Status of sea turtles and their habitats in South central & Southern provinces of Vietnam Cuong The Chu
INTERNATIONAL UNION FOR CONSERVATION OF NATURE
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Status of sea turtles and their habitats in South central & Southern provinces of Vietnam
Cuong The Chu1
1 Institute of Marine Environment and Resources (IMER)
The designation of geographical entities in this book, and the presentation of the material, do not imply the expression of any opinion whatsoever on the part of The International Union for Conservation of Nature (IUCN) or the Institute of Marine Environment and Resources (IMER) or the U.S. Fish and Wildlife Services concerning the legal status of any country, territory, or area, or of its authorities, or concerning the delimitation of its frontiers or boundaries. The views expressed in this report belong only to the authors and shall not necessarily reflect those of IUCN, IMER, nor admit any commercial branding and procedure. This report has been made possible in part by the generous support of Marine Turtle Conservation Fund (MTCF), the U.S. Fish and Wildlife Services. Copyright: ©2019, International Union for Conservation of Nature and Natural Resources Reproduction of this report for educational or other non-commercial purposes is authorized without prior written permission from the copyright holder provided the source is fully acknowledged. Reproduction of this publication for resale or other commercial purposes is prohibited without prior written permission of the copyright holder. Citation: Chu, T.C. (2019). Report: Status of sea turtles and their habitats in south central & southern provinces of Viet Nam. Hanoi, Viet Nam: IUCN Viet Nam Country Office. 50pp. Front cover photo: A sea turtle in Con Dao National Park, Ba Ria – Vung Tau province, Viet Nam © Nguyen Hai Van/IUCN Viet Nam Back cover photo: A sea turtle heading back to the ocean in Con Dao National Park, Ba Ria - Vung Tau Province, Viet Nam © Le Phuong Tung/IUCN Viet Nam Layout by: Nguyen Thuy Anh & Nguyen Son Tra Available from: IUCN Viet Nam Country Office 1st Floor, 2A Building, Van Phuc Diplomatic Compound 298 Kim Ma Street, Ba Dinh District Hanoi city, Viet Nam Tel : ++(844) 37261575/6 (Ext: 131) www.iucn.org/vietnam
TABLE OF CONTENT
I. INTRODUCTION 4
1.1 Sea Turtle Conservation Status 4
1.2 Study Activities: 6
II. METHODOLOGY 7
2.1. Date and locations 7
2.2. Methodology 9
Interviews 9
Boat-based observations 9
Seagrass Beds 9
Coral reefs 10
III. RESULTS 11
3.1. Sea turtle nesting population 11
3.2. Sea turtle foraging populations 17
3.3. Status of coral reefs and seagrass beds 19
IV. THE THREATS TO SEA TURTLES AND THEIR HABITATS 31
4.1. Illegal catching 31
4.2. Habitat degradatin 32
4.3. The impacts related to economic activities 32
4.4. Increases in temperature due to climate change 33
4.5. Sea level rise 35
V. CONCLUSION AND RECOMMENDATION 37
VI. REFERENCES 39
I. INTRODUCTION
1.1 Sea Turtle Conservation Status Sea turtles are one of the oldest creatures on earth, appearing about 150 million years ago. Currently, there are 7 species of sea turtles within two families, Cheloniidae and Dermochelyidae. This includes the Green Turtle (Chelonia mydas and Chelonia mydas agassizii), Hawksbill Turtle (Eretmochelys imbricata), Olive Ridley Turtle (Lepidochelys olivacea), Kempi Turtle (Lepidochelys kempii), Loggerhead Turtle (Caretta caretta), Flatback Turtle (Natator depressus) and Leatherback Turtle (Dermochelys coriacea). Sea turtles are distributed across many tropical and subtropical regions, in warm waters, and in most oceans. Some species are even specific to one body of water. For example, the Flatback Turtle is found only in Eastern and Northeast Australia and the Kempi Turtle is found only in the Gulf of Mexico. For decades, sea turtle populations have been exploited for their meat and carapaces. Turtle meat is used in specialty food dishes while their carapaces are sold as decoration to tourists. Turtle populations are being decimated within their coastal habitats and on land. Coastal habitats are in danger due to uncontrolled fishing, unsafe fishing methods such as trawl nets, gill nets and long-line fishing, environmental pollution, degradation of seagrass beds, and the destruction of coral reefs. On land, the presence of humans on the offshore islands, the impact of light, waste, and noise pollution from boat engines, coastal erosion, and natural disasters such as floods and typhoons also contribute to the decline of sea turtle populations. However, calculating a precise number for the global sea turtle population is difficult due to measurement methods that are proved to be inaccurate. One such method is to count the number of females laying on beaches, but as males and juveniles do not frequent beaches, it is difficult to estimate their numbers in the wild. Compared to the populations of the 1930s, when sea turtles first began to be studied and documented, the number of Green turtles has decreased by at least 43% (Seminoff, 2004), Olive Ridley and Kempii turtles have been reduced by 50-60%, and Leatherbacks and Hawksbill turtles have decreased by nearly 80% (Mortimer & Donnelly, 2008; Spotila et al., 1996).
