Sea Turtles at Dungsha Tao (Pratas Island) and Taipin Tao (Spratly Islands), South China Sea

 Cheng, I-Jiunn

Abstract

More than 90 % of sea turtle populations of China are distributed in the South China Sea. The military forces from claimant nations occupy most of the islands, and the political instability in the region complicates sea turtle surveys and implementation of conservation measures. Very little is known about the nesting and feeding populations of sea turtles in the South China Sea. Surveys were carried out in July 1994 to Pratas Island and in April 1995 to Taipin Tao of the Spratley Archipelago. The 12-day survey on Pratas Island found that very few hawksbills and no greens nested on the island. The nesting season was reported to occur in the summertime. A survey on Pratas Atoll in 1998 revealed severe reef bleaching in the lagoon region, suggesting substantial destructive fishing using KCn solution and dynamite, which may impact feeding habitats of turtles.

A 5-day survey on Taipin Tao indicated that both hawksbills and greens nested on the island There were more nesting greens than the hawksbills. Questionnaire interviews determined that the nesting season lasts year-round The nesting environment on adjacent islands has been severely destroyed by military forces from other nations. Pirates and illegal fishing are among other serious problems in the area.

Both surveys revealed that the protection of nesting beaches on the islands is insufficient to conserve turtle populations. It is strongly recommended that ASEAN should expand their sea turtle conservation program to include all nations who deploy military forces on the islands in the South China Sea, and should ivork cooperatively to save the declining sea turtle populations.

Introduction

According to Liang et al. (1990), more than 90 % of the sea turtle populations of China are distributed in the South China Sea (Fig. 1). However, the political instabitity brought about conflicting by the claims to the Sprately islands by nations surrounding the South China Sea complicates sea turtle surveys and conservation measures. The military forces from claimant nations occupy most of the islands. The hostile attitude by the military toward visitors revents surveys on sea turtles, both on the nesting beaches and in the nearshore waters. For this reason, very little is known about the nesting and feeding populations of sea turtles in the region.

Previous studies carried out at Dungsha Tao include substrate structure (Hwang et al. 1975), marine flora (Jung 1975), coral reef fishes and mollusks (Yang et al. 1975), deep sea fishes (Hwang & Yang 1983), benthic algae (Fang & Li 1994) and marine ecology (CKCG 1980). Although two studies were related sea turtles in the region (Liang et al. 1990, Hwang et al. 1991), no information on the nesting ecology are available and only a few details on population dynamics are presented. The only recent reports are underwater photographs of hawksbill turtles taken during a South China Sea Marine Biology Survey, led by the Institute of Zoology, Academa-Sinica in April 1994. In July 1994, the military forces on the island had also reported the rescue of a "big" sea turtle entangled in longline fishing gear.

Studies at Taipin Tao include research on coral reefs, coralline fishes, plankton and nekton, mollusks, benthic algae, water quality, terrestrial flora and birds (Liu 1975, Wu 1981, Chang et al. 1981, Fang & Li 1994). Despite the fact that the island has long been known as a nesting site for sea turtles, no scientific studies of turtles have been conducted to date.

Nan-sha Archipelago has long been recognised as a major sea turtle nesting area in the South China Sea. Despite nearly 40 years of occupancy, the forests and beaches remain relatively untouched. With the existing martial law, no artificial lights are allowed at night. These and other rules promote suitable nesting conditions for the sea turtles. Nesting turtles have faced serious threats in the past, including egg collection and slaughter (soldiers once killed females for meat during supply shortage). Fortunately the situation has improved recently, after the Navy provided better supply services and emphasised environmental conservation on the islands. Today, no eggs are collected and the morning beach patrols rescue any females trapped in defence trenches. However, existing beach barricades still prevent the turtles from reaching nest sites above the high tide line on some beaches.

Fig. 1: Map of South China Sea, indicating the location of the sea turtle nesting sites in the territories of Republic of China. Symbols denote the species of nesting sea turtles.

