the hatching and the emergence success. Hatching success refers to the number of hatchlings that hatch out of their egg shell (equals the number of empty egg

2 82 Phuket mar. biol. Cent. Res. Bull. Figure 1. Phra Thong Island, South Thailand. shells in the nest) whereas emergence success refers to the number of hatchlings that reach the beach surface (equals to the number of empty egg shells minus the number of live and dead hatchlings remaining in the nest chamber) (Miller, 1999a). A sample of 20 hatchlings per nest was measured (carapace length (SCL), width (SCW) andweight). Every season, the majority of the hatchlings were released into the sea as soon as they hatched. About 6 hatchlings per season were placed in a tank at the project base on PT Island and about 100 hatchlings were sent to the Phuket Marine Biological Center. These were for the next season's "turtle releasing day" (education program) at PT Island and for the head-starting program respectively. RESULTS The total number of olive ridley nests recorded on PT Island ranged from 3 to 8 between 1996 and2003 (Tablel). One nest in 2003 was recorded on the adjacent island of Kho Khao, where the STP began working in This nest has been included in the analysis as (probably) part of the same nesting population. Between 1996 and2003 the average hatchling success ranged between 7l'/, and 87%o and the average emergence success between 62.7%o and 80% (considering different samples in each season). Details for each season are summarized in Table 2.

3 83 Biology and consewation of the olive ridley turtle Table 1. OR: Olive ridley turtle (Lepidochelys olivacea). Season t996t r998t99 r999t00 2ffi0t0r 200v t03 OR J * Including one nest from Kho Khao Island. Table 2. Hatching success (HS) and emerging success (ES) per season. reggs were collected by a fisherman who kept them in a plastic bag for two days before giving them to the STP.2 eggs were not moved but left in the place where they were originally laid 3 nest excavated at Kho Khao Island. 1998t t t t u12003 HS% ES% HS% ES% HS% ES% HS% ES% HS% ES% I 76 m /) 7l o' n m /)' 68 0r 7l 81 9l 86 1U n % 16 l0 % 1 2 9ff Data on reproductive biology were collected and recorded when possible during the seven years of the project. Table 3 shows the differences between samples in each season. The record of nesting female size refers to one individual found in the season and thereafter used for a satellite tracking study (Chantrapornsyl, 2002). Clutch size was recorded for six consecutive seasons, egg measurements for five seasons, egg chamber size from 1998 to 2003 and incubation period and hatchling measurements from 1999 to DISSCUSSION Data for PT island collected by the Phuket Marine Biological Centre (PMBC) indicates a reduction of 82% in the number of olive ridley nests from 1979 (n: 238) to 1990 (n: 42) (Chantrapornsyl, 1992b). A similar decrease was observed in the data collected from 1996 to 2003, even if the methodologies were different (Fig. 2). Historical data shows a massive sea turtle egg harvest estimated at about 400,000 eggs per year in Thailand, of which 60,000 were from the Phang Nga province (Polunin, 191), where PT island is located. Egg harvesting, the consumption of turtle meat and the hunting of turtles for their shells should be considered as additional contributions to the decrease noted at PT island. The drastic decline of olive ridley nests along the south west coast of Thailand indicates that only a few nesting females have survived in the area. It was thought that moving the eggs from the nest site to a safe, protected location on the beaches ofpt island would have been a successful conservation strategy, since egg poaching is considered to be one of the main causes of the decline. According to Mortimer (1999), a hatchery should be located in a safe place on the beach near the nest in order to minimize physical trauma to eggs during transportation, and to reduce the time interval between eggs beinglaidand theirplanting in the hatchery. Also such a re-location provides

4 Phuket mar. biol. Cent. Res. Bull. Table 3. Reproductive biology of the olive ridley turde. n = number of nests considered; in each nest 1-20 eggs and hatchlings were sampled; EC TOP = egg chamber depth measured from the top of the eggs to the surface level; EC BOT = egg chamber depth from the bottom to the surface level. SD = Standard deviation. REPRODUCTIVE BIOLOGY DATA Season 1997t t /00 Le pi.dochely s olivace a mean SD min-max n mean SD n mean SD min-max n Carapace length of nesting female Carapace width of nesting female Diameter of eggs (cm) Weight of eggs (g) Clutch size Length of incubation (days) 3.' 't r r-r32 48* Carapace length of hatchlings SCL (cm) Carapace width of hatchlings SCW (cm) 3. 0.i Weight (g) r"t EC TOP (cm) EC BOT (cm) 3 0 r 28 t ' n< 21 l Season Lepidochelys olivacea 2000/01 200r/02 mean SD min-max n mean SD min-max n mean SD min-max n Carapace length of nesting female Carapace width of nesting female 68 6 Diameter of eggs (cm) Weight of eccs (g) Clutch size 133 r8.1 rt 'l r0l tt2-r3t 3 Length of incubation (days) ' Carapace length of hatchlings SCL (cm) * Carapace width of hatchlings SCW (cm) ' r Weight (g) r t t3.-2t 3 EC TOP (cm) EC BOT (cm) r-2 3 2'