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The decline of all these sea turtle populations have resulted in their listing on the IUCN Redlist (List of endangered wildlife species) (Group, 1996). Vietnam is located in the western region of the East Sea/ Pacific Ocean with a total coastline of more than 3,450 km (includes the coastline inside and outside coastal areas, islands, and archipelagoes). With a total population of more than 97.5 million and land area of 310,060 km2 (315 people/km2), Vietnam is one of the most densely populated countries in the world with nearly 55% of the inhabitants concentrated in coastal areas (August 2019). The Exclusive Economic Zone (EEZ) covers an area of about 1 million km2 (UNLOS, 1982) and more than 3,200 islands, many among them remain unnamed (includes floating and submerged islands). Due to the location, geography, and climate of Vietnam's waters, it achieves a high level of biodiversity compared to other countries and regions around the world. Biodiversity at the level of diversity in species structure and composition, ecosystems, and genetics. Vietnam's waters are unique. Influenced by diurnal and semi-diurnal tides, its waters include more than 20 types of ecosystems that are renewable and highly productive, such as mangroves, coral reefs, seagrass beds, coastal tidal flats, coastal sandy beaches, lagoon systems. According to the Prime Minister's Decision No. 45/QĐ- TTg “Approval for the master plan of nation-wide biodiversity conservation by 2020, with a vision to 2030”, the total number conservation areas (both inland and sea) under the new law has increased to 219, of which there are 10 MPAs have been established including Cat Ba, Bach Long Vy, Con Co, Cu Lao Cham, Ly Son, Nha Trang Bay, Nui Chua, Hon Cau, Con Dao, Phu Quoc and 4 other MPAs have been planned: Hon Me, Hai Van - Son Cha, Phu Quy, Nam Yet. In Vietnam, five species of sea turtles have been recorded including the Green Turtle, Hawksbill Turtle, Olive Ridley, Loggerhead, and Leatherback. Research and studies on sea turtles in Vietnam still remain very limited. The first records of sea turtles distributed in Vietnam were published by Bouret R. (1941). According to this report, there are five species of sea turtles distributed throughout the coast of Vietnam and four species distributed in the Paracel Islands. From 1999 to 2008, international organizations and NGOs such as the International Union for Conservation of Nature (IUCN), the World Wide Fund for Nature (WWF), and the Trade Records Analysis of Flora and Fauna in
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Commerce (TRAFFIC) in collaboration with the Danish International Development Agency (DANIDA), the Ministry of Fisheries (now the Ministry of Agriculture and Rural Development), and Vietnamese research agencies, conducted research on the state of sea turtles. This research was conducted to protect sea turtles at spawning sites and develop a Sea Turtle Conservation Plan in Vietnam. The research conducted on sea turtles in Con Dao National Park (Ba Ria - Vung Tau), Nui Chua (Ninh Thuan) and other coastal locations across Vietnam showed that the populations of sea turtles and their nesting locations have been significantly reduced (Hamman et al., 2006). As a result of this research, all species of sea turtles in Vietnam have been included in the list of protected species by law (Decree No. 160/2013/ND-CP dated November 12, 2013): “Criteria to determine species and the regime of managing species under lists of endangered, precious and rare species prioritized protection”. However, the problem of illegal fishing and trading still exists. The number of Hawksbill and Leatherback sea turtles caught has increased significantly, but information on their feeding grounds and nesting beaches is limited. A survey conducted in the North and Central North provinces in 2017 by IUCN has confirmed the extinction of nesting Hawksbill and Leatherback in these areas. South Central and Southern Vietnam has very high levels of biodiversity and is incredibly rich in resources. These regions are home to unique and critical marine ecosystems such as seagrass beds, coral reefs, and mangroves. Previous studies have also shown that islands in these areas used to be nesting and foraging grounds of four diverse species of sea turtles (Green, Hawksbill, Olive Ridley, and Loggerhead sea turtles) (Con Dao, Hon Cau, Phu Quoc, Tho Chu…). Within the coastal habitats of Vietnam, both marine ecosystems and marine biodiversity are in constant decline. Even though many solutions for the management and protection of these regions have been applied, these protections and policies have not stopped the decline of native sea turtle populations. This study aims to provide the most accurate and up-to-date information on the status of breeding and feeding grounds of Hawksbill and Leatherback turtles and their habitats in this area, focused mainly on Con Dao archipelago and islands of Kien Luong lagoon (Nam Du, Ba Lua, Hai Tac, Phu Quoc).
1.2 Study Activities:
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Activity 1: Identify the nesting and foraging sites of Hawksbill turtle and Leatherback turtle in the South Central and South of Viet Nam, focusing on the islands in Ba Ria - Vung Tau and Kien Giang provinces with collected data from previous studies on sea turtle populations from Da Nang to Binh Thuan. Activity 2: Identify and assess the impacts of human activities and natural processes on sea turtles nesting and foraging habitats by investigating fishing, catching purposes, illegal trading, infrastructure building on nesting beaches, pollution discharge, transportation, etc.)
II. METHODOLOGY 2.1. Date and locations This study was conducted from February 2018 to June 2018 in five primary areas: Nam Du archipelago, Ba Lua archipelago, Hai Tac archipelago, Phu Quoc island (Kien Giang province), and Con Dao island (Ba Ria Vung Tau Province). Details of time and place of study are shown in Appendix (Table 2). In total, the study was conducted across 23 sites: 4 sites in Nam Du (Hon Mau, Do Nai, Dam Dam and Hon Dau), 5 sites in Ba Lua (Hon Heo, Ba Hon Dam, Hon Thach Hon, Hon Doi Moi, Hon Son Te), 3 sites in Hai Tac Islands (Tre Lon, Tre Tre, Hon Tre Vinh), 7 sites in Con Dao (Bay Canh, Hon Tre, Hon Cau, Ong Dung Bay, Northeast Bay and Mui Chim Chim, and 4 sites in Phu Quoc are Bai Bon, Bai Thom, Rach Vom and Rach Tram (Figure 1).
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Figure 1. Study sites in Kien Giang province
Figure 2. The study site in Con Dao island (Ba Ria – Vung Tau province)
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2.2. Methodology Interviews In order to obtain initial information of foraging populations in study sites, including locations, species, by-catch frequency, sizes, tags etc, each study site used two interview techniques: (1) Questionnaires and (2) lead questions. In the study areas, a total of 220 questionnaires were distributed and collected: 40 in Nam Du islands, 40 in Ba Lua islands, 40 in Hai Tac island, 40 in Phu Quoc islands and 60 in Con Dao islands. Boat-based observations Preliminary boat-based observations to assess the distribution and abundance of sea turtles were undertaken in 4 areas by local fishing boat (Phu Quoc, Nam Du, Ba Lua and Hai Tac islands). Boats navigated along the coastline in the middle of seagrass beds or coral reefs at a slow speed of 3km/h. The team of three researchers observed both sides of the boat to identify signs of breathing sea turtles. GPS coordinates were taken at the start and endpoints of each observation. Seagrass Beds The methods used to assess the status of seagrass beds were derived from the Survey Manual for Tropical Marine Resources (English et al. 1994). The line transect survey method was used in intertidal areas of the seagrass bed during low tide. The survey consisted of three people: one person handled the GPS and the other two observers collected nine samples along a transect. The observers drew a quadrat with 50cm x 50cm dimensions to observe and record: (i) overall seagrass percentage cover (ii) the species composition. Due to the size of the surveyed areas, two to three transect lines were analyzed in a direction parallel to the shoreline. In each study site, the leaves, roots and stems of seagrass were collected from 9 quadrats (50cm x 50 cm) to calculate the biomass (g/m2). All locations of collected samples have been recorded by GPS. On Phu Quoc island, the modified manta tow was applied to survey the distribution and living coverage of seagrass. In this method, the manta board was attached to the boat with a rope 17m in length. One observer gripped the board and towed
9 for approximately 2 to 5 minutes, then stopped to record the data. At the same time, a GoPro 5 camera was used to record the characteristics of the sea bottom. The videos recorded were then used to identify seagrass percentage cover and species composition. The end of the seagrass bed boundary was marked when there was 0 to <5 % seagrass cover, and then the boat would turn parallel to the shore and continue along a line adjusting its course depending on the boundary of the seagrass beds. The transect lines traveled by boat were continuously recorded by the GPS device. At the same time, the surveyor continually looked for sea turtles along the tracks.
