Phuket mar. biol. C ent. Re s. Bull. 67 z 8 1-87 (2006)

Shortcommunication:

REPRODUCTIVE BIOLOGY AND CONSERVATION OF THE OLIVE RIDLEY TURTLEAT PHRA THONG ISLAND, ANDAMAN SEA. THAILAND

Monica Aureggit and Supot Chantrapornsyl2

tNaucrates, Onlus, Via Corbetta, 11-22063 Cantu' (CO), ItalyzPhuket 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 TurtleProject (STP) because of its central geographical position along the Andaman Sea coast. The STPstarted in 1996 and focused on three different aspects: scientific research and conservation, aneducational program in the local schools and development of awareness among tourists. The paperfocuses 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 inthe area is presented.

INTRODUCTION

Phra Thong (PT) Island is one of threerelatively large islands locatedjust offthe coast ofPhang Nga Province along the South West coastof Thailand (Fig. 1). Mangroves cover the east

coast of the island, whereas fine sandy beaches(total length 15 km) are located on the west coast.

Three fishing villages and two small tourist resortsare located on the island. PT island, together withthe two adjacent islands (Ra and Kho Khao), is

considered as one of the main marine turtle nestinggrounds of the south west coast of Thailand(Chantrapornsyl, 1992a) .

Three nesting species have been identified inthe area: the olive ridley (Lepidochelys olivacea),the leatherback turtle (Dermochelys coriacea) andthe green turtle (Chelonia mydas). The nestingseason occurs between October and February forthe olive ridley and leatherback, with rare oliveridley nesting activity in September and March,whilst the green turtle nests every three years fromMarch to July.

In 1996 the STP was started at PT Island withthe aim of collecting scientific data on the nestingpopulation; carrying out an education program inthe local schools and conducting conservationawareness activities among tourists visiting theisland. Reproductive data for the olive ridley turtle

over a seven yea.r period are described togetherwith an update of conservation aspects of thenesting population in the area.

MATERIALS AND METHODS

The 15 km of beach was split into threedifferent sections: beach 1, 2 and 3 (Aureggi,2000). Partofbeach 1 andbeach 2-3were walkedevery morning by at least two people during each

nesting season (from December to April). The totallength of beach I (10 km) was monitored everythree days by motorbike. Newly excavated nests

and tracks were identified. Eggs were carefullymoved from the original location to a safe area

near the project base in order for them to beprotected during the incubation period. Clutch size,

depth of the egg chamber and a sample of 15 eggsper nest were measured. A caliper was used tomeasure the diameter of the eggs and a springprecision scale (Pesola) was used to weigh them.

A wire cage was placed over nests to allowidentification of the hatching date and collectionof the hatchlings. On the third day after the firstemergence, nests were dug in order to estimatethe incubation success, evaluating both the hatching

and the emergence success. Hatching success

refers to the number of hatchlings that hatch outof their egg shell (equals the number of empty egg

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 hatchlingsremaining in the nest chamber) (Miller, 1999a). Asample of 20 hatchlings per nest was measured(carapace length (SCL), width (SCW) andweight).Every season, the majority of the hatchlings werereleased into the sea as soon as they hatched. About6 hatchlings per season were placed in a tank at

the project base on PT Island and about 100

hatchlings were sent to the Phuket MarineBiological Center. These were for the next season's

"turtle releasing day" (education program) at PT

Island and for the head-starting programrespectively.

RESULTS

The total number of olive ridley nests recordedon PT Island ranged from 3 to 8 between 1996and2003 (Tablel). One nest in 2003 was recordedon the adjacent island of Kho Khao, where the STP

began working in 2001. This nest has beenincluded in the analysis as (probably) part of thesame nesting population.

Between 1996 and2003 the average hatchlingsuccess ranged between 7l'/, and 87%o and theaverage emergence success between 62.7%o and

80% (considering different samples in each

season). Details for each season are summarizedin Table 2.

83

Biology and consewation of the olive ridley turtle

Table 1. OR: Olive ridley turtle (Lepidochelys olivacea).

Season t996t97 199798 r998t99 r999t00 2ffi0t0r 200v02 2002t03

JOR

* Including one nest from Kho Khao Island.

Table 2. Hatching success (HS) and emerging success (ES) per season. reggs were collected by afisherman who kept them in a plastic bag for two days before giving them to the STP.2 eggs were notmoved but left in the place where they were originally laid 3 nest excavated at Kho Khao Island.

1998t1999 1999t2000 2000t2001 2001t2002 20u12003

HS% ES% HS% ES% HS% ES% HS% ES% HS% ES%

53

45

903

15

29ff

16

l0%

85

83

%

n87

79

82

95

85

68

0r

7l81

9l86

1U

m56

78

83

/)

97

79

78

I76

7lo'nm91

88

/)'

Data on reproductive biology were collectedand recorded when possible during the seven yearsof the project. Table 3 shows the differencesbetween samples in each season. The record ofnesting female size refers to one individual foundin the 2001102 season and thereafter used for a

satellite tracking study (Chantrapornsyl, 2002).Clutch size was recorded for six consecutiveseasons, egg measurements for five seasons, eggchamber size from 1998 to 2003 and incubationperiod and hatchling measurements from 1999 to2003.