5 Biolog,t and conservation of the olive ridley turtle 6) opportunity for embryos and hatchlings to imprint on the nesting beach and to facilitate hatchling release. Hatching success gives an evaluation of the success of egg incubation and is typically high (80% or more) unless external factors (e.g. predation, environmental changes, microbial infection, etc.) intewene (Miller, 1999b).In India the hatching success ofreburied eggs recorded in 2001/2002 was variable and ranged from 0 to 39o/o (Kurian and Nayak, 2003). This low success was considered a result ofthe depth and shape ofthe nest cavity in the hatchery. In addition the sand texture was probably dissimilar to the original nest and not appropriate (Kurian and Nayak, 2003). On PT Island, hatching success recorded in ranged between 7 3. and 87.3% (Chantrapornsyl, 1992a), and subsequently from 1996 to 2003 between 71.9 and87.3%. This indicated that eggs were moved carefully enough to obtain the same rate of success (70-80%) as recorded with natural hatching along the West coast of Thailand in the past (Phasuk and Rongmaungsart, 1973). ln fact, in the present project when nests were moved an attempt was made to emulate the natural nesting area as much as possible and training was given by an expert to volunteers and local people in order to avoid any unnecessary interference with the incubation of newly laid eggs. The average clutch size ofolive ridley nests recorded between 1996 and2003 (118.8: SD : 13,2) was higher than that recorded between 1980 and 1990 (111.89; SD : 9.9) on PT Island (Chantraporn syl, 1 992b),showing a variation over the last 30 years. It was also higher than the clutch size reported in Surinam (116) (Schultz,197), India (114.7) (Valliappan and Whitaker, 1974 in Hirth, 1980) and Bangladesh (l1.3) (Islam, 2002), and than the value (109.9; SD: 1.8) reported for I I populations by Miller (1999b). The number and size of eggs represent the result of an adaptive compromise for survival (Mille1 1999b), and their variations are attributed to the sizelage of the nesting female (Schultz, 197). The average diameter of eggs recorded between 1996 and 2003 and between 1980 and 1990 were similar at 38 mm (SD: 0.2) and 38.3 mm (SD : 0.6), respectively (Chantrapornsyl, 1992b), whereas the average weight was slightly different at (SD : 1.3) and (SD : 1.98) respectively. Thai eggs are similar in size to other olive ridley eggs recorded in Surinam (O : 40) (Schultz, 197), Sri Lanka (A : 40.) (Dekaniygala, 1939 in Hirth 1980) and in Bangladesh (O: 38.) (Islam, 2002). The average incubation period in 1981 and 1982 on PT island was 2 days (Chantrapornsyl, 1992b) whereas between 1998 and 2003 was 48 days. The length of the incubation period is dependent on temperature (Miller, 1999b) and can therefore vary between seasons. Hatchling catapace length on PT Island, averaged 43 mm (SD : 0.1), is similar to that of hatchlings in Surinam (42 mm) (Schultz, 197) and in Sri Lanka (42.8 mm) (Dekaniygala,1939 in Hirth 1980) and smaller than those inlndia (47. 7 mm) (Valliappan and Whitaker, 19'74 in Hifth, l e80). The average weight of hatchlings at 18g (SD : 0.8) on PT is similar to the l7g reported by Miller (1999b). An update of conservation aspects: The STP has contributed to the decrease in egg poaching activity (Aureggi et al.,2002), the protection of all nests laid, the safe release of more than 2000 hatchlings into the sea and the rescue of several animals incidentally caught in fishing nets (Aureggi and Chantrapornsyl, 2002). The project also provides tourists visiting the island with information by the use of a display area where they can learn about sea turtles, conservation and other wildlife of the island. Slide shows, talks and demonstrations are also put together for visitors. Conservation strategies at PT island are applied in order to protect as many eggs as possible and maintain the status of the nesting population with a possible view to increasing their numbers in future generations. One ofthe main threats, egg poaching. has nearly been eliminated through conservation education but intense fishing activities near the nesting beaches during the breeding season and