Political instability in the region complicates conservation measures. Marines from China, Philippine, Malaysia, Vietnam, Brunei and Taiwan occupy the archipelagos. Malaysia and Vietnam have constructed airfields on some islands. It has been reported that China has filled-in several submerged atolls with cement, turning them into "strategy islands". Others, such as Vietnam, have constructed buildings on every inch of soil on the occupied island. In addition, many countries claim waters within the archipelago as part of their Exclusive Economic Zone (see Gomez 1996). Pirates and illegal fishing are among the problems plaguing the region. For example, a fishing vessel from Taiwan was robbed recently, and the first mate was killed by pirates in the vicinity of Taipin Tao.

A review of the literature, and interviews with island inhabitants suggest that Dungsha Tao and Taipin Tao may be among the few remaining islands that still maintain vascular floral growth, and support sea turtle nesting. The purpose of this study was to gather preliminary information on the species of sea turtles nesting on these two islands and to determine their nesting site distribution.

Materials and Methods

With the collaboration of Council of Agriculture and the Defence Department, a 12-day expedition to Dungsha Tao was conducted in July 1994, and a 15-day expedition to Taipin Tao in April 1995. Two survey methods were employed. First, at least 100 military staff on Dungsha Tao and Taipin Tao that had been stationed on the islands for more than four months were questioned about the species of sea turtle nesting on the island as well as the location and timing of the nesting efforts. The potential nesting beaches on both islands were divided into different sections: on Dungsha Tao, the beaches were divided into the south shore (S), north shore (N) and lagoon (L) sections because of the lack of topographic discontinuity or history of emergence records (Fig 2); on Taipin Tao, the beaches were divided into nine smaller sectors because of the higher emergence frequency, labelled AI (Fig. 3).

Secondly, all potential nesting beaches were inspected twice each night from 1900 to 0500 and again at dawn from 0600 to 0700 in search of nesting females and fresh nesting tracks. Turtles encountered on beaches were tagged with an Inconel tag (National Band and Tag Co., Style No. 681) on each front flipper for identification. A small piece of tissue was also collected for the DNA analysis to determine if each belonged to discreet breeding stocks. Occasionally, beaches were also inspected during the daytime. On Dungsha Tao, three cruises were also conducted 2-3 km off the south shore to search for swimming turtles.

The Study Sites

Dungsha Tao - Dungsha Tao, or Pratas Island (20^°42.5'N; 1 16^°43.5'E), is the northernmost coral island in the South China Sea. Located at the western extreme of Dungsha Atoll, the island is 2,500 m long and 865 m wide with an area of 1.74 km², of which 0.64 km² is an internal lagoon no deeper than 1.5 m (Fig. 2). The island consists of moderately sorted coarse grains with an interstitial water content of 9.8 % (by weight). The climate is subtropical marine, dominated by trade winds which blow from the southwest during May to August, and from the northeast during November to March. Total annual precipitation is 1,132.5 mm, with a maximum in June (226 mm) and minimum in December (3.3 mm). Surface seawater temperature averages 25^°C, with a maximum in June (29-30^°C) and a minimum in January (22^°C). Tides are diurnal, with a maximum amplitude of 1.21 m (Central Climate Bureau, 1994). Military forces from the Republic of China have been stationed on Dungsha Tao since 1945. On average 300-500 Marines live in various buildings on the island.

Fig.2: Map of Dungsha Tao or the Pratas Island. The shaded areas are the main nesting sites for hawksbill turtles.

Taipin Tao - The Nan-sha Archipelago or the Spratley Islands is composed of 102 coralline islands, atolls and shoals. Taipin Tao (10º22'N; 114º22'E,) is among the largest of the islands, measuring 1,365 m long and 360 m wide with an area of 0.48 km² (Fig. 3). Taipin Tao is forested with lowland tropical rainforest and reaches an average topographic height of 3.8 m (Fang and Li 1994).

 
Fig. 3. Map of Taipin Tao in the Spratley Archipelago. The fringe outskirts are coral reefs. Letters denote the beach sections where surveys were carried out.

The island is composed of sand covered with guano, consisting mainly of moderate to well sorted coarse grained sand with an interstitial water content of 6 % (by weight). The climate is tropical marine dominated by trade winds, which blow from the southwest during May to October, and from the northeast during November to March. Local current patterns are influenced primarily by the trade winds. Tides are diurnal, with a maximum amplitude of 1.2 m (UNEP/IUCN 1988). Security forces from the Republic of China have occupied Taipin Tao since 1948. In general, 100-150 Marines are stationed on the island.