DISSCUSSION

Data for PT island collected by the PhuketMarine Biological Centre (PMBC) indicates a

reduction of 82% in the number of olive ridleynests from 1979 (n: 238) to 1990 (n: 42)(Chantrapornsyl, 1992b). A similar decrease wasobserved in the data collected from 1996 to 2003,even if the methodologies were different (Fig. 2).

Historical data shows a massive sea turtle eggharvest estimated at about 400,000 eggs per yearin Thailand, of which 60,000 were from the PhangNga province (Polunin, 1915), where PT island islocated. Egg harvesting, the consumption of turtlemeat and the hunting of turtles for their shellsshould be considered as additional contributionsto the decrease noted at PT island.

The drastic decline of olive ridley nests alongthe south west coast of Thailand indicates thatonly a few nesting females have survived in thearea. It was thought that moving the eggs fromthe nest site to a safe, protected location on thebeaches ofPT island would have been a successfulconservation strategy, since egg poaching isconsidered to be one of the main causes of thedecline. According to Mortimer (1999), a hatcheryshould be located in a safe place on the beach nearthe nest in order to minimize physical trauma toeggs during transportation, and to reduce the timeinterval between eggs beinglaidand theirplantingin the hatchery. Also such a re-location provides

Phuket mar. biol. Cent. Res. Bull.

Table 3. Reproductive biology of the olive ridley turde. n = number of nests considered; in each nest 15-20

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

Le pi.dochely s olivace a mean SD min-max n mean SD n mean SD min-max n

1997t98 1998t99 1999/00

Carapace length of nestingfemaleCarapace width of nestingfemaleDiameter of eggs (cm)

Weight of eggs (g)

Clutch size

Length of incubation(days)

Carapace length ofhatchlings SCL (cm)

Carapace width ofhatchlings SCW (cm)

Weight (g)

EC TOP (cm)

EC BOT (cm)

3.'7 0.1 3.5-4 1

30 2.3 25-33.5 1

115 15.5 104-126 2

3.7 0.1

29.'t 1 .0

123 7.0

50

3.4-3.8

29 .r-30.5

1 r5-r32

48*52

5

5

5

5

35

50

107 16.5

50

0.1

0.i

4.3

3.5

r"t 1.0

5 28r 28

t4225-30

3'7-45

82-128 6

48-52 4

4.2-4.4 4

3 .2-3.6 4

16-18 4

n< 21 l

37-52 4

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

Diameter of eggs (cm)

Weight of eCCS (g)

Clutch size

Length of incubation (days)

Carapace length ofhatchlings SCL (cm)

Carapace width ofhatchlings SCW (cm)

Weight (g)

EC TOP (cm)

EC BOT (cm)

3.8 0.1 3.7-4 3

31 1.0 28-33 3

133 r8.1 rt6-153 3

47 .5 47 -48 2

4.2 0.1 4-4.5 3

3.5 0.1 3.3-3.6 3

18.6 0.5 r1-19.7 3

25 20-28 3

40 38-42 3

3 .6 0. 1 3 .4-3 .'7

68

65

3.9 0.1

33.4 0.9

112 12.'l

47.6

4.3 0.0

3.8-3.9

32.4-33.9

r0l-125

4'1-48

4.1*4.5

3.8 0.6

34 1.1

121..5 9.5

47.0

4.2 0.2

3.8-4 2

30-39 2

tt2-r3t 3

46-48 3

3.3-4.4 3

3.r-3.6 3

t3.5-2t 3

24-31.5 3

36.5-50 3

0.43.4

19.0 0.7 17 -20

29 23-34

5 1 5r-52

3 t7.5 0.9

3 2'7.4

3 41.8

6)

Biolog,t and conservation of the olive ridley turtle

opportunity for embryos and hatchlings to imprinton the nesting beach and to facilitate hatchlingrelease.

Hatching success gives an evaluation of thesuccess of egg incubation and is typically high(80% or more) unless external factors (e.g.predation, environmental changes, microbialinfection, etc.) intewene (Miller, 1999b).In Indiathe hatching success ofreburied eggs recorded in2001/2002 was variable and ranged from 0 to 39o/o

(Kurian and Nayak, 2003). This low success wasconsidered a result ofthe depth and shape ofthenest cavity in the hatchery. In addition the sandtexture was probably dissimilar to the original nestand not appropriate (Kurian and Nayak, 2003). OnPT Island, hatching success recorded in 1981-82ranged between 7 3.5 and 87 .3% (Chantrapornsyl,1992a), and subsequently from 1996 to 2003between 71.9 and87.3%. This indicated that eggswere moved carefully enough to obtain the samerate of success (70-80%) as recorded with naturalhatching along the West coast of Thailand in thepast (Phasuk and Rongmaungsart, 1973). ln fact,in the present project when nests were moved anattempt was made to emulate the natural nestingarea as much as possible and training was givenby an expert to volunteers and local people in orderto avoid any unnecessary interference with theincubation of newly laid eggs.