6 86 Phuket mar. biol. Cent. Res. Bull. plans for tourism development are threatening the survival of the small nesting population. To prevent further decimation of this population a long-term education program of fishermen, and lobbying activities at both provincial and national government levels to limit tourism development, are needed. It is very important to assess the interaction between fishing efforts and sea turtles. Different fishing equipment (trawls, lift nets, dredge nets, gillnets, fishing traps, long lines, etc.) may induce different capture and mortality rates. In addition, to collect information on the interaction between fisheries and turtles, a rescue center at PT Island, involving the local community, would help reduce mortality rate by rescuing injured animals and releasing them into the sea. ACKNOWLEDGEMENTS The authors would like to thank Carole Beauclerk for her volunteer work in coordinating the educational program and all the volunteers that took part in the project. Special thanks are due to Lory Follador for her logistic support and tclthe local community for their participation and help. Thanks to Katie Jones for assistance in manuscript revision. REFERENCES Aureggi, M Progress reporl No.l "Pilot Project to Establish the Phang Nga Focal Point for Sea Turtle Conservation at Phra Thong Island" Submitted to National Research Council Thailand. 1 p. Aureggi, M. and S. Chantrapornsyl Is a Long Term Educational Program Effective to Prevent Extinction? Proceeding of the 3'd SEASTAR2000 Workshop, Bangkok Dec pp.3l- JJ. Aureggi, M., G. Gerosa and S. Chantrapornsyl. (in press). Elimination of Egg Poaching Activity at Phra Thong Island, Thailand. Proceedings of the First Italian Meeting on Sea Turtle Biology and Conservation. Policoro, Italy. Chantrapornsyl, S. 1992a. Artificial incubation and embryonic development of olive ridley eggs (Lepidochelys olivacea, Eschscholtz). Phuket mar. biol. Cent. Res. Bull. 7: Chantrapornsyl, S. 1992b. Biology and Conservation Olive Ridley Turlles (Lepidochelys olivacea) in the Andaman Sea, Southern Thailand. Phuket mar. biol.cent. Res. Bull. 7: l-66. Hidh, H.F Some Aspects of the Nesting Behavior and Reproductive Biology of Sea Turtles. Am. Zool.20: Islam, M.Z Marine Turtle Nesting at St. Martin's Island, Bangladesh. MTN: 96: Miller, J.D. 1999a. Determining Clutch Size and Hatching Success. In: Eckert K.L., K.A. Bjorndal, F.A. Abreu-Grobois and M. Donnelly (eds.). Research and Management Techniques for the Conservation of Sea Turtles. IUCN/SSC Marine Turtle Specialist Group Publication No.4. Miller, J.D. 1999b. Reproduction in Sea Turtles. In: Lutz, P.L. and J.A. Musick (eds.). The Biology of Sea Turtles. CRC Press. pp. l-81. Mortimer, J.A Reducing Threats to Eggs and Hatchlings: Hatcheries. In: K.L. Eckert, K.A. Bjorndal, F.A. Abreu-Grobois, M. Donnelly (eds.). Research and Management Techniques for the Conservation of Sea Turtles. IUCN/SSC Marine Turtles Specialist Group. Publ. No.4. pp. 17* 178. Phasuk, B. and S. Rongmaungsart Growth Studies on the Olive Ridley, Lepidochelys olivacea, in Captivity and the Effect of Food Preference on Growth. Phuket mar. biol. Cent. Res. Bull. 1: Polunin, N.V.C Sea Turtles: Reports on Thailand, West Malaysia and Indonesia with Synopsis of Data on the Conservation Status in the Indo West Pacific Region. Unpubl. report.

7 87 Biology and conservation of the olive ridley turtle Kurian, A. and V.N. Nayak Influence of Environmental Factors on the Hatching Success of Olive Ridley Turtles: A Preliminary Study. Kachhapa Newsletter 8: Schulz, I.P Sea Turtles Nesting in Surinam. Rijksmuseum Van Natuurliklijke Histories, Leiden, Netherland. 143 p. Manus cript received : February 2 00 Accepted: October 200