Results

Dungsha Tao - According to Chinese security forces, both "Daimo" (the common Chinese name for the hawksbill turtle Eretmochelys imbricata) and "bit" (green turtle Chelonia mydas) nest on both the northern and southern beaches. The Marines also reported that hatchlings that emerged from nests on the northern beaches crawled toward streetlights during September and October. Nesting was only observed on 20 July, when two sets of fresh tracks were found leading from the sea to bushes in the supralittoral zone in the south shore section. The turtle crawled through a barbed wire barricade to reach the nesting site. The tracks measured 60 cm and 82 cm wide. On 21 July, a hawksbill turtle (90 cm curved carapace length, 84 cm straight carapace length) was encountered after it nested under a bush in the south shore section. In order to reduce the change of either Marines or dogs digging into the nest, the nest was undisturbed and left in situ. No further nesting activity was observed, but two possible nest sites were also found on the south shore section, identified through the nesting pit depressions.

Taipin Tao - Among 35 interviewees, 20 had been on the island for more than a year. Most of them were solders who guard the shoreline during the night. They reported that hawksbill and green turtles nest on the southern and eastern beaches of Taipin Tao. They estimated that 10 to 100 nests were laid each year around with a peak season during June to November. Most Marines had observed 25 to 35 nesting females during their service period. Because individual females may nest multiple times in a season, the total size of the nesting population was not known. Questionnaire interviews also indicated that, except on section B where the harbour was located, turtles emerged all around the island, with a higher number nesting on sections D to F, where few buildings were built (Table I).

Daytime beach surveys revealed four old nesting tracks and three false crawls; all were located on the southeast coast. Among them, two were by hawksbills and five by greens, as determined by track width and characteristic crawling gaits. The tracks appeared to be at least a few days old. No nesting was observed during the first four nights of the survey, but on 14 April two green turtles were encountered when returning back to the sea in section E. They measured 100 cm and 96 cm curved carapace length.

Table I: The emergence frequency of sea turtles in different sections on Taipin Tao (interview sampling size. 35 persons)

Discussion

Beach surveys and questionnaire interviews on both islands established that both green and hawksbills nest on the beaches, and preferred to emerge where little human interference occurred. These results are consistent with other studies around the world (Carr & Carr 1972, Hays & Speakman 1993, Wang & Cheng 1999) and suggest the importance of maintaining the natural state of nesting beaches as conservation measures for sea turtle nesting.

In Chinese customs the sea turtle is a symbol of longevity and, for that reason, often revered. At times the Commander of Navy base on Dungsha Tao has given direct orders to the Marines to protect the turtles. Nonetheless, the turtle populations in this region are reported to be declining. Senior officers recalled densely-populated nesting beaches on the island 10 to 20 years ago. Liang et al. (1990) reported that more than 2000 sea turtles have been slaughtered in the waters of Dungsha Tao since 1986. Today, there are very few turtles nesting on the island. Because of political instability around the island, relatively few fishermen from Taiwan fish in this area. However, fishermen from Hong Kong, Malaysia, People's Republic of China, Philippine, and Vietnam fish in the waters around Dungsha Tao. Fishing methods include the use of bottom trawls fitted with chain rollers, in addition to cyanide and blast fishing, even though these have been outlawed in Taiwan. During a routine nearshore patrol in 1998 the Navy confiscated more than 200 kg of KCn and numerous blast fishing devices which fishermen had been using to poison and catch fish. These activities have had a devastating impact on local marine organisms and coral reefs, and could pose a threat to the foraging habitats of marine turtles.

Studies conducted in 1998 revealed serious impact of illegal fishing on the coral reef ecosystem. In an International Workshop on the Migration, Foraging Habitats and Nesting Ecology of Marine Turtles in Taiwan, sea turtle experts from Philippine, Hong Kong, United States, Malaysia, China, United Arab Emirates and Japan expressed their deep concern over the plight of sea turtles in the Dungsha Tao region. It was suggested that the development of ecotourism may be a practical method to protect coral reefs, and thus the sea turtle population.