The average clutch size ofolive ridley nestsrecorded between 1996 and2003 (118.58: SD :13,2) was higher than that recorded between 1980and 1990 (111.89; SD : 9.59) on PT Island(Chantraporn syl, 1 992b),showing a variation overthe last 30 years. It was also higher than the clutchsize reported in Surinam (116) (Schultz,1975),India (114.7) (Valliappan and Whitaker, 1974 inHirth, 1980) and Bangladesh (l15.3) (Islam, 2002),and than the value (109.9; SD: 1.8) reported forI I populations by Miller (1999b). The number andsize of eggs represent the result of an adaptivecompromise for survival (Mille1 1999b), and theirvariations are attributed to the sizelage of thenesting female (Schultz, 1975).

The average diameter of eggs recordedbetween 1996 and 2003 and between 1980 and

1990 were similar at 38 mm (SD: 0.2) and 38.35mm (SD : 0.65), respectively (Chantrapornsyl,1992b), whereas the average weight was slightlydifferent at 31.69 (SD : 1.3) and 33.199 (SD :1.98) respectively. Thai eggs are similar in size toother olive ridley eggs recorded in Surinam (O :40) (Schultz, 1975), Sri Lanka (A : 40.5)(Dekaniygala, 1939 in Hirth 1980) and inBangladesh (O: 38.5) (Islam, 2002).

The average incubation period in 1981 and1982 on PT island was 52 days (Chantrapornsyl,1992b) whereas between 1998 and 2003 was 48days. The length of the incubation period isdependent on temperature (Miller, 1999b) and cantherefore vary between seasons.

Hatchling catapace length on PT Island,averaged 43 mm (SD : 0.1), is similar to that ofhatchlings in Surinam (42 mm) (Schultz, 1975)and in Sri Lanka (42.8 mm) (Dekaniygala,1939 inHirth 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 byMiller (1999b).

An update of conservation aspects:The STP has contributed to the decrease in

egg poaching activity (Aureggi et aL.,2002), theprotection of all nests laid, the safe release of morethan 2000 hatchlings into the sea and the rescueof several animals incidentally caught in fishingnets (Aureggi and Chantrapornsyl, 2002). Theproject also provides tourists visiting the island withinformation by the use of a display area wherethey can learn about sea turtles, conservation andother wildlife of the island. Slide shows, talks anddemonstrations are also put together for visitors.

Conservation strategies at PT island are appliedin order to protect as many eggs as possible andmaintain the status of the nesting population witha possible view to increasing their numbers in futuregenerations. One ofthe main threats, egg poaching.has nearly been eliminated through conservationeducation but intense fishing activities near thenesting beaches during the breeding season and

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-termeducation program of fishermen, and lobbyingactivities at both provincial and national governmentlevels to limit tourism development, are needed.

It is very important to assess the interactionbetween fishing efforts and sea turtles. Differentfishing equipment (trawls, lift nets, dredge nets,gillnets, fishing traps, long lines, etc.) may inducedifferent capture and mortality rates. In addition,to collect information on the interaction betweenfisheries and turtles, a rescue center at PT Island,involving the local community, would help reduce

mortality rate by rescuing injured animals andreleasing them into the sea.

ACKNOWLEDGEMENTS

The authors would like to thank CaroleBeauclerk for her volunteer work in coordinatingthe educational program and all the volunteers thattook part in the project. Special thanks are due toLory Follador for her logistic support and tclthelocal community for their participation and help.Thanks to Katie Jones for assistance in manuscriptrevision.

REFERENCES

Aureggi, M. 2000. 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.

15 p.

Aureggi, M. and S. Chantrapornsyl. 2003. Is a Long Term Educational Program Effective to Prevent

Extinction? Proceeding of the 3'd SEASTAR2000 Workshop, Bangkok 16119 Dec.2002. pp.3l-JJ.

Aureggi, M., G. Gerosa and S. Chantrapornsyl. (in press). Elimination of Egg Poaching Activity at PhraThong 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. 57: 41-50.Chantrapornsyl, S. 1992b. Biology and Conservation Olive Ridley Turlles (Lepidochelys olivacea) in

the Andaman Sea, Southern Thailand. Phuket mar. biol.Cent. Res. Bull. 57: 5l-66.Hidh, H.F. 1980. Some Aspects of the Nesting Behavior and Reproductive Biology of Sea Turtles. Am.

Zool.20: 507-523.Islam, M.Z. 2002. Marine Turtle Nesting at St. Martin's Island, Bangladesh. MTN: 96: 19-21.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. 5l-81.Mortimer, J.A. 1999. 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. 175*178.

Phasuk, B. and S. Rongmaungsart. 1973. 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: 1-14.

Polunin, N.V.C. 1975. 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.

87

Biology and conservation of the olive ridley turtle

Kurian, A. and V.N. Nayak. 2003. Influence of Environmental Factors on the Hatching Success ofOlive Ridley Turtles: A Preliminary Study. Kachhapa Newsletter 8: 8-11.

Schulz, I.P. 197 5. Sea Turtles Nesting in Surinam. Rijksmuseum Van Natuurliklijke Histories, Leiden,Netherland. 143 p.

Manus cript received : February 2 00 5

Accepted: October 2005