Figure 3. Modified manta tow survey method
At each location, local people were interviewed. After receiving information on the sea turtle’s nesting beaches, foraging grounds, coral reefs and seagrass beds distribution, we visited these sites and conducted the surveys by following these methodologies in the respective order: boat-based observations, manta tow method, and quadrat method. Coral reefs Diving observations in a fixed transect (5 dives at 2 hour intervals) were conducted near the Nam Du islands. Surveys were carried out by two observers swimming along the 100 meters length transect. The pictures of 15 quadrats (50cm x 50cm) were randomly taken for the future analysis of the living coverage of corals and seagrasses. GPS coordinates were recorded at each site. Data analysis Using the GPS coordinates of the surveys, the spatial distribution of sea turtles was mapped, archived, and plotted on maps using colour coding. Google Earth software was used to display the distribution of sea turtle foraging grounds.
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III. RESULTS 3.1. Sea turtle nesting population According to previous studies, there are four species of sea turtles in Vietnam: Green turtles (Chelonia mydas), Hawksbill turtle (Eretmochelys imbricata), Olive ridley turtle (Lepidochelys olivacea) and Leatherback turtle (Dermochelys coriacea). According to the survey and monitoring program on sea turtles nesting along the Vietnamese coastline, 5 Green turtles frequently nest and Leatherback turtles occasionally nest. The Hawksbill and Olive ridley turtle species have not been observed laying eggs within the past ten years at any surveyed sites. Due to these observations, all species of sea turtles are included on the Red List of endangered wildlife species in Vietnam prioritized for protection according to Decree No. 160 / 2013 / ND-CP dated 12/11/2013.
Table 1. Sea turtle breeding species in Vietnam
Status in 2010 Status in 2019 (compared Species Vietnamese name (compared to 2000) to 2010)
Family Cheloniidae
Caretta caretta Quản đồng Declined Declined Increased in some protected Chelonia mydas Vích Declined 75% areas
Eretmochelys imbricata Đồi mồi Declined 90% Declined, no longer found
Lepidochelys olivacea Đồi mồi dứa Declined 90% Declined, no longer found
Family Dermochelyidae Declined, only found two Dermochelys coriacea Rùa da Declined 99% individuals for ten years
According to interviews, the central provinces of Quang Tri, Da Nang, Quang Nam, Quang Ngai and Binh Dinh were once extensive breeding grounds, with hundreds of females laying eggs every night within the nesting season. The numbers show a significant decrease of the female turtle populations. This seems especially true in areas with large populations, development, and tourism such as Son Tra Peninsula (Da Nang), Bai Dai (Cam Lam, Khanh Hoa), Tam Quan Bac (Phu Yen). Other locations still have a few individuals each year, the majority of which being green turtles (Quang Tri has about
11 ten individuals on 70 km of beach, Binh Dinh has about ten individuals in Hai Giang and Hon Kho beaches, 2-4 individuals in Khanh Hoa, and 3 - 5 individuals in Hon Cau, Binh Thuan). Other known breeding grounds have lost all of their sea turtles, such as in Bach Long Vy (Hai Phong), Phu Yen, Binh Dinh and Phu Quoc Island (Kien Giang) (Table 2).
Table 2. Number of sea turtles breeding in Vietnam Before 2001- 2011- STT Location Note 2002 2010 2018 1 Bai Tu Long (Quang Ninh) 15 10 1 2 Co To (Quang Ninh) - 3 3 3 Tran island (Quang Ninh) - - 2 10 1 4 Quang Tri 10 2* leatherback Kho inlet – Hai Giang (Binh 8 5 4 2 Dinh) - 1 6 Cam Lam (Khánh Hòa) 2 2* leatherback 7 Nui Chua (Ninh Thuan) 5 8 8 8 Hon Cau (Binh Thuan) - - 5 9 Con Dao (BR-VT) 217 282 523 10 Tho Chu (Kien Giang) - - 3 Total 255 319 551
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Figure 4. Distribution of sea turtle rockeries in Vietnam
(Red – Green turtle rockeries; Blue: Leatherback rockeries)
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According to estimates by Hamann (2006), the number of green turtles throughout Vietnam in the 1960s was approximately 1,000 per year. By 2002, the number of green turtles reduced to about 270, concentrated mainly in Con Dao, offshore islands in the Tonkin Gulf, central provinces from Da Nang to Ninh Thuan and 5 islands in the Gulf of Thailand (Hamann et al., 2006). By 2010, the number of female turtles nesting on the beaches of Con Dao was about 400 and continued to increase to more than 600 in 2018. Thus, the number of green turtles in Vietnam now has increased compared to the 2000s more than 50%. However, the number of nesting sites have decreased. Since the first observations in the 1960s, Green turtles have nested on the majority of the coastal beaches and islands on and near Vietnam. By 2002, the number of nesting sites decreased to 9 areas. At present, turtles are only nesting within 9 areas, 3 areas of which have been recorded recently (including Tran - Quang Ninh; Hon Cau - Binh Thuan; Tho Chu - Kien Giang) (Figure 3). The breeding season information on sea turtles in Vietnam has been wholly derived from the data of Green turtles in Con Dao. Green turtles often start to lay their nests at the beginning of the rainy season (late March), when the sand has been moistened and is durable enough to dig. Data shows that throughout the year, the number of Green turtles increases until a peak in July, which makes up over a quarter of the total number for the year and decreases gradually until the end of November. Nesting time’s highest concentration is from June to September, with an average of 83.12% of the total nests within the year.
Figure 5. The nesting season of sea turtles in Vietnam 14
3.1.1. Phu Quoc, Hai Tac, Ba Lua, Nam Su Islands in Kien Giang province (Figure 1) A recent survey shows that there are 4 species of sea turtles distributed in Phu Quoc, Nam Du, Ba Lua and Hai Tac islands (Kien Giang province). The Green Turtle (Chelonia mydas), Olive Ridley Turtle (Lepidochelys olivacea), Hawksbill Turtle (Eretmochelys impricata) and Leatherback Turtle (Dermochelys coriacea). Among them, the Green and Hawskbill are the two most abundant species. Based on interview data, before the 1990’s, nesting sea turtles could be found at any of the sandy beaches on the islands between April and December. The areas where nesting sea turtles used to be observe were: Bai Dai (Northern Phu Quoc, Ganh Dau community), Ba Hon Dung beach (Ganh Dau community), Mui Duong beach (Bai Thom community), Cay Da beach (Ham Ninh community), Ong Doi beach (An Thoi community) (Phu Quoc islands); in Hon Thit Mong, Hon Son Hai (Ba Lua islands); and in Hon Mau, Hon Ngang (Nam Du island). However, there is no evidence of nesting sea turtles on the beaches of all the study sites within Kien Giang province. Our surveys in Phu Quoc, Hai Tac, Ba Lua and Nam Du islands have shown no evidence of Hawksbill Turtle and Leatherback Turtle nesting within past nearly 40 years (since the 1980s).
3.1.2. Con Dao island, Ba ria – Vung Tau Province (Figure 2) In Con Dao area, sea turtles were surveyed nesting on the beaches at Tai island, Duong island, Cat Lon (Bay Canh island), Hon Cau MPA and Hon Tre Island. The results show that Cat Lon (Bay Canh Island) has the highest number of nesting turtles with an average of 671.7 ± 113 eggs/ nesting season (59%), followed by Hon Tre with 153 ± 23.4 eggs/nesting season (13%), Bai Duong 138.7 ± 26.6 (12%), Hon Cau 98.7 ± 37.2 (9%) and the lowest was Hon Tai 82.7 ± 41.3 (8%). All of the nesting turtles observed were Green turtles. Despite Ong Dung being previously home to the used the Hawksbill turtle according to interview data, no signs of these nesting turtles have been found. The interviews have also shown a recent increase in Green Turtle nesting in the Ong Dung area.
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Figure 6. Number of eggs and successful rate of Green turtle in Con Dao island (from 1990 to 2017)
Figure 7. Number of eggs in the significant nesting sites
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3.2. Sea turtle foraging populations So far, five species of sea turtles have been recorded live and forage along coastal areas and offshore islands. They include Green turtles (Chelonia mydas), Hawksbill turtles (Eretmochelys imbricata), Olive ridley turtles (Lepidochelys olivacea), Loggerhead turtle (Caretta caretta) and Leatherback turtles (Dermochelys coriacea). Although there is no quantitative research on the number of individual sea turtles currently feeding and living in Vietnamese waters, via interviews of fishermen who are fishing nearshore and offshore areas, it is possible that all five species are still active though their numbers have decreased significantly since 2002. Among the five species, Green turtles are the most abundant and distributed in all locations, followed by the Olive Ridley and Hawksbill turtles. Green turtles are usually found in shallow water areas with seagrass beds on offshore islands such as Phu Quy (Binh Thuan), Phu Quoc Island (Kien Giang), Con Dao (Ba Ria - Vung Tau), Hoang Sa (Da Nang), Truong Sa (Khanh Hoa), Bach Long Vi (Hai Phong). Moreover, the coastal waterbody is also home to the sea turtles, even inside the coastal lagoons such as Tam Giang - Cau Hai, Thuy Trieu. Other species (except Leatherback turtles) are often found in coral reefs and reefs in the Tonkin Gulf region from Quang Ninh to Thanh Hoa, the Central from Quang Tri to Binh Thuan, and the Gulf of Thailand (Dung et al. 2007). Leatherback turtles are rarely seen in shallow nearshore waters and are usually found only in inshore areas with insignificant numbers (with sightings being only every few years). Surveys conducted by the Research Institute of Fishery have shown that the sea turtle feeding areas often coincide with fishing grounds of gill nets, trawls, and tuna fishing lines. The interview data obtained from trawlers, gill nets, and hand lines fishers in 5 different localities (Quang Tri, Phu Yen, Binh Thuan, Ba Ria-Vung Tau and Kien Giang) showed that sea turtles were captured mainly in Central provinces, Con Dao area, Phu Quoc, Southwestern Hon Khoai (Ca Mau province) and the surrounding Truong Sa archipelago.
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Figure 8. The fishing grounds often bycatch sea turtles
(Do Van Thanh et al., 2019) In the nearshore water areas, surveys and interviews with local people in Kien Giang, Ba Ria, and Vung Tau provinces have shown that sea turtles (mainly Green turtle and Hawksbill turtle) are still foraging in the seagrass beds and coral reefs of Con Dao, Phu Quoc, Nam Du, Ba Lua and Hai Tac islands. Even though the sea turtle’s populations are very small, they are usually observed in the seagrass shadows at Bai Dai, Duong Cape, Bai Thom, Bai Bon, Ham Ninh (Phu Quoc); Hon Dau, Hon Mau, Hon
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Ngang (Nam Du island); Hon De, Hon Bo Dap (Ba Lua islands); and Hon Tre, Hon Tre Nho (Hai Tac islands). The edges of seagrass beds at Bai Bon, according to local fishermen, are where Green turtles usually feed and rest during the monsoon season, from September to January. Green turtles also appear and are caught in the area from Cay Sao cape to Da Bac cape, the northern part of Bai Vong (Ham Ninh) and rarely appear in Ong Doi cape (An Thoi). However, although we conducted 5 diving trips at Nam Du islands and 10 diving trips at Phu Quoc islands, no sea turtle has been seen. Manta tows above coral reefs and seagrass beds had similar results, neither foraging nor resting sea turtles could be found.
3.3. Status of coral reefs and seagrass beds Phu Quoc Seagrass bed Six species of seagrasses have been found in Phu Quoc island, including: Enhalus acoroides, Halodule uninervis, Halodule pinifolia, Cymodocea serrulata, Cymodocea rotundata, Thalassia hemprichii (Table 1). In comparison with previous studies, the number of species in Phu Quoc island has decreased from 10 species (2006) to 6 species, 4 species are absent: Syingdium isoetifolium, Halophila ovalis, Halophila minor and Halophila decipiens (Tiến 2008). The dominant species across all seagrass beds were Enhalus acoroides, Thalassia hemprichii, Cymodocea serrulata and Halodule uninervis. Enhalus acoroides (35%) and Thalassia hemprichii (25%) were the most abundant in the seagrass survey. The third most abundant species was Cymodocea serrulata at 20% abundance. Halodule uninervis and Halodule pinifolia were only 5%.
Figure 9. Seagrass species composition in Phu Quoc island 19
Seagrass beds are distributed along the North Eastern, Eastern, and South-Eastern regions of the island in the shallow water areas (maximum 6 meters depth). Among the study sites, Bai Bon is the richest location being home to 6 species of seagrass. Bai Thom and Rach Vem have only 4 species (Table 3). In Bai Bon, where the intertidal zone was mostly silt, the dominant species were Enhalus acoroides, Thalassia hemprichii, Cymodocea serrulata and Halodule uninervis. Other sites in Bai Thom and Rach Vem where the intertidal zone was mostly sandy, the dominant species were Thalassia hemprichii, Cymodocea serrulata.
Table 3. Species composition and distribution of seagrass in Phu Quoc island
No Species Distribution Rach Vem Bai Thom Bai Bon Ham Ninh Hydrocharitaceae 1 Enhalus acoroides + ++++ 2 Thalassia hemprichii +++ + ++ +++ Cymodoceaceae 3 Halodule pinifolia + + 4 H. uninervis + + + + 5 Cymodoceae rotundata ++ ++ ++ 6 C. serulata ++ +++ ++ Total 4 4 6 4
Figure 10. Distribution of seagrass bed in Phu Quoc island 20
In June 2018, surveys on area and living coverage of seagrass beds showed the main concentrations to be in Bai Bon, Bai Thom, Rach Vem and Rach Tram. The results show that the total area of seagrass beds was 4,648 ha. At Bai Bon, seagrass beds are distributed over a total area of about 2,500 hectares. Seagrass beds are located 4.5 km from the shore, at a depth of about 2.5 - 12 meters. Before 2013, the Rach Vem seagrass area showed 900ha but has since decreased to only 600 ha (2016); about 25% of the area. With a total area distribution of over 10,000 hectares, Phu Quoc is recognized as the largest seagrass area in Vietnam. According to Cao Van Luong (2016), the seagrass area measured 6,560 ha. A survey of the same area conducted in 2004 measured 10,270 ha (Nguyen Van Tien, 2002, 2006, 2013). The results show a net loss of 36% over 12 years. The largest seagrass meadows in Phu Quoc is Hon Dam and Bai Khem areas, with a total area of 4,000 ha of grass, a decrease of 1,300 ha compared to 2004 (The average coverage of seagrass in Phu Quoc is quite high (55.8%) higher than in 2004 (43.38%) (Nguyen Van Tien, 2002, 2006, 2013). However, coverage fluctuates within different study sites. The average coverage of seagrass varies from 37.5% (Ham Ninh), 60.0% (Hon Dam, Bai Khem, Ganh Dau and Rach Vem), 87.5% (Ong Doi yards).
Table 4. The fluctuation of seagrass beds in Phu Quoc Area of distribution (ha) Living Locations Before Dec 2016 Apr 2018 coverage (%) 2013* (Rainy season) (Dry season) Ham Ninh, Ganh Dau, Da 600 300 1,700 25 - 75 Bac Bai Bon 2,000 1,200 2,500 25 - 100 Rach Vem 900 600 448 50 - 75 Hon Dap - Bai 6,300 4,000 - 60 Khem Ong Doi 470 410 - 87.5 Total 10,270 6,510 - * Nguyen Van Tien (2002, 2006, 2013)
The living coverage percentage of seagrass beds in Phu Quoc ranges from 40% to 70%. Bai Bon is highest where living coverage percentages are up to 70% (Table 4). Due to the high density of large Enhalus acoroides (average height is 88 cm), the biomass of seagrass at Bai Bon is highest, up to 6261 (g /m2). Rach Vem is home to the smallest 21 amounts of biomass (only 2625 g/m2), the most abundant species here is Thalassia hemprichii (average height is 9.4 cm). The biomass of Bai Thom ranges from 178 to 451 (g.dry/m2). Table 5. Biomass of seagrass in Phu Quoc island
No Locations EA TH CS CR HU HP 300,96 ± 261,36 ± 281,1 ± 377,15 ± 1 Rach Vem 61,91 47,71 24,08 84,49 451,21 ± 2 Bai Thom 178,67 ±4,3 48,86 219,81 ± 269,54 ± 320,35 ± 136,08 ± 103,67 ± 3 Bai Bon 38,11 32,6 29,1 9,49 8,31 EA – Enhalus acoroides, TH – Thalassia hemprichii, CS – Cymodocea serrulata, CR – Cymodocea rotundata, HU – Halodule uninervis, HP – Halophila pinifolia Bai Bon is the largest seagrass meadow near Phu Quoc island with a total area of 2200 ha. The second largest being Rach Vem (950 ha). Bai Thom is lowest with only 179 ha. In 2017, the total area measured 3,619 ha (Ham Ninh excluded); 2.3 times higher than in previous years. Along the manta tow contours, the area at Bai Thom 1 is very poor, small seagrass areas are scattered with living coverage percentage less than 25% and 80% of the bottom is sandy mud and corals are sparse.
Figure 11. Enhalus acoroides and Thalassia hemprichii in Rach Vem
Phu Quoc Coral Reef Coral reefs in Phu Quoc are mainly distributed in the Northern part of the island (in the An Thoi archipelago). Based on surveys conducted by IMER, Phu Quoc has recorded 86 species of hard coral (33 genuses) and 8 species of soft corals. The coral reefs are also in good condition compared with a previous study by the WWF in 1994. A
22 total of 25% coral reefs of are recorded to be in good condition, 58.3% in average condition, and 16.7% of coral reefs in poor condition. The most common genus are Acropora, Porites, Pavona, and Montipora. According to the survey, the quality of coral reefs in Phu Quoc is high. This includes the reefs in the Hon Xuong and Hon Thom with coverage being 62.5 and 51.25% qualifies a level 4 reef (good reefs). This is followed by the Mong Tay island and Roi Islet having 46.8% and 41.15% coverage, qualifying level 3 (pretty reefs). There are no signs of new dead corals or impacts affecting the reefs.
Figure 12. Distribution of coral reefs in Phu Quoc
Ba Lua islands There are two sites where seagrass beds are distributed near Ba Lua island. Ba Hon Dam is larger (34 ha) and Hon Heo is smaller (4.5 ha). Five seagrass species are found in Ba Lua area: Enhalus acoroides, Thalassia hemprichii, Halodule pinifolia, Cymodocea rotundata and Halodule uninervis). The dominant species in Ba Hon Dam were Enhalus acoroides and Thalassia hemprichii, and in Hon Heo were Thalassia hemprichii, Cymodocea rotundata and Halodule uninervis.
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Figure 13. Halodule uninervis and Thalassia hemprichii in Hon Heo
Figure 14. Distribution of seagrass in Ba Lua islands
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Figure 15. Enhalus acoroides meadow in Ba Hon Dam
Hai Tac islands
In Hai Tac islands the sediment is primarily sand and fine sand and the depth is around 1 – 3m with an average of 1.8m. The most diverse and dense area of seagrass species is Hon Tre Nho, where there were 5 species: Thalassia hemprichii, Enhalus acoroides, Cymodocea serrulata, Cymodocea rotundata and Halodule uninervis. The most abundant species in this area is Cymodocea serrulata, followed by Thalassia hemprichii. Halodule uninervis was only found in shallow water in Hon Tre Nho. The area of seagrass beds near Hai Tac island is very small (about 16 ha total). Hon Tre Lon has a total of 9 ha, Hon Tre Nho has 5 ha and Hon Tre Vinh has 2 ha. However, the living percentage within beds is higher than that of Phu Quoc island. Hon Tre Nho is the highest site in terms of living coverage (up to 80%); this is followed by Hon Tre Vinh (60%), and Hon Tre Lon (50%).
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Cymodocea serrulate Thalassia hemprichii
Enhalus acoroides Halodule uninervis
Figure 16. Species of seagrass in Hai Tac island
Figure 17. Distribution of seagrass beds in Hai Tac
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Con Dao islands Con Son bay (8°40'38.74"N; 106°36'50.26" E) has a high seagrass distribution. The dominant seagrass species is Halophila ovalis, with a living coverage of more than 80%. Halophila ovalis is a critical seagrass species in the diet of sea turtles, dugongs, and other various species. During the field survey, traces of sea turtles were recorded including: grazing in the deep sand and signs of breathing on the water’s surface. However, the age and sex of the sea turtles could not be determined. Presently, with the development of tourism in Con Dao, 50-100 high-speed boats are recorded daily traveling around the tourism dock. These activities threaten the foraging sea turtle population and significantly affect the breeding turtle populations in the area.
Figure 18. Halophila ovalis in Con Son area and the grazed track of sea turtles
Beside Halophila ovalis, two other species Syringodium isoetifolium and Halodule pinifolia have been found in the nearshore area.
Figure 19. Syringodium isoetifolium and Halodule pinifolia
The corals in Con Son Bay are distributed into small groups on a hard bottom outside of the seagrass beds. Some branch coral colonies are scattered amongst the bottoms of dead corals. Massive corals are also scattered across the bottom of the coral
27 reef. The hard corals are showing signs of recovery, however, since recovery for corals is slow, fast growing seaweeds compete for light and can cause coral damage.
Figure 20. Branch and massive coral colonies found in Con Son bay
Hon Bay Canh (point 1; 8 ° 39'58.10 "N; 106 ° 40'57.91" E) located to the South of Bay Canh, is an area with sandy beaches where turtles in the area regularly nest during the breeding season. This is one of the strictly protected areas, under the supervision of Con Dao National Park. However, even with these protections, the ecosystems in the tidal zone are showing poor conditions. Only dead corals were found with no signs of coral recovery in the survey area.
Figure 21. Dead corals in the Southern side of Bay Canh
Hon Bay Canh (point 2; 8°40'28.45 "N; 106°40'52.99" E) is in the North of Hon Bay. In contrast to the south side of Hon Bay, the northern part of the coral reefs are highly developed. Throughout the survey, many sights were reported with a high coverage of reef (80%). The coral group grows into large reefs. The northern reef section is one of the most famous coral tourist destinations, as noted by the management unit of Con Dao National Park. Tourist activity, such as swimming and snorkeling, in the area has a significant impact on the conservation of the coral reef ecosystems. Climbing on or
28 simply touching corals can cause them to break or lose sedimentation. A loss for coral reefs can have a deepening impact on the surrounding corals and wildlife.
Figure 22. The large coral colonies in the northern side of Bai Canh
Bai Lo Voi (8°41'22.21"N; 106°37'44.32"E) has seagrass beds with two dominant species distributed at a depth of 15m: Halodule pinifolia and Halophila ovalis. Although the survey site has a sandy bottom and high turbidity, the living coverage of seagrass is over 40%. Sea Turtle grazing tracks were recorded on the bottom, but with less frequent than that of Con Son bay.
Figure 23. Distribution of Halodule pinifolia and Halophila ovalis in 15m depth
Hon Cau (8°41'11.23 "N; 106°44'12.18" E) has a soft bottom with coral reefs stretching up to 1 km in length and 250m in width. The coral in this area is well developed, considered one of the most beautiful coral reefs in Vietnam, with a density of over 90%. The species diversity of coral is very high, especially among branch coral species (Vo Si Tuan, 2010).
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Figure 24. Coral reefs in Hon Cau island In Mui Chim Chim (8°41'32.53 "N; 106°38'59.35" E) the coral reef area is located in shallow water, stretching for nearly 2 km to the Six Senses Con Dao Resort. The coral reefs in this area are well developed with a high diversity of species composition. The width of the reef is about 100 - 250 m from the shoreline, coral reef here is one of the most beautiful reefs in Con Dao. Mui Chim Chim has the highest living coverage rate (> 80%). Tourist activity for this region is also considerably high and observable.
Figure 25. Coral colonies in Mui Chim Chim
Ong Dung Bay (8°42'32.87 "N; 106°35'10.90" E) is located west of Con Dao. This bay has a small distribution of seagrass. Since the time of the survey was seaweed season, the coral colonies on the hard bottom (rocks, dead corals) were covered by seaweeds.
Figure 26. Seagrass and corals in Ong Dung bay
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Figure 27. Distribution of coral reefs in Con Dao archipelago
IV. THE THREATS TO SEA TURTLES AND THEIR HABITATS 4.1. Illegal catching Recent studies show that sea turtle populations and their habitats in Kien Giang are threatened by fishing activities. The local fishermen of Bai Thom and Ham Ninh previously used the drill net method for large game fishing (rays, sharks). However, these methods also caught sea turtles and dugongs. In recent years, due to the awareness raising programs and fishery legislation by the Government in Kien Giang and Ba Ria – Vung Tau provinces, the drill net method has been almost entirely stopped. However, other illegal methods such as bottom trawling and diving with electricity equipment are still being used in shallow water areas, coral reefs, and seagrass beds. As a result, a large number of incidental catching of dugongs and sea turtles have been reported. If caught, either by accident or on purpose, almost all dugongs and sea turtles are slaughtered and illegally consumed in fishery villages along Phu Quoc or transported to Ha Tien to be sold.
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Figure 28. Green and Hawksbill turtles in Ha Tien fish market (4/2018)
4.2. Habitat degradatin The primary food source of dugongs and sea turtles are seagrasses and corals. Therefore, they are usually distributed around seagrass beds and coral reef areas. Recent studies have shown that seagrass beds and coral reefs in Phu Quoc, Ba Lua, and Hai Tac islands are in a process of degradation. The major contributor to the decline of dugong and sea turtle ecosystems is human activity. This is mostly due to overexploitation of natural resources and infrastructure development (transportation, buildings, ports, construction). In some locations such as Bai Bon, the living coverage of the species Halophila ovalis a favorite food of dugong, has completely disappeared due to the bottom trawl fishing activities.
4.3. The impacts related to economic activities The Seagrass beds distributed near the communities of Ganh Dau, Bai Thom, and Ham Ninh, are where sea turtles and dugongs are frequently observed and caught. The total number of fishing vessels of these three communities exceeds 900 (2012). This count contains mainly small boats that operate in the shallow areas near seagrass distributions. Notably, there are many bottom trawl boats and double-trawl boats within the larger body of water near Kien Giang. Even though these fishing methods have been suspended, they still illegally operate in shallow water areas near Phu Quoc island. The intensity of human fishing activities is a large threat to the life of sea turtles and dugongs. According to interviews conducted by the Research Institute of Marine Fishery (2018) of hand line vessels in 5 localities (Quang Tri, Phu Yen, Binh Thuan, Ba Ria-Vung Tau, and
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Kien Giang), the proportion of accidental catches of sea turtles in hand lines is 86.0%, The rate is 39.3% in trawl and 31.0% for gillnet fisheries. A total of 261 sea turtles were accidentally captured by fishing methods in 2018, of which, hand line fishing caught 85 individuals (average 1.7 individuals/vessel), trawler fishing caught 84 individuals (average 0.56 individuals/vessel) and gillnet fishing caught 92 individuals (average 0.46 individuals/vessel). The proportion of vessels accidentally catching sea turtles is relatively high: trawler fishing (54.2%), gill net fishing (45.2%) and hand line fishing (18.6%). The number of fishing vessels recorded in Vietnam is 109,622 as of 10/2017. Of which, 36,518 are gillnet vessels, 19,574 are trawler vessels, and 18,462 are hand-line vessels. As many as 27,791 individual sea turtle have been captured accidentally -- much higher than previous estimations of 1000 individuals/year.
4.4. Increases in temperature due to climate change Climate change (including global warming, rising sea levels, and extreme weather events) poses a significant threat to ecosystems and wildlife around the world (Fuentes, Fish, & Maynard, 2012). The impacts of climate change have been recorded throughout many ecosystems, plant and animal species, and ecological processes (Walther et al., 2002). In order to have an effective management plan for ecosystems and wildlife species, climate scenarios of the future need to be calculated.
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Figure 29. The fishing grounds of some typical fishery methods (sources..)
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At present, the sand temperature in Bai Meat (Nui Chua) at its highest is 30.8oC and lowest at 27.8oC in Bay Canh (Con Dao); other beaches in Con Dao have a similar sand temperature of 28.3oC. According to climate change predictions, by 2030, the sand beach temperature in Con Dao will increase from 0.67-0.93oC. with Bay Canh beach having the highest increase of 0.93oC. Bai Meat at Nui Chua will expect a lower increase, from 0.54 to 0.69oC. By 2050, the increase in Con Dao is predicted to be 1.16-1.57oC, equivalent to the increase in Nui Chua. The temperatures of beaches currently already exceed the gender balance heat for sea turtles. By 2010, temperature increases across all beaches were high, ranging from 1.14 to 3.12oC, of which the beach at Bay Canh island had the highest temperature increase. Since sea turtles are sex dependent based on environmental conditions, high incubation temperatures produce more females. Based on the sand beach temperature under climate change predictions, the current rate of female hatchlings in Nui Chua is up to 82.6%, much higher than Con Dao (the average female rate is 38.2 ± 4.73%). Even in Con Dao, the percentage of females born on the beaches is different due to different incubation temperatures, of which Bay Canh beach has the lowest percentage of female hatchlings (26%) with other beaches having a percentage of females ranging from 40% to 44%. By 2030, the percentage of female hatchlings in Nui Chua (Ninh Thuan) will increase to 93-96%, while in Con Dao this rate will be 64-67%. By 2050, most of the baby turtles at Nui Chua will be female and in Con Dao will be between 79 and 86%. By 2100, all offspring born at Nui Chua and Con Dao will be female, except for the low emission scenario B1 in Con Dao (89%). (Cuong et al., 2013).
4.5. Sea level rise In the scenario of sea-level rise, factors such as elevation, width, and slope of a beach are the most critical determinants of flooding. In all three climate change predictions (B1, B2 and A1FI), the three breeding sites with the highest number of egg nests, Cat Lon (59% of the whole nesting area), Duong Duong and Hon Tre (25% of the whole nesting area) are the most at risk. By 2100, these beaches are likely to be flooded by up to 85% in all climate change scenarios. These beaches have a small area and width and only 4-10% of the total area is used by sea turtles to lay eggs. This is considerably lower than the other beaches (Hon Tai 38% and Hon Cau 13%, Nui Chua 60%). Bai Meat 35 in Nui Chua is the largest area suitable for sea turtles to lay eggs, but the number of nests here is minimal (average 8 nests/season), so the area is likely to be the lowest affected. Sea turtles nesting from June to August (the peak breeding period) will be most affected by sea-level rise combined with high tides from August to October. The estimated average area predicted to be lost from 2020 to 2100 under climate change scenarios is B1 = 6-29%, B2 = 7-34%, and A1FI = 7-45%. By 2100, the number of nests lost due to flooding will be 37% (B1), 43% (B2) and 59% (A1FI) of the total number of nests in the whole season (Cuong et al., 2013).
4.6. Marine Pollution Pollution can have serious impacts on both sea turtles and the food they eat. For example, new research suggests that a disease now killing many sea turtles (fibropapillomas) may be linked to pollution in the oceans and in nearshore waters (Santos RG et al., 2010). When pollution contaminates and kills aquatic life, it also destroys feeding habitats for sea turtles. Oil spills and urban runoffs of chemicals and fertilizers all contribute to water pollution. An estimated 36% of all marine pollution from oil comes through drains and rivers from cities (Transportation Research Board and National Research Council, 2003). Fertilizers also make up a large proportion of marine pollutants. Runoff from farms and lawns cause eutrophication within plants from the consumption extra nutrients. Eutrophication is an explosion of algae blooms that can deplete the water’s oxygen and suffocate marine life. Eutrophication has created enormous dead zones in many parts of the world, including the Gulf of Mexico. Improper sewage disposal is another factor that causes eutrophication. A University of Exeter study from 2017 showed that hundreds of sea turtles die every year after they become entangled in plastic. Last year, Exeter scientists detected microplastics in the guts of nearly 100% of sea turtle species in the Atlantic and Pacific Oceans and the Mediterranean Sea, as microplastics absorb heat, their presence may raise the nest incubation temperature, skewing the sex ratio towards females. Since plastic bags look very similar to jellyfish and fishing nets often look like seaweed, sea turtles often mistake floating plastic garbage for food. They can choke,
36 sustain internal injury, drown, or starve to death due to plastic consumption. Plastic also creates pockets of air in their gut, making diving difficult. In recent years, global turtle population numbers have noticeably decreased due to plastic consumption. Research conducted by the Commonwealth Scientific and Industrial Research Organization (CSIRO) and the University of the Sunshine Coast (USC) found that a turtle had a 22% chance of dying if it ate just one piece of plastic. Once a turtle has ingested 14 plastic items, the mortality rate increased to 50%. An estimated 8 million metric tons of plastic enters the oceans every year. This poses one of the greatest threats to the health of global marine ecosystems. A great deal of research is currently underway, but effectively addressing ocean plastic pollution requires a multidisciplinary and collaborative approach with engagement from a wide range of sectors and actors. Vietnam is one of the top four countries contributing to the pollution of the ocean with plastic waste and debris (Jambeck et al., 2015) due to its mismanagement.
V. CONCLUSION AND RECOMMENDATION - Our surveys have shown that the Hawksbill and Leatherback turtles have disappeared from the beaches in the South and Central South provinces for at least 30 years, according to interviews. The only species recently found to be nesting is the Green turtle on Con Dao island. - Green turtles are frequently observed in studied sites, while Hawksbill turtles, Olive Ridley turtles and Loggerhead turtles are less common. We did not find any evidence of Leatherback turtles foraging in these areas. - The number of foraging populations has also declined. Most sea turtle samples found are from foreign water bodies; mostly Cambodia and Thailand. - Sea Turtle habitats: seagrass beds and coral reefs in study sites are also degraded even in the Marine Protected Areas. These trends could worsen in the future due to the economic development and high population of these small islands. - The decline in the population of sea turtles in Vietnam is related to the overuse of nesting beaches, illegal fishing practices, illegal trading of sea turtles and their products, loss of nesting and foraging habitats, and environmental degradation.
Recommendations 37
1. Sea turtles and marine mammals share habitats and threats, as all the species studied are either considered endangered and/or nearly extinct. As a flagship species, sea turtles and their ecosystems are indicators that reflect a healthy environment, and help create public awareness and attract the participation of communities. Moreover, as an immigrating species, sea turtles are not bound by international borders. Therefore, cross-border cooperation between Vietnam and its neighboring countries, Cambodia, Thailand, Philippine, Malaysia etc., is the most urgent and highest priority. 2. Designing and implementing an awareness education program to increase the awareness of local people and tourists about the conservation of rare species like dugongs and sea turtles. The awareness raising program should primarily focus on youth and students from primary schools to high schools. 3. The seagrass beds in Ba Lua and Hai Tac islands need to be protected. Because the area is small, community-based conservation sites may be the best solution. Local fishermen who fish/farm in the areas should be involved in and benefit from seagrass protected areas. 4. Sea turtles have existed for hundreds of millions of years and are highly adaptable to environmental change. However, it is difficult for sea turtles to adapt to the current rapid changes of the environment due to climate change without management and protection measures. The fourth objective is to reduce the incubation temperature in Con Dao and Nui Chua incubation sites to the same temperature as the natural beach by covering from direct sunlight. 5. Measures to reduce sea turtle mortality, by intentional or unintentional exploitations, by strengthening the management of breeding and foraging grounds need to be implemented. 6. Build a database for sea turtles in order to study their biological and ecological characteristics and assess the ecological risks due to fishing activities. 7. Rescue centers for sea turtles and marine mammals should be established with the MPA network along the coasts of Vietnam.
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VI. REFERENCES
Agriculture, F. a. C. D. (2006). Conservation of sea turtles in Hong Kong. Retrieved from http://www.afcd.gov.hk/english/conservation/con_fau/con_fau_sea/con_fau_sea_con/con _fau_sea_con_sat.html Al-Merghani, M., Miller, J. D., Pilcher, N. J., & Al-Mansi, A. (2000). The green and hawksbill turtles in the Kingdom of Saudi Arabia: Synopsis of nesting studies 1986-1997. Fauna of Arabia, 18, 369-384. Bộ, Đ., & Minh, N. H. (2013). Ước tính trữ lượng và dự báo sản lượng khai thác nguồn lợi cá ngừ đại dương năm 2013-2014 ở vùng biển xa bờ miền Trung. Tạp chí Khoa học ĐHQGHN, Các Khoa học Trái đất và Môi trường, 29(2), 11-16. Booth, D. T. (2006). Influence of incubation temperature on hatchling phenotype in Chan, E.-H. (2013). A report on the first 16 years of a long-term marine turtle conservation project in Malaysia. Asian Journal of Conservation Biology, 2(2), 129-135. Charuchinda, M., Sakamoto, W., Arai, N., & Monanansup, S. (2002). Migration pattern of post-nesting green turtle in the Gulf of Thailand Paper presented at the Proceedings of the 3rd Workshop on SEASTAR2000, Thailand. Cuong, C. T. (2009). Status of marine turtles at Bai Tu Long bay and Co To island (Quang Ninh province). The Institute of Marine Environment and Resources. Unplublished report to IUCN Viet Nam. Cuong, C. T. (2010). Status of marine turtles in Quang Tri province. The Institute of Marine Environment and Resources. Unpublished report to IUCN Viet Nam. Cường, C. T. (2011). Hiện trạng rùa biển tại Trường Sa và các đe dọa. Paper presented at the Kỷ yếu hội thảo quốc gia về Khoa học và Công nghệ biển, Hà Nội, Việt Nam. Giang, N. T. (2010). Study some biological characteristics of Green turtle (Chelonia mydas) in Con Dao islands. (Master). The University of Agriculture and Forestry in Ho Chi Minh Ho Chi Minh. Group, M. T. S. (1996). Lepidochelys kempii. IUCN Red List of Threatened Species. Gyuris, E. (1994). The rate of predation by fishes on hatchlings of the green turtle (Chelonia mydas). Coral Reefs, 13(3), 137-144. Retrieved from
Hirth, H. F. (1980). Chelonia mydas (Linnaeus). Green turtle. Catalogue of American Amphibians and Reptiles, 1-4. Retrieved from
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Trono, R. B. (1991). Philippine marine turtle conservation program. Marine Turtle Newsletter, 5-7. Retrieved from
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Appendix: Table 1. Characteristics of some important nesting beaches Attitude Slope Type of Colour Vegetable Area in Area in Area of Lengt to (cm/ m) sediment coverage Beach low tide high tide nesting h (m) 0mHĐ (%) (ha) (ha) (ha) (m) Small size dark yellow 90 649 31.37 1.365 0.137 4.6 ± 0.4 11.5 Cat Lon grain Bai Duong 354 45.29 0.739 0.060 4.3 ± 0.4 16.4 Big grain dark yellow 10 Hon Tre 196 1.61 0.335 0.015 5.4 ± 0.4 9.5 Big grain dark yellow 40 Middle size dark yellow 50 544 6.15 1.768 0.233 4.2 ± 0.3 4.2 Hon Cau grain Hon Tai 119 0.34 0.149 0.057 6.4 ± 0.9 33.6 Big size grain dark yellow 10 Nui Chua 785 43.16 1.793 1.037 5.1 ± 0.7 4.1 Big size grain dark yellow 5
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1. Cat Lon beach (Con Dao)
2. Bai Duong (Con Dao)
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3. Hon Tre (Con Dao)
4. Hon Cau (Con Dao)
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5. Hon Tai (Con Dao)
6. Nui Chua (Ninh Thuan)
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Table 2. Study time and locations
Time Locations Method used
Nam Du islands Nam Du, An Son, Hon Mau, Hon Do - Interviews Nai, Hon Bo Dap, Hon Dau 21-23/03/2018 - Boat survey
- Diving survey
Ba Lua islands - Interviews Son Hai, Hon Heo, Ba Hon Dam, Hon 26-28/03/2018 - Boat survey Thach Mong, Hon Doi Moi, Hon Son Te - Diving survey Hai Tac islands - Interviews Tien Hai, Hon Tre Lon, Hon Tre Nho, 31/03-01/04/2018 - Boat survey Hon Tre Vinh - Diving survey Con Dao island - Interviews Ong Dung, Hon Bay Canh, Hon Tre 10-13/05/2018 - Boat survey Lon, Hon Cau - Diving survey Phu Quoc archipelago - Interviews Duong Dong, An Thoi, Bai Thom, Rach - Boat survey 13-16/06/2018 Vem, Rach Tram, Bai Bon. - Diving survey - Manta tow
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