The slaughter and incidental capture of sea turtles are well-known and serious threats throughout the South China Sea (Liang et al. 1990, Nishemura 1990). Despite political differences, these problems are shared by all nations in the region. It is impossible to determine the existing status of sea turtles and implement conservation measures in the South China Sea without the cooperation of all parties. Therefore, it is strongly recommended that ASEAN (Association of Southeast Asian Nations) expand their sea turtle conservation programs to include all states who deploy security forces to islands in the South China Sea. Satellite telemetry of green turtles is scheduled to be conducted on Taipin Tao in the spring of 2000, and we are hopeful of getting the chance for the sea turtle experts to work cooperatively with us to save our declining sea turtle populations.

Acknowledgements

The author would like to thank Mr. Sun-Hon Tsu and Mr. Jen-Chan Wang for their assistance on the field trips to Dungsha Tao and Taipin Tao. The Marines on both islands provided much assistance and a pleasant atmospheres which was highly appreciated. The author also would like to thank the Council of Agriculture and Defence Department of the Republic of China for their administrative assistance on both expeditions.

References

Carr, A. & M.H. Can, 1972. Site fidelity in the Caribbean green turtle. Ecology 53: 425-429.

Central Climate Bureau, 1994. 1994 Climate Data, Dungsha Tao.

Chang K-H., R-Q. Jan & C-S. Hua, 1981. Scientific note: Inshore fishes at Tai-pin Island (South China Sea). Bull. Inst. Zool. Academia Sinica 20: 87-93.

Council of Kaoshiung City Government, 1980. The investigation of the marine ecology resources of the Dungsha waters. Kaoshiung, Taiwan, R.O.C.: 61pp.

Fang, L-S. & J-C. Li, 1994. Report on the Ecological Environment of South China Sea. Council of Agriculture Tech. Memo. 83-Sci-2. 1 5-Fish-13: 471pp.

Gomez, E.D., 1996. Sea turtles in the cross-fire. Marine Turtle Newsletter 72: 19-20.

Hays, G.C. & J.R. Speakman, 1993. Nest placement by the loggerhead turtle, Caretta caretta. Animal Behaviour 45: 47-53.

Hwang, C-C., T-Y. Xiang & W-X. Yan, 1991. The status of research and conservation of marine turtles in China. In: Proc. Intel. Sea Turtle Conference Himeji City Aquarium, Hiwasa-Cho, Toku Shima Prefecture, Japan, 30 July-3 August 1988: 101-102.

Hwang, J-W. & J-J. Yang, 1983. The deep-sea fishes of the Dungsha Waters. In The Study of South China Sea Marine Biology. Guangdong, China, PROC.: 234- 255.

Hwang, J-W., W-S. Jwang & Z-C. Chen, 1975. Substratum investigation. In: The Synoptic Investigation of Dungsha Tao. Institute of Oceanography, National Taiwan University, Taipei, Taiwan, R.O.C.: 21-33

Liang, W-L., J-L. Dai, C-W. Liu, W-S. Liu, J-S. Wein, H-J. Sung, T-T. Chen, I-Z. Chen, Y-K. Shu, S-J. Lu, Z-S. Chang, C-Z. Chang & J-Z. Lin,·l990. The investigation of sea turtle resources in the South China Sea, and the development of the artificial hatching techniques of the sea turtles. Report on the Conservation Stations of South Sea Turtle Resources, Guangdong Province, China, P.R.O.C: 137pp.

Liu, J-S., 1975. Report on the fish and mollusks fauna community of Taipin Tao, South China Sea. .J. China Fisheries 293: 19-21.

Navy Meteorological Centre, 1994. 1994 Climate Data, Nansha Station.

Nishemura, W., 1990. Incidental capture of sea turtles by Japanese research and training vessels: results of questionnaire. Marine Turtle Newsletter 51: 1-4.

UNEP (nd), Western Pacific. Regional Seas Directories and Biblographies: 329pp.

Wu, C-D., 1981. Report on the environmental and biological resources of Taipin Tao, South China Sea. I. Technical Report of Fishery Research Institute 33: 195-229.

Yang, Z-J., S-J. Hwang, S-S. Li, J-H. Tsi & L-J. Shun, 1975. Coral reef fishes and mollsucs. In: The Synoptic Investigation of Dungsha Tao. Institute of Oceanography, National Taiwan University, Taipei, R.O.C.: 1